Difference between revisions of "Hamsters (Laboratory) - Pathology"

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==Introduction==
 
==Introduction==
 +
Hamsters are now commonly used in laboratory testing, but for many years other species including mice, rats and guinea pigs were used for studies requiring small easily managed animals. In 1919 the first study using hamsters was undertaken assessing the susceptibility of Chinese hamsters to ''leishmania''. A number of difficulties were encountered including an inability to breed the animals and hamsters were not used again until the 1930s when a Syrian hamster burrow was uncovered by an archaeologist near Aleppo. Nearly all common golden hamster breeds are related to these wild discovered hamsters. Syrian hamsters ''(Mesocricetus auratus)''were used and were found to be easier to breed and had more desirable traits for laboratory testing than Chinese hamsters. Syrian hamsters have gone on to become the most commonly encountered laboratory hamster species with around 500,000 per year currently used in the US. However, approximately ten times more mice and rats are used compared to hamsters.
  
 
==Strains and Stocks==
 
==Strains and Stocks==
 +
Although Syrian hamsters ''Mesocricetus auratus'' or Golden hamsters are the most commonly encountered laboratory species, a number of other species are also used. These include the Chinese hamster ''Cricetus cricetus'', the Armenian hamster ''Cricetulus migratorius'', the Dzungarian hamster ''Phodopus sungarus'' and the South African hamster ''Mystromyx albicauafus''. There are a number of [[Hamster_Breeds_-_WikiNormals|differences between these types of hamster]];
 +
{| class="wikitable" border="1"
 +
|-
 +
! Breed
 +
! Description
 +
|-
 +
| Syrian/Golden
 +
| Compact body, short legs, 4 front toes, 5 rear toes, 120g, approximately 15cm long, short tail, dark ears, females larger than males.
 +
|-
 +
| Chinese
 +
| usually grey with a black stripe down its back, 30-35g.
 +
|-
 +
| European
 +
| usually has a black bely
 +
|-
 +
| Dzungarian
 +
| varieties include siberian, dwarf, striped and hairyfooted. 30-35g. Summer coat is brown and winter is white.
 +
|-
 +
| South African
 +
| usually white tailed.
 +
|-
 +
|}
  
 +
==Physiology==
 +
Please find details of hamster physiology within the WikiNormals section.  Physiological information available includes “[[Hamster_Physiology_-_WikiNormals|General]]”, “[[Hamster_Biochemistry|Biochemical]]”, “[[Hamster_Haematology|Haematological]]” and “[[Hamster_Breeds_-_WikiNormals|Breed]]” parameters.
 +
<br />
  
−
==Physiology==
+
==General Behavioural Characteristics==
−
Please find details of hamster physiology within the WikiNormals section. Physiological information available includes “[[Guinea_Pig_Physiology_-_WikiNormals|General]]”, “[[Guinea_Pig_Biochemistry|Biochemical]]”, “[[Guinea_Pig_Haematology|Haematological]]” and “[[Guinea_Pig_Breeds_-_WikiNormals|Breed]]” parameters.
+
In particular, Syrian hamsters are solitary and only tolerate company when breeding. Females are easily disturbed and aggressive when lactating or pregnant and in such situations, can be prone to kill other hamsters. Cannibalism is common in stressed primiperous females. Chinese hamsters are particularly pugilistic.
−
<br>
+
<br />
−
<br>
 
 
==Anatomy and Histology==
 
==Anatomy and Histology==
 
This section has been included to allow familiarisation with the peculiarities of hamster anatomy to provide a context for some of the disease and pathological headings found below. Therefore only anatomical areas with specific features warranting emphasis have been included below;
 
This section has been included to allow familiarisation with the peculiarities of hamster anatomy to provide a context for some of the disease and pathological headings found below. Therefore only anatomical areas with specific features warranting emphasis have been included below;
 +
===Integumentary System===
 +
'''Hip/Flank Glands'''
 +
<br />
 +
Sebaceous glands with pigmented cells and terminal hairs that secrete during sexual arounsal in both sexes. Also used for olfactory territorial marking.
 +
<br />
 
===Reproductive System===
 
===Reproductive System===
 +
'''Vaginal Discharge'''
 +
<br />
 +
Post-ovulatory dimethyl disulphide is used as a breeding tool by females but is often mistaken for an inflammatory exudate due to its similarity in smell to rotten eggs.
 +
<br />
 +
<br />
 +
'''Sexual Dimorphism'''
 +
<br />
 +
Male Syrian hamsters have much larger adrenal glands than females despite females being generally larger than males.
 +
<br />
 +
<br />
 +
'''Fostering Newborn'''
 +
<br />
 +
This is not usually possible in hamsters as infants are extremely immature when born and 'foreign' infants usually do not accept one another.
 +
<br />
 +
<br />
  
 
===Urinary System===
 
===Urinary System===
−
 
+
'''Kidneys'''
−
===Respiratory System===
+
<br />
−
 
+
Extremely long papillae extending into ureters. Very developed water conservation systems.
 +
<br />
 +
===Cardio-Respiratory System===
 +
'''Heart'''
 +
<br />
 +
The Purkinje network and sino-atrial node are easily accessible surgically and is a useful physiological feature for some experiments.
 +
<br />
 
===Digestive System===
 
===Digestive System===
−
 
+
'''Cheek Pouches'''
 +
<br />
 +
Hamsters have highly distensible evaginations of the lateral buccal walls which are used to store and transport food.
 +
<br />
 +
<br />
 +
'''GI Physiology'''
 +
<br />
 +
Long duodenum, long jejunum, short ileum, big cecum, long colon.
 +
<br />
 +
<br />
 +
'''Stomach'''
 +
<br />
 +
Distinct constriction between the forestomach and glandular stomach. No lesser curvature of the stomach resulting in two blind sacs. Pregastric fermentation occurs in hamsters.
 +
<br />
 +
<br />
 +
'''Cecum'''
 +
<br />
 +
Apical an basal portions seperated by a semilunar valve. There are a series of 4 valves in the ileocecolic area.
 +
<br />
 +
<br />
  
 
==Diseases==
 
==Diseases==
 
For ease of use, the diseases of hamsters listed below are by body system, or where this is not appropriate in an “Other” category displayed after the body system sections. Those diseases listed below are not exhaustive but rather highlight common diseases encountered with laboratory hamsters.
 
For ease of use, the diseases of hamsters listed below are by body system, or where this is not appropriate in an “Other” category displayed after the body system sections. Those diseases listed below are not exhaustive but rather highlight common diseases encountered with laboratory hamsters.
 +
<br />
  
 
==Integument System==
 
==Integument System==
−
 
−
 
−
===Dermatitis===
 
−
 
−
 
 
===Dermatophytosis (Ringworm)===
 
===Dermatophytosis (Ringworm)===
−
 
+
Fungal infections occur infrequently in hamsters. [[Dermatophytosis|''Trichophyton mentagrophytes'']] and [[Dermatophytosis|''microsporum spp'']] are the most commonly isolated. In Infection may be asymptomatic or show clinical signs including small, patchy alopecia.
 +
<br />
 +
Macroscopic pathology includes irregular to circular, crusty, flaky skin lesions with reddened margins.
 +
<br />
  
 
===Mange===
 
===Mange===
 +
The mites [[Demodex|''Demodex criceti'']] and [[Demodex|''Demodex aurati'']] can have a reasonably high infestation level without clinical signs. Both mites are often found together, although ''Demodex criceti'' is considered to be non-pathogenic. Increased incidence has been reported in males an older animals and also as a secondary condition to malnutrition or concurrent disease.
 +
<br />
 +
Clinical signs range from none to alopecia, scaly skin, dermatitis and a rough looking coat. Alopecia generally occurs over the rump and back.
 +
<br />
  
−
===Lice===
 
 
===Other Mite Infestations===
 
===Other Mite Infestations===
−
 
+
Other species of mite reported in hamsters include [[Sarcoptes|''Sarcoptes scabei'']], [[Notoedres|''Notoedres spp'']] (ear mite), ''Speleorodens clethrionomys'' (nasal mite) and ''Ornithonyssus bacoti'' (tropical rat mite).
−
===Fly Strike===
+
<br />
−
 
 
−
===Alopecia===
 
−
 
 
−
===Liver Disease===
 
  
 
===Abscesses===
 
===Abscesses===
−
 
+
Skin abcesses are often caused by trauma including fighting. [[Staphylococcus_aureus|''Staphylococcus aureus'']], ''Streptococcus spp.'', [[Pasteurella_pneumotropica|''Pasturella pneumotropica'']] and ''Actinomyces aureus'' have been isolated from skin abcesses.
 +
<br />
  
 
==Reproductive System==
 
==Reproductive System==
−
===Pseudopregnancy===
+
===Reproductive Tract Neoplasms===
−
 
+
This condition most commonly occurs mainly in female syrian hamsters with risk increasing with age.
−
===Pregnancy toxaemia===
+
<br />
−
 
+
Uterine carcinomas are seen in 25% of female neoplasm cases.
−
 
+
<br />
−
===Hypocalcemia (Eclampsia)===
 
−
 
 
−
===Miscarriage and Abortion===
 
−
 
 
−
===Toxoplasmosis===
 
−
 
 
 
===Mastitis===
 
===Mastitis===
−
 
+
Acute bacterial mastitis has been associated with opportunistic infections of β-haemolytic ''Streptococcus spp.'' and usually occuring 7-10 days post parturition.
−
===Preputial infections===
+
<br />
 +
Macroscopic pathology will include swollen mammary glands and in some cases a mucopurulent exudate. Some females suffering with mastitis may cannabalise their litters.
 +
<br />
  
 
==Urinary System==
 
==Urinary System==
−
===Polydipsia===
+
===Amyloidosis===
 +
[[Amyloidosis|Amyloidosis]] causes soluable proteins to polymerise into insoluable fibrils resulting in chronic infections and impaired renal function. This condition frequently in older (>1) female hamsters.
 +
<br />
 +
Macroscopic histology includes rough, pale and enlarged kidneys, enlarged adrenal glands and liver at necropsy. Microscopic histopathology may include glomerular hyalinisation, amyloid deposits in tubules and amyloid deposits in other organs including the spleen, liver and adrenals. Microscopic histopathology can be easily visualised with Congo red stain.
 +
<br />
  
−
===Polyuria===
+
===Arteriolar Nephrosclerosis (Hamster Nephrosis)===
−
 
+
Arteriolar nephrosclerosis is a degenerative disease occurring most commonly in older hamsters, particularly females. Clinical symptoms will include weight loss and polyuria/polydipsia. Some links have been made between this disease and 'Lymphocytic choriomeningitis' virus infections (see below) which results in renal vascular hypertension. Arteriolar nephrosclerosis may also be concurrent with amyloidosis (above).
−
===Haematuria===
+
<br />
−
 
+
Macroscopic pathology on necropsy will include irregular kidneys that may be granular or pitted in appearance. Microscopic histopathology will include interstitial fibrosis, basement membrane thickening, tubular dilation with proteinaceous exosinophilic material and renal casts.
−
===Acute Renal Failure===
+
<br />
−
 
+
===Diabetes Mellitus===
−
===Chronic Renal Failure===
+
Known to occur spontaneously in some inbred strains of Chinese hamster, inherited via a recessive gene. Clinical symptoms include weight loss, glucose intolerance, mild to severe hyperglycemia, polydipsia, polyuria, hypoinsulinemia and ketouria.
−
 
+
<br />
−
===Diabetes===
+
Microscopic pathology will include pancreatic islet involution with severe and widespread nuclear pyknotic (irreversible condensation of chromatin in the nucleus of a cell undergoing necrosis or apoptosis), shrunken and eosinophilic cytoplasm with cytoplasmic vacuoles and loss of granules.
 +
<br />
  
 
==Respiratory System==
 
==Respiratory System==
−
===Epistaxis===
+
===Pneumonia===
 +
Although pneumonia is relatively uncommon in hamsters, it can be caused by a number of bacterial pathogens including ''Streptococcus pneumoniae, S. agalactiae, Pasturella pneumotropica, Staphylococcus aureus, [[Klebsiella|Klebsiella pneumoniae]], [[Bordetella_species_-_Overview|Bordetella spp]], [[Corynebacterium_species_-_Overview|Corynebacterium paulometabulum]]'' and [[Salmonella|''Salmonella spp.'']].
 +
<br />
 +
Macroscopic pathology includes respiratory lesions at necropsy.
 +
<br />
  
 +
==Cardiovascular System==
 +
===Atrial Thrombosis===
 +
[[Atrial_Thrombosis|Atrial thrombosis]] and congestive heart failure are associated with older female hamsters and occur frequently. Atrial thrombosis is also associated with amyloidosis (see above). Clinical symptoms include dyspnea, tachycardia and cyanosis.
 +
<br />
 +
Macroscopic pathology will display a thrombi most commonly in the left atria.
 +
<br />
  
 
==Digestive System==
 
==Digestive System==
−
===Cytomegalovirus (Salivary Gland Virus)===
+
===Parvoviral Infection===
−
CMV often causes subclinical infections and associated immunosupression. CMV is transmitted via the placenta. <br />
+
This is an epizootic infection with a high mortality resulting in malformed and missing incisors and is mainly observed among suckling and weaning pups in Syrian hamsters.
−
Microscopic pathology will include the appearence of eosinophilic intranuclear inclusion bodies which are often accompanied by basophilic cytoplasmic inclusions in the ductal epithelial cells of the salivary glands. In some cases there is also a a lymphoid cell infiltrate.
 
 
<br />
 
<br />
−
===Infectious Causes of Diarrhoea===
+
Macroscopic pathology will include necrosis and inflammation of the dental pulp with mononuclear leukocytic infiltration of the dental lamina and osteoclasis of the alveolar bone.
−
'''Salmonella'''
 
 
<br />
 
<br />
−
''Salmonella typhimurium'' and ''Salmonella enteriditis'' are the common causative agents and are often associated with contaminated food and bedding. Diarrhoea may be haemorrhagic, cause septicaemia and can also cause sudden death.  
+
===Enteritis===
 +
Also called 'wet tail'. Enteritis occurs most frequently in 2-3 week old hamsters and results primarily from colonisation of pathogenic bacteria but may signal one of several GI diseases. Enteritis is one of the most common and serious diseases found in laboratory hamsters and has between 20-60% morbidity and up to 90% mortality.  
 
<br />
 
<br />
−
Macroscopic pathologic findings include enlarged liver, spleen, intestine and lymph nodes containing small white necrotic foci in chronically infected animals. Pregnant animals may have a purulent metritis. There may also be hyperplasia in the Peyer's patch and splenomegally. Microscopically there may be granulomatous hepatitis, splenitis and lymphadenitis with the areas of necrosis are surrounded by mononuclear cells and neutrophils.  
+
General macroscopic pathology includes ileal thickening and enlargement at the terminal portion with roughened and reddened mucosa and serosa, enlarged mesenteric lymph nodes, peritonitis, flaccid cecum with fetid watery contents and abdominal adhesions. In very advanced cases, small white spots are visible within the ileum together with serosal nodules.  
 
<br />
 
<br />
−
There are often no findings in animals with acute infections.
+
Microscopic histopathology will include hyperplasia of the crypt epithelial cells, migration of immature epithelium into the villi, downward extension of the crypts through the lamina propria, muscularis mucosa, submucosa, Peyer's patches, muscularis externa and serosa. There will be necrosis of epithelial cells to a varying degree with haemorrhage, pyogranulomatous inflammation and crypt microabcesses.
 +
<br />
 +
 
 +
===Infectious Causes of Enteritis===
 +
'''Clostridial Enteritis'''
 +
<br />
 +
''Clostridium perfringens, [[C._difficile|C. difficile]]'' and ''C. spiroforme'' produce toxins causing oedema, haemorrhage, mucosal dysfunction and necrosis. Clostridial enteritis manifests as 2 syndromes. The first is acute diarrhoea that is likely to have been caused by dietary changes, antibiotic therapy, concurrent diseases or physiological stresses. The second manifestation occurs in older (>6months) hamsters where they slowly loose weight and condition and die without diarrhoea.<br />
 +
Acute diarrhoea is macroscopically diagnosed at necropsy by serosal and mucosal haemorrhages of the cecum and sometimes the lower intestine. Definitive diagnosis for either manifestation is made via bacterial culture. The second manifestation is diagnosed macroscopically via a thickening of the cecal wall containing inflammatory cell infiltrate.
 +
<br />
 +
<br />
 +
'''Colibacillosis'''
 +
<br />
 +
''E. coli'' is transmitted via direct contact, fecal-oral and fomite transmission. Predisposing factors include a high carbohydrate diet, stress, overcrowding and lack of fresh water. Clinical signs include yellow watery diarrhoea that mats around the tail.
 +
<br />
 +
Microscopic pathology includes lesions in the small intestine and cecum together with serosal oedema. There will also be submucosal oedema and effacement of enterocytes colonised by bacteria in the small intestine or cecum. Often there is no inflammatory cell inflitrate in the lamina propria or submucosa.
 +
<br />
 +
<br />
 +
'''Ileitis'''
 +
<br />
 +
Causative agents include ''Campylobacter coli'', [[Campylobacter_fetus_subspecies_fetus|''Campylobacter fetus'']] and chlamydial organisms transmitted via fecal-oral or fomite contamination. Clinical signs include lethargy, anorexia, diarrhoea, dehydration and death. Moist faeces often stains the base of the tail. Ileitis primarily occurs in hamsters of between 3 to 10 weeks.
 +
<br />
 +
Macroscopic pathology will include yellow to dark red fluid within the small intestine and mesenteric lymph node hyperplasia. There may also be focal coagulative necrosis in the liver.  
 
<br />  
 
<br />  
−
Diagnosis is via isolation and culture of the ''Salmonella spp'' via faecal samples.<br />
+
Microscopic pathology includes lesions in the ileum and cecum and serosal haemorrhage. The ileum is often also thickened. Intestinal segments will have mild to moderate segmental hyperplasia of the mucosa. Intestinal crypts will appear elongated with marked proliferation of enterocytes and often goblet cells. Lymphoid hyperplasia may be seen together with leukocytes near the base of the villi. Diagnosis is primarily made via histolology.
−
Chronic cases and those that recover from a ''Salmonella'' infection are likely to become carriers and should be destroyed to prevent further outbreaks. <br />
 
−
'''Yersinia (pseudotuberculosis)'''
 
 
<br />
 
<br />
−
Acute forms of this disease can cause septicaemia and death within 48hrs. Chronic cases have more progressive clinical symptoms but will usually culminate in death after 3-4 weeks. During this 3-4 week period any young may become congenitally or neonatally affected. Diagnosis is via culture of ''Yersinia pseudotuberculosis'' from blood, lymph nodes or faecal samples.<br />
 
−
''Yersinia'' infections are transmitted via wild birds and other rodents contaminating their food, particularly green foods. Once the disease is endemic  in a breeding population some infections can be passed vertically in the milk. Macroscopic pathologic lesions include enlarged or abscessed lymph nodes and necrosis of liver and spleen.<br />
 
−
'''Clostridia'''
 
 
<br />
 
<br />
−
Normally this species are present in the large intestines as commensals but during certain circumstances such as antibiotic administration they are able to proliferate and cause fatal enterotoxaemia. ''Clostridium'' species can be cultured from the lumen of the infected intestine.
+
'''Salmonellosis'''
 
<br />
 
<br />
−
Pathologic examination will show necrotizing ileitis and typhlitis. Hepatic lesions may be present and will be characterized by focal coagulative necrosis in periportal regions.
+
The incidence of salmonellosis in hamsters is low. [[Salmonella|''Salmonella enterica'']] is the common causative agent and is associated with contaminated food and bedding. Diarrhoea may be haemorrhagic, cause septicaemia and can also cause sudden death. Clinical signs are primarily seen in pregnant females or infants.  
 
<br />
 
<br />
−
'''Antibiotic-Induced Enterotoxemia'''
+
Macroscopic pathology includes fluid filled small intestine and cecum. The lungs may have a patchy haemorrhagic appearence. Small white foci are visible in the liver. The most significant macroscopic pathology is a septic lesion partially occluding thrombosis of pulmonary venules. Multifocal necrosis of the liver, lymph nodes and spleen may also be visible.
 
<br />
 
<br />
−
Bacterial overgrowth is associated with enterocolitis, septicemia and death.  Antibiotics implicated include penicillin, erythromycin, lincomycin, chlortetracycline, oxytetracycline, bacitracin, dihydrostreptomycin, cefazolin, cephalexin, cephalothin, ampicillin, clindamycin & gentamycin. All of the above species have been implicated as potential causative agents.
 
 
<br />
 
<br />
−
Macroscopic pathology during necropsy will include a distended cecum containing blood and hemorrhagic serosal and mucosal surfaces. Microscopic pathology during necropsy will include extensive vascular congestion, submucosal hemorrhage and oedema, and sloughing of the absorptive epithelium throughout the GI tract.
+
'''Tyzzer's Disease'''
 +
<br>
 +
This is caused by [[Clostridium_piliforme|''clostridium piliforme'']]. Infected hamsters exhibit a hunched posture and rough hair coats with or without diarrhoea.
 +
<br />
 +
Macroscopic pathology is widespread and includes enterocolitis with oedema, hyperemia of the large intestines, lymphadenitis and multifocal liver necrosis.
 
<br />
 
<br />
  
−
===Parasitic Causes of Diarrhoea===
+
===GI Parasites===
−
'''Nematodes'''
+
'''Nematodes (Pinworms)'''
 
<br />
 
<br />
−
The only nematode that affects guinea pigs is Paraspidodera uncinata and is usually restricted to outdoor housed animals. Heavy infestation can cause  enteritis and the Paraspidodera resides in the caecum and can be 11-28mm long. <br />
+
The hamster pinworms ''Syphacia mesocricetus'', ''syphacia obvelata'' and ''syphacia muris'' are capable of inflicting heavy parasitic loads, although incidence of infection is low. Transmisson of infection occurs through ova ingetion and the eggs have also been shown to aerosolise increasing potential infection risks.
−
'''Protozoa'''
 
 
<br />
 
<br />
−
A wide range of commensal protozoa are carried and are not pathogenic except for Coccidia and Cryptosporidium species. Protozoan infections are generally the result of poor husbandry. Contact with rabbits can allow other rare protozoan infections in guinea pigs. <br />
+
Heavy parasitic loads may lead to rectal prolapse or perianal irritation. Macroscopic pathology will show thickened GI tract and pinworms are recognised as white hair-like nematodes in the cecum.
−
Eimeria caviae is the coccidial species contracted by guinea pigs eating contaminated food, however coccidiosis in guinea pigs is rare. Droppings will be slimy and contain blood. Oocysts will be present in the faeces and can be seen on microscopic examination.<br />
 
−
Cryptosporidium species that colonise the intestine will cause weight loss and diarrhoea.
 
 
<br />
 
<br />
−
Microscopic pathologic findings will include flattened and irregular villi in the ileum together with a granulomatous infiltrate into the lamina propria and absorptive areas of the intestinal epithelium. In some cases the parasite itself may be visualised via parasitophorous vacuoles within the apical portion of the infected enterocyte.
 
 
<br />
 
<br />
−
'''Ascaridae'''
+
'''Cestodes'''
 +
<br />
 +
''Rodentolepis nana'' (dwarf tapeworm) or ''Hymenolepis diminuta'' are common although usually asymptomatic. Heavy infections may cause enteritis, intestinal impaction and abcesses within the mesentric lymph nodes.
 +
<br />
 +
Macroscopic pathology will show thickened and inflamed intestines.
 +
<br />
 +
 
 +
==Other==
 +
===Tularemia===
 +
Although this is rarely reported in hamsters, [[Francisella_tularensis|''Francisella tularensis'']] causes acute septicemia and has a high morbidity and mortality rates. Death occurs with 48hrs of onset.
 +
<br />
 +
Macroscopic pathology includes haemorrhagic lungs, enlarged and necrotic liver and spleen, prominent Peyer's patches and enlarged mesenteric lymph nodes.
 +
<br />
 +
This is a zoonotic pathogen.
 
<br />
 
<br />
−
Ascaridae are not a natural parasite of guinea pigs but if housed outdoors in areas which has been contaminated with dog or cat faeces guinea pigs will suffer from weight loss, unthriftiness and diarrhoea.<br />
 
  
−
==Musculoskeletal System==
+
===Yersiniosis (Pseudotuberculosis)===
−
===Pododermatitis===
+
[[Yersinia_pseudotuberculosis|''Yersinia pseudotuberculosis'']] is usually the result of fecal contamination of food or water and leads to acute septicemia and intermittent diarrhoea.  
−
The origin of the swelling and ulceration of the foot pad is usually bacterial, most commonly Staphylococcus aureus. Treatment of advanced infections is rarely successful. <br />
+
<br />
−
===Osteoporosis===
+
Macroscopic pathology includes lesions in the mesenteric lymph nodes, spleen, liver, lungs, gallbladder and intestinal walls.
−
This condition will occur if guinea pigs are over-supplemented with vitamin D via forced such as cod-liver oil. The excess vitamin D leads to excess calcium resorption and subsequent bone weakness. Clinical signs are usually paralysis and most commonly seen in the hind legs first. <br />
+
<br />
−
The diet should contain a maximum of 1600iu of vitamin D per kg.<br />
 
−
===Metastatic Calcification===
 
−
This condition is caused by an imbalance between calcium, phosphrous and vitamin D. Metastatic calcification is mainly seen in males in which they exhibit joint stiffness, poor weight gain and eventually death.  <br />
 
−
Macroscopic pathology will show mineralisation/calcification of the heart, blood vessels, stomach, colon, kidneys and lungs.<br />
 
−
The diet should have a calcium:phosphorus ratio of 1:5 and the same vitamin D level as above. <br />
 
  
−
===Scurvy===
+
===Cholangiofibrosis===
−
This condition is due to a deficiency of vitamin C where an adult guinea pig requires 10-30mg per day.  
+
Also called cholangiohepatitis, the cause of this pathology is thought to be from a [[Helicobacter|Helicobacter]] species called ''H. cholecysticus''. Affected hamsters display no clinical signs.
 +
<br />
 +
Macroscopic pathology includes bile duct hyperplasia, pericholangial fibrosis and centrilobular pancreatitis.
 
<br />
 
<br />
−
Macroscopic pathology will include haemorrhages around joints and on all serosal surfaces, particularly around fascial and articular cartilages. Petechial and ecchymotic bleeding may be seen  on the periosteum, muscle and gingiva.<br />
 
  
−
===Osteoarthritis===
+
===Lymphocytic Choriomeningitis Virus (LCM)===
−
In guinea pigs the most commonly affected joint is the stifle and clinical symptoms can range from lameness to weight loss in guinea pigs of 9 months and older.<br />
+
LCM is an RNA virus from the arenavirus group and is rare in hamsters, although most reported human cases have been associated with infected hamsters. ''In utero'' or perinatal infections may facilitate chronic infection resulting in a progressive wasting disease affecting the liver, spleen, lung, meningies and brain. Approximately 50% of hamsters will clear the infection.
−
===Osteosarcoma===
 
−
Although relatively uncommon in guinea pigs they can be seen as painful bony swellings in guinea pigs over 1 ear of age.<br />
 
−
==Other==
 
−
===Micropthalmia===
 
−
The eye will either appear small or will be non-existant with resultant partial or complete blindness. Micropthalmia is commonly associated with all-white coated guinea pigs.<br />
 
−
===Conjunctivitis===
 
−
The conjunctiva will become reddened with epiphora or an ocular discharge. Often conjunctivitis is either a symptom of upper respiratory disease, irritation and allergic response. If the conjunctivitis is unilateral then trauma is likely to be the cause.<br />
 
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===Middle Ear Disease===
 
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The affected guinea pig will hold its head over to the affected side and may also suffer balance problems. The condition is very similar in terms of symptoms to “wry neck”, see below. Pus may be seen in the ear canal and the infection may progress to the inner ear and to the meninges. Ear infections in guinea pigs are also known to accompany respiratory infections such as Salmonella and Pasturella spp. <br />
 
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===Cleft Palate===
 
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This is a congenital abnormality resulting in the guinea pig potentially being unable to suckle or chew food correctly. In guinea pigs the cleft usually involves the hard palate only. There is no treatment and do to its inherited nature the guinea pig should be destroyed.<br />
 
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===Cervical Lymphadenitis===
 
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Steptococcus zooepidemicus is normally present in the conjunctiva as a commensal organism. If this organism gains access to the cervical lymph nodes they can become pathogenic and in some cases death can occur due to septicaemia. Infection will cause the lymph nodes to swell. Stress has been shown to increase susceptibility. <br />
 
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Necropsy will show macroscopic pathology ranging from enlarged ventral and cervical lymph nodes to  encapsulated abscesses filled with a thick yellow/white purulent exudate. Associated pathology found in other organ systems involved may include bronchopneumonia, otitis media, pleuritis, peritonitis, and pericarditis. Infection may vary from an acute fatal septicemia to a chronic suppurative process in the lymph nodes, thoracic and abdominal viscera, uterus, and ears.
 
 
<br />
 
<br />
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Microscopic evidence of pneumonia, pleuritis, myocarditis, pericarditis, and peritonitis, otitis media, nephritis, arthritis, and cellulitis will be seen characterized by necrotizing suppurative inflammation or fibrinosuppurative inflammation.
+
A common route of infection of LCM in research laboratories is via the transplantation of LCM-containing tumours. Macroscopic pathology may include splenomegally, swollen or shrunken pitted kidneys and hepatomegally. Microscopic pathology may include lymphocytic meningitis, chronic glomerulonephropathy, widespread vasculitis and widespread lymphocytic infiltration.
 
<br />
 
<br />
  
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===Wry Neck===
+
 
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This condition affects only newborn guinea pigs in which they have a degree of torticollis and may be found lying on their backs to suckle due to their inability to maintain a suitable head posture. This condition is hereditary.<br />
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[[Category:Laboratory Animal Pathology]]
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===Epilepsy===
 
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Guinea pig epileptic fits usually last for 3 to 4 mins where there will be heavy salivation and twitching of limbs. Polyphagia and aggression can be seen post-fit. Commonly the frequency of fits will increase with age.<br />
 
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Guinea pigs also have fits that are not true epileptiform convulsions and are often secondary to another disease. These can include liver and kidney failure, enterotoxaemia, ketosis and septicaemia.<br />
 
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===Cerebellar Disease===
 
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Classical symptoms of this disease are circling movements, dystocia and nystagmus, although nystagmus is rare in guinea pigs. In most cases cerebellar disease is secondary to the above mentioned middle ear infection progressing to the inner ear. Most guinea pigs do not recover from this even with treatment.<br />
 
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===Heatstroke===
 
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Although this can occur in outdoor guinea pigs exposed to direct sunlight, heavily pregnant females are the most susceptible especially if they have been deprived of water. This can be a problem during transportation or during problems with laboratory infrastructures such as air conditioning.<br />
 

Latest revision as of 15:43, 15 February 2011

Introduction

Hamsters are now commonly used in laboratory testing, but for many years other species including mice, rats and guinea pigs were used for studies requiring small easily managed animals. In 1919 the first study using hamsters was undertaken assessing the susceptibility of Chinese hamsters to leishmania. A number of difficulties were encountered including an inability to breed the animals and hamsters were not used again until the 1930s when a Syrian hamster burrow was uncovered by an archaeologist near Aleppo. Nearly all common golden hamster breeds are related to these wild discovered hamsters. Syrian hamsters (Mesocricetus auratus)were used and were found to be easier to breed and had more desirable traits for laboratory testing than Chinese hamsters. Syrian hamsters have gone on to become the most commonly encountered laboratory hamster species with around 500,000 per year currently used in the US. However, approximately ten times more mice and rats are used compared to hamsters.

Strains and Stocks

Although Syrian hamsters Mesocricetus auratus or Golden hamsters are the most commonly encountered laboratory species, a number of other species are also used. These include the Chinese hamster Cricetus cricetus, the Armenian hamster Cricetulus migratorius, the Dzungarian hamster Phodopus sungarus and the South African hamster Mystromyx albicauafus. There are a number of differences between these types of hamster;

Breed Description
Syrian/Golden Compact body, short legs, 4 front toes, 5 rear toes, 120g, approximately 15cm long, short tail, dark ears, females larger than males.
Chinese usually grey with a black stripe down its back, 30-35g.
European usually has a black bely
Dzungarian varieties include siberian, dwarf, striped and hairyfooted. 30-35g. Summer coat is brown and winter is white.
South African usually white tailed.

Physiology

Please find details of hamster physiology within the WikiNormals section. Physiological information available includes “General”, “Biochemical”, “Haematological” and “Breed” parameters.

General Behavioural Characteristics

In particular, Syrian hamsters are solitary and only tolerate company when breeding. Females are easily disturbed and aggressive when lactating or pregnant and in such situations, can be prone to kill other hamsters. Cannibalism is common in stressed primiperous females. Chinese hamsters are particularly pugilistic.

Anatomy and Histology

This section has been included to allow familiarisation with the peculiarities of hamster anatomy to provide a context for some of the disease and pathological headings found below. Therefore only anatomical areas with specific features warranting emphasis have been included below;

Integumentary System

Hip/Flank Glands
Sebaceous glands with pigmented cells and terminal hairs that secrete during sexual arounsal in both sexes. Also used for olfactory territorial marking.

Reproductive System

Vaginal Discharge
Post-ovulatory dimethyl disulphide is used as a breeding tool by females but is often mistaken for an inflammatory exudate due to its similarity in smell to rotten eggs.

Sexual Dimorphism
Male Syrian hamsters have much larger adrenal glands than females despite females being generally larger than males.

Fostering Newborn
This is not usually possible in hamsters as infants are extremely immature when born and 'foreign' infants usually do not accept one another.

Urinary System

Kidneys
Extremely long papillae extending into ureters. Very developed water conservation systems.

Cardio-Respiratory System

Heart
The Purkinje network and sino-atrial node are easily accessible surgically and is a useful physiological feature for some experiments.

Digestive System

Cheek Pouches
Hamsters have highly distensible evaginations of the lateral buccal walls which are used to store and transport food.

GI Physiology
Long duodenum, long jejunum, short ileum, big cecum, long colon.

Stomach
Distinct constriction between the forestomach and glandular stomach. No lesser curvature of the stomach resulting in two blind sacs. Pregastric fermentation occurs in hamsters.

Cecum
Apical an basal portions seperated by a semilunar valve. There are a series of 4 valves in the ileocecolic area.

Diseases

For ease of use, the diseases of hamsters listed below are by body system, or where this is not appropriate in an “Other” category displayed after the body system sections. Those diseases listed below are not exhaustive but rather highlight common diseases encountered with laboratory hamsters.

Integument System

Dermatophytosis (Ringworm)

Fungal infections occur infrequently in hamsters. Trichophyton mentagrophytes and microsporum spp are the most commonly isolated. In Infection may be asymptomatic or show clinical signs including small, patchy alopecia.
Macroscopic pathology includes irregular to circular, crusty, flaky skin lesions with reddened margins.

Mange

The mites Demodex criceti and Demodex aurati can have a reasonably high infestation level without clinical signs. Both mites are often found together, although Demodex criceti is considered to be non-pathogenic. Increased incidence has been reported in males an older animals and also as a secondary condition to malnutrition or concurrent disease.
Clinical signs range from none to alopecia, scaly skin, dermatitis and a rough looking coat. Alopecia generally occurs over the rump and back.

Other Mite Infestations

Other species of mite reported in hamsters include Sarcoptes scabei, Notoedres spp (ear mite), Speleorodens clethrionomys (nasal mite) and Ornithonyssus bacoti (tropical rat mite).

Abscesses

Skin abcesses are often caused by trauma including fighting. Staphylococcus aureus, Streptococcus spp., Pasturella pneumotropica and Actinomyces aureus have been isolated from skin abcesses.

Reproductive System

Reproductive Tract Neoplasms

This condition most commonly occurs mainly in female syrian hamsters with risk increasing with age.
Uterine carcinomas are seen in 25% of female neoplasm cases.

Mastitis

Acute bacterial mastitis has been associated with opportunistic infections of β-haemolytic Streptococcus spp. and usually occuring 7-10 days post parturition.
Macroscopic pathology will include swollen mammary glands and in some cases a mucopurulent exudate. Some females suffering with mastitis may cannabalise their litters.

Urinary System

Amyloidosis

Amyloidosis causes soluable proteins to polymerise into insoluable fibrils resulting in chronic infections and impaired renal function. This condition frequently in older (>1) female hamsters.
Macroscopic histology includes rough, pale and enlarged kidneys, enlarged adrenal glands and liver at necropsy. Microscopic histopathology may include glomerular hyalinisation, amyloid deposits in tubules and amyloid deposits in other organs including the spleen, liver and adrenals. Microscopic histopathology can be easily visualised with Congo red stain.

Arteriolar Nephrosclerosis (Hamster Nephrosis)

Arteriolar nephrosclerosis is a degenerative disease occurring most commonly in older hamsters, particularly females. Clinical symptoms will include weight loss and polyuria/polydipsia. Some links have been made between this disease and 'Lymphocytic choriomeningitis' virus infections (see below) which results in renal vascular hypertension. Arteriolar nephrosclerosis may also be concurrent with amyloidosis (above).
Macroscopic pathology on necropsy will include irregular kidneys that may be granular or pitted in appearance. Microscopic histopathology will include interstitial fibrosis, basement membrane thickening, tubular dilation with proteinaceous exosinophilic material and renal casts.

Diabetes Mellitus

Known to occur spontaneously in some inbred strains of Chinese hamster, inherited via a recessive gene. Clinical symptoms include weight loss, glucose intolerance, mild to severe hyperglycemia, polydipsia, polyuria, hypoinsulinemia and ketouria.
Microscopic pathology will include pancreatic islet involution with severe and widespread nuclear pyknotic (irreversible condensation of chromatin in the nucleus of a cell undergoing necrosis or apoptosis), shrunken and eosinophilic cytoplasm with cytoplasmic vacuoles and loss of granules.

Respiratory System

Pneumonia

Although pneumonia is relatively uncommon in hamsters, it can be caused by a number of bacterial pathogens including Streptococcus pneumoniae, S. agalactiae, Pasturella pneumotropica, Staphylococcus aureus, Klebsiella pneumoniae, Bordetella spp, Corynebacterium paulometabulum and Salmonella spp..
Macroscopic pathology includes respiratory lesions at necropsy.

Cardiovascular System

Atrial Thrombosis

Atrial thrombosis and congestive heart failure are associated with older female hamsters and occur frequently. Atrial thrombosis is also associated with amyloidosis (see above). Clinical symptoms include dyspnea, tachycardia and cyanosis.
Macroscopic pathology will display a thrombi most commonly in the left atria.

Digestive System

Parvoviral Infection

This is an epizootic infection with a high mortality resulting in malformed and missing incisors and is mainly observed among suckling and weaning pups in Syrian hamsters.
Macroscopic pathology will include necrosis and inflammation of the dental pulp with mononuclear leukocytic infiltration of the dental lamina and osteoclasis of the alveolar bone.

Enteritis

Also called 'wet tail'. Enteritis occurs most frequently in 2-3 week old hamsters and results primarily from colonisation of pathogenic bacteria but may signal one of several GI diseases. Enteritis is one of the most common and serious diseases found in laboratory hamsters and has between 20-60% morbidity and up to 90% mortality.
General macroscopic pathology includes ileal thickening and enlargement at the terminal portion with roughened and reddened mucosa and serosa, enlarged mesenteric lymph nodes, peritonitis, flaccid cecum with fetid watery contents and abdominal adhesions. In very advanced cases, small white spots are visible within the ileum together with serosal nodules.
Microscopic histopathology will include hyperplasia of the crypt epithelial cells, migration of immature epithelium into the villi, downward extension of the crypts through the lamina propria, muscularis mucosa, submucosa, Peyer's patches, muscularis externa and serosa. There will be necrosis of epithelial cells to a varying degree with haemorrhage, pyogranulomatous inflammation and crypt microabcesses.

Infectious Causes of Enteritis

Clostridial Enteritis
Clostridium perfringens, C. difficile and C. spiroforme produce toxins causing oedema, haemorrhage, mucosal dysfunction and necrosis. Clostridial enteritis manifests as 2 syndromes. The first is acute diarrhoea that is likely to have been caused by dietary changes, antibiotic therapy, concurrent diseases or physiological stresses. The second manifestation occurs in older (>6months) hamsters where they slowly loose weight and condition and die without diarrhoea.
Acute diarrhoea is macroscopically diagnosed at necropsy by serosal and mucosal haemorrhages of the cecum and sometimes the lower intestine. Definitive diagnosis for either manifestation is made via bacterial culture. The second manifestation is diagnosed macroscopically via a thickening of the cecal wall containing inflammatory cell infiltrate.

Colibacillosis
E. coli is transmitted via direct contact, fecal-oral and fomite transmission. Predisposing factors include a high carbohydrate diet, stress, overcrowding and lack of fresh water. Clinical signs include yellow watery diarrhoea that mats around the tail.
Microscopic pathology includes lesions in the small intestine and cecum together with serosal oedema. There will also be submucosal oedema and effacement of enterocytes colonised by bacteria in the small intestine or cecum. Often there is no inflammatory cell inflitrate in the lamina propria or submucosa.

Ileitis
Causative agents include Campylobacter coli, Campylobacter fetus and chlamydial organisms transmitted via fecal-oral or fomite contamination. Clinical signs include lethargy, anorexia, diarrhoea, dehydration and death. Moist faeces often stains the base of the tail. Ileitis primarily occurs in hamsters of between 3 to 10 weeks.
Macroscopic pathology will include yellow to dark red fluid within the small intestine and mesenteric lymph node hyperplasia. There may also be focal coagulative necrosis in the liver.
Microscopic pathology includes lesions in the ileum and cecum and serosal haemorrhage. The ileum is often also thickened. Intestinal segments will have mild to moderate segmental hyperplasia of the mucosa. Intestinal crypts will appear elongated with marked proliferation of enterocytes and often goblet cells. Lymphoid hyperplasia may be seen together with leukocytes near the base of the villi. Diagnosis is primarily made via histolology.

Salmonellosis
The incidence of salmonellosis in hamsters is low. Salmonella enterica is the common causative agent and is associated with contaminated food and bedding. Diarrhoea may be haemorrhagic, cause septicaemia and can also cause sudden death. Clinical signs are primarily seen in pregnant females or infants.
Macroscopic pathology includes fluid filled small intestine and cecum. The lungs may have a patchy haemorrhagic appearence. Small white foci are visible in the liver. The most significant macroscopic pathology is a septic lesion partially occluding thrombosis of pulmonary venules. Multifocal necrosis of the liver, lymph nodes and spleen may also be visible.

Tyzzer's Disease
This is caused by clostridium piliforme. Infected hamsters exhibit a hunched posture and rough hair coats with or without diarrhoea.
Macroscopic pathology is widespread and includes enterocolitis with oedema, hyperemia of the large intestines, lymphadenitis and multifocal liver necrosis.

GI Parasites

Nematodes (Pinworms)
The hamster pinworms Syphacia mesocricetus, syphacia obvelata and syphacia muris are capable of inflicting heavy parasitic loads, although incidence of infection is low. Transmisson of infection occurs through ova ingetion and the eggs have also been shown to aerosolise increasing potential infection risks.
Heavy parasitic loads may lead to rectal prolapse or perianal irritation. Macroscopic pathology will show thickened GI tract and pinworms are recognised as white hair-like nematodes in the cecum.

Cestodes
Rodentolepis nana (dwarf tapeworm) or Hymenolepis diminuta are common although usually asymptomatic. Heavy infections may cause enteritis, intestinal impaction and abcesses within the mesentric lymph nodes.
Macroscopic pathology will show thickened and inflamed intestines.

Other

Tularemia

Although this is rarely reported in hamsters, Francisella tularensis causes acute septicemia and has a high morbidity and mortality rates. Death occurs with 48hrs of onset.
Macroscopic pathology includes haemorrhagic lungs, enlarged and necrotic liver and spleen, prominent Peyer's patches and enlarged mesenteric lymph nodes.
This is a zoonotic pathogen.

Yersiniosis (Pseudotuberculosis)

Yersinia pseudotuberculosis is usually the result of fecal contamination of food or water and leads to acute septicemia and intermittent diarrhoea.
Macroscopic pathology includes lesions in the mesenteric lymph nodes, spleen, liver, lungs, gallbladder and intestinal walls.

Cholangiofibrosis

Also called cholangiohepatitis, the cause of this pathology is thought to be from a Helicobacter species called H. cholecysticus. Affected hamsters display no clinical signs.
Macroscopic pathology includes bile duct hyperplasia, pericholangial fibrosis and centrilobular pancreatitis.

Lymphocytic Choriomeningitis Virus (LCM)

LCM is an RNA virus from the arenavirus group and is rare in hamsters, although most reported human cases have been associated with infected hamsters. In utero or perinatal infections may facilitate chronic infection resulting in a progressive wasting disease affecting the liver, spleen, lung, meningies and brain. Approximately 50% of hamsters will clear the infection.
A common route of infection of LCM in research laboratories is via the transplantation of LCM-containing tumours. Macroscopic pathology may include splenomegally, swollen or shrunken pitted kidneys and hepatomegally. Microscopic pathology may include lymphocytic meningitis, chronic glomerulonephropathy, widespread vasculitis and widespread lymphocytic infiltration.

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