Hamsters (Laboratory) - Pathology

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Physiology

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

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;

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.

Digestive System

Cytomegalovirus (Salivary Gland Virus)

CMV often causes subclinical infections and associated immunosupression. CMV is transmitted via the placenta.
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.

Infectious Causes of Diarrhoea

Salmonella
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.
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.
There are often no findings in animals with acute infections.
Diagnosis is via isolation and culture of the Salmonella spp via faecal samples.
Chronic cases and those that recover from a Salmonella infection are likely to become carriers and should be destroyed to prevent further outbreaks.
Yersinia (pseudotuberculosis)
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.
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.
Clostridia
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.
Pathologic examination will show necrotizing ileitis and typhlitis. Hepatic lesions may be present and will be characterized by focal coagulative necrosis in periportal regions.
Antibiotic-Induced Enterotoxemia
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.
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.

Parasitic Causes of Diarrhoea

Nematodes
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.
Protozoa
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.
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.
Cryptosporidium species that colonise the intestine will cause weight loss and diarrhoea.
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.
Ascaridae
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.

Musculoskeletal System

Pododermatitis

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.

Osteoporosis

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.
The diet should contain a maximum of 1600iu of vitamin D per kg.

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.
Macroscopic pathology will show mineralisation/calcification of the heart, blood vessels, stomach, colon, kidneys and lungs.
The diet should have a calcium:phosphorus ratio of 1:5 and the same vitamin D level as above.

Scurvy

This condition is due to a deficiency of vitamin C where an adult guinea pig requires 10-30mg per day.
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.

Osteoarthritis

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.

Osteosarcoma

Although relatively uncommon in guinea pigs they can be seen as painful bony swellings in guinea pigs over 1 ear of age.

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.

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.

Middle Ear Disease

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.

Cleft Palate

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.

Cervical Lymphadenitis

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.
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.
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.

Wry Neck

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.

Epilepsy

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.
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.

Cerebellar Disease

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.

Heatstroke

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.