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Gerbils (Laboratory) - Pathology (view source)
Revision as of 10:42, 18 August 2011
, 10:42, 18 August 2011→Tapeworm
==Introduction==
==Introduction==
Gerbils are part of the sub-family ''Gerbillinae'' which is part of the ''Rodentia'' order. There are approximately 100 species of gerbil in 14 genera from all over the world but in laboratory testing, as well as for keeping as a pet, the mongolian gerbil is the most common. The mongolian gerbil or 'jird', ''Meriones unguichulatus'' is commonly used for these purposes as they are known for having several characteristics that make them desirable over other species of gerbil. These inclue a very non-aggressive nature, a lower incidence than other species of spontaneous disease, a lack of odour and a monogamous mating behaviour. Some other species have been used for testing, although this is not common. The mongolian gerbil was introduced as a laboratory testing animal in 1963, although they only make up 0.5% of the total number of laboratory rodents used annually.
Gerbils are part of the sub-family ''Gerbillinae'' which is part of the ''Rodentia'' order. There are approximately 100 species of gerbil in 14 genera from all over the world but in laboratory testing, as well as for keeping as a pet, the mongolian gerbil is the most common. The mongolian gerbil or 'jird', ''Meriones unguichulatus'', is commonly used for these purposes as they are known for having several characteristics that make them desirable over other species of gerbil. These include a very non-aggressive nature, a lower incidence than other species of spontaneous disease, a lack of odour and a monogamous mating behaviour. Some other species have been used for testing, although this is not common. The mongolian gerbil was introduced as a laboratory testing animal in 1963, although they only make up 0.5% of the total number of laboratory rodents used annually.
==Strains and Stocks==
==Strains and Stocks==
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Some laboratory studies have found that under laboratory housing conditions, gerbils may develop a stereotypic digging behaviour. An example of this would be digging at the corner of the plastic housing container despite there being no material to move from the plastic. Changes in the housing parameters such as vastly increasing the housing size or the provision of natural substrates such as sand or soil has been shown to prevent this stereotypic digging behaviour. This behaviour often develops in juveniles. It has been shown that the provision of housing with burrows or a tiered tunnel structure can help to reduce this behaviour.
Some studies have found that under laboratory housing conditions, gerbils may develop a stereotypic digging behaviour. An example of this would be digging at the corner of the plastic housing container despite there being no material to move from the plastic. Changes in the housing parameters such as increasing the housing size or the provision of natural substrates such as sand or soil has been shown to prevent this behaviour. This behaviour often develops in juveniles. It has been shown that the provision of housing with burrows or a tiered tunnel structure can also help to reduce this behaviour.
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Gerbils are a social species and in the wild group sizes range from 2 to 15. There is usually only one actively reproductive male and female per group. The formation of new groups can be problematic when introducing adults to one-another due to issues of dominance and it is much better tolerated when introducing new juveniles to one-another. Adults will display strong xenophobic reactions towards unfamiliar animals including grinding their teeth and lashing their tails.
Gerbils are a social species and in the wild group sizes range from 2 to 15. There is usually only one actively reproductive male and female per group. The formation of new groups can be problematic when introducing adults to one-another due to issues of dominance and other animals are much better tolerated when introducing new juveniles to one-another. Adults will display strong xenophobic reactions towards unfamiliar animals including grinding their teeth and lashing their tails.
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Macroscopic findings will include numerous pruritic skin lesions.
Macroscopic findings will include numerous pruritic skin lesions. There may also be mild acanthosis, hyperkeratosis and accumulations of large numbers of neutrophils and macrophages in the adjacent dermis. Some gerbils may have concurrent hyperplasia of the Harderian gland.
===Staphylococcal Dermatitis===
This is an endemic disease that usually occurs in weanling gerbils. The gerbil will develop a localised alopecia and erythemia around the external nares which then rapidly spreads to the feet result in in moist dermatitis of the feet, legs and ventral body. Morbidity is between 75-100% and mortality is 25%. High humidity, fighting and stress associated with blood samples have all been shown to be causative factors.
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Macroscopic pathologic findings will include lesions that are acute and suppurative. Some gerbils may have micro-abcesses in the liver. Microscopic findings will vary depending on the severity of the lesions but will include minimal neutrophilic infiltrates in the epidermis with acanthosis and hyperkeratosis to severe suppurative epidermitis, dermatitis and folliculitis. In very severe lesions there may be chronic ulcerative dermatitis.
===Parasites===
===Parasites===
Parasites rarely cause disease in gerbils. The most common skin parasite is the hamster demodectic mange mites, ''Demodex aurati'' or ''Demodex criceti''. Usual clinical signs are alopecia.
Parasites rarely cause disease in gerbils. The most common skin parasite is the hamster demodectic mange mites, ''Demodex aurati'' or ''Demodex criceti''. Usual clinical signs are alopecia.
==Reproductive System==
==Reproductive System==
===Cystic Ovaries===
Geriatric problems in gerbils commonly include cystic ovaries. Cystic ovaries occur in 50% of geriatric females and can result in decreased fertility.
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Macroscopic pathologic findings will include moderate to large cysts on the surface of the ovaries together with metritis, endometrial hyperplasia and myometrial mineralisation.
==Urinary System==
==Urinary System==
===Lead Toxicity===
===Lead Toxicity===
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Macroscopic lesions may include a shrunken liver which will be darkly pigmented. The kidneys will also be small and pitted. Microscopic findings may include acid-fast inclusions within the proximal collecting ducts, tubules and within hepatocytes.
Macroscopic lesions may include a shrunken liver which will be darkly pigmented. The kidneys will also be small and pitted. Microscopic findings may include acid-fast inclusions within the proximal collecting ducts, tubules and within hepatocytes.
===Glomerulonephritis===
==Respiratory System==
Glomerulonephritis develops with concurrent polyuria and polydipsia together with progressive weight loss.
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Macroscopic pathology will show neoplastic lesions within the kidneys which will be shrunken, fibrotic and pitted.
==Nervous System==
===Aural Cholesteatomas===
Spontaneous aural cholesteatomas occur in 50% of gerbils over the age of two. The tumor displaces the tympanum of the ear into the middle ear. Clinical signs include a head tilt.
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Macroscopic pathologic findings will include compression within the inner and middle ear. There is often secondary infection in the ear which results in some bone necrosis and inner ear destruction.
==Cardiovascular System==
==Cardiovascular System==
Flagellated protozoa such as ''Giardia'' and ''Tritrichomonas'' are commonly found colonising the intestines of the gerbil. However, these protozoa are commensals and naturally occurring and therefore are usually not associated with any clinical signs. Overgrowth of these protozoa can lead to disease. Identification of these protozoa can be performed by faecal examination for cysts.
Flagellated protozoa such as ''Giardia'' and ''Tritrichomonas'' are commonly found colonising the intestines of the gerbil. However, these protozoa are commensals and naturally occurring and therefore are usually not associated with any clinical signs. Overgrowth of these protozoa can lead to disease. Identification of these protozoa can be performed by faecal examination for cysts.
====Tapeworm====
====Tapeworm====
The tapeworms ''Rodentolepis nana'' (dwarf tapeworm) or ''Hymenolepis diminuta'' can cause dehydration and diarrhoea. ''R. nana has a direct life cycle and has the potential to infect humans if ingested.
The tapeworms ''Rodentolepis nana'' (dwarf tapeworm) or ''Hymenolepis diminuta'' can cause dehydration and diarrhoea. ''R. nana'' has a direct life cycle and has the potential to infect humans if ingested.
===Enteritis===
===Enteritis===
====Salmonellosis====
The bacteria ''Salmonella enterica'' has been shown to cause enteritis in gerbils along with food deprivation. Clinical signs include moderate to severe diarrhoea, a rough coat, weight loss, depression and dehydration. Morbidity and mortality are higher in younger animals. Transmission is associated with food or bedding contaminated by insects and/or other gerbils.
The bacteria ''Salmonella enterica'' has been shown to cause enteritis in gerbils along with food deprivation. Clinical signs include moderate to severe diarrhoea, a rough coat, weight loss, depression and dehydration. Morbidity and mortality are higher in younger animals. Transmission is associated with food or bedding contaminated by insects and/or other gerbils.
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Macroscopic pathological findings will include a congested liver and distension within the gastrointestinal tract. There may also be a fibrinosuppurative peritonitis. The spleen may contain patchy pulmonary haemorrhage. There may also be a concurrent peritonitis. Microscopic findings will include a positive culture of ''Salmonella'' species.
Macroscopic pathological findings will include a congested liver and distension within the gastrointestinal tract. The liver may display multifocal necrogranulomatous hepatitis. Some of the larger hepatic granulomas may display mineralisation of the necrotic centres. There may also be a fibrinosuppurative or fibrinopurulent peritonitis. The spleen may contain patchy pulmonary haemorrhage. Microscopic findings will include a positive culture of ''Salmonella'' species.
====Listeriosis====
Listeriosis in gerbils is characterised by acute death without clinical signs.
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Macroscopic lesions include necrosuppurative hepatitis, enterocolitis, splenitis and hepatic and mesenteric lymphadenitis. There may also be diffuse acute pneumonitis.
===Starvation/Water Deprivation===
===Starvation/Water Deprivation===
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Macroscopic pathology will include multiple white foci of necrosis within the liver with associated mild to moderate enteritis. There may also be serosal oedema together with hyperaemia of the intestines. The intestines may also contain foamy, yellow faecal contents. There is also a potential for brain and cardiac involvement. A resultant septicaemia may lead to myocardial lesions and encephalitis. Microscopic pathology will include coagulative liver necrosis with only minimal inflammatory cell infiltrate. Definitive diagnosis is by demonstration of the organism within hepatocytes surrounding necrotic foci of the liver.
Macroscopic pathology will include multiple white foci of necrosis within the liver with associated mild to moderate enteritis. There may also be serosal oedema together with hyperaemia of the intestines. Intestinal lesions will be most pronounced in the distal ileum and cecum but can also occur in the duodenum, jejunum and colon. The intestines may also contain foamy, yellow faecal contents. There is also a potential for brain and cardiac involvement. A resultant septicaemia may lead to myocardial lesions and encephalitis. Microscopic pathology will include coagulative liver necrosis with only minimal inflammatory cell infiltrate. Definitive diagnosis is by demonstration of the organism within hepatocytes surrounding necrotic foci of the liver.
==Other==
==Other==
===Neoplasia===
===Neoplasia===
Older gerbils often develop spontaneous neoplasms. These most commonly affect the skin, adrenal glands, kidneys, spleen, intestine and the female reproductive tract. The most commonly encounteredt type of neoplasms include leiomyomas, subcutaneous fibrosarcomas, sebaceous gland adenomas, adenocarcinomas, duodenal adenocarcinomas, adrenal adenomas and malignant melanomas.
Older gerbils often develop spontaneous neoplasms. These most commonly affect the skin, adrenal glands, kidneys, spleen, intestine and the female reproductive tract. The most commonly encounteredt type of neoplasms include leiomyomas, subcutaneous fibrosarcomas, sebaceous gland adenomas, adenocarcinomas, duodenal adenocarcinomas, adrenal adenomas and malignant melanomas.
[[Category:Laboratory Animal Pathology]]
[[Category:Laboratory Animal Pathology]]