Chinchillas (Laboratory) - Pathology

Introduction

The chinchilla is a type of hystricomorph rodent of which there are two types; the Chinchilla langier, or long-tail and the Chinchilla chinchilla which has a short tail. Chinchilla are found in the wild at altitudes of between 9,000-12,000 ft within the Andes in South America. Chinchilla have been kept in captivity since 1923 when a small number of animals were brought to North America.

Chinchillas are used in laboratory experiments for a number of reasons but a common reason is that the chinchilla has a hearing range that is closest to that of humans. Therefore many experiments researching the auditory system utilise chinchillas. Research using chinchillas has been undertaken since the 1970s. Chinchillas also make good laboratory animals as they are relatively easy to maintain, have long life spans (up to 20 years) and can also be trained in basic techniques to facilitate easier laboratory handling. Further to this, viral and bacterial infections are relatively uncommon, as are tumours.

Physiology

Chinchilla should be provided with a variety of components in their diet including mainly hay and pellets. Although chinchillas eat large volumes of hay they do not drink a proportionate volume of water and chinchillas are known to survive on remarkably small amounts of water. Chinchillas have very dry faeces and only produce small volumes of urine with very little odour. The laboratory chinchilla requires room temperature (18-24C) and approximately 14hrs of daylight/artificial light to be optimal.

Within a laboratory environment chinchillas are not prolific breeders and there can be difficulty in maintaining breeding stocks. Puberty is not usually reached until approximately 8 months old and they have long oestrous cycles of 41 days, with 2 to 3 days of oestrous. The length of gestation for a chinchilla is 111 days and the range of litter sizes varies between 1 to 6 with 1 or 2 'kits' most common. Larger sized litters may result in fatal fighting amongst the kits.

Kits are usually weaned at between 6 to 8 weeks and at this age it is possible to pass these young onto another lactating mother without any rejection issues. Chinchillas have a post-partum oestrous and therefore it is possible to produce two litters in a breeding season which is between November to May, although the male is fertile throughout the year.

Copulation between chinchillas can be confirmed by the existance of a copulatory plug.

General Behavioural Characteristics

Unless regularly handled, adult chinchilla can be very aggressive. This is especially common in females and therefore these should be kept in separate cages. If weanlings or young chinchillas are introduced to another female it is likely that the adult will kill the young.

Most chinchilla require a sand-bathing tray for grooming or 'dusting'.

Diseases

Chinchillas suffering some form of disease will often exhibit clinical signs such as laboured breathing, poor quality hair coat, weight loss, hunched posture or an abnormal gait. Lethargy and/or unresponsiveness are also common findings in the sick animal. Therefore these clinical signs will often represent the precursor to more advanced disease or pathology.

Nervous System

Conjunctivitis

Conjunctivitis is rarely seen in adults but can be seen in young animals and is often the result of a foreign body. A common example of this is dust bath sand causing irritation to the eye. Clinical signs including purulent conjunctivitis may indicate a bacterial infection with Staphylococcus sp and Pseudomonas aeruginosa species being reported.

Gross pathology may show eyes that have visible oedema, a hyperaemic conjunctiva and either a serous or purulent ocular discharge.

Otitis Media

Otitis media is common in younger animals and is often a secondary infection to a respiratory infection or other trauma. Depending on the severity and location of the infection neurological clinical signs may be apparent which include ataxia, circling or rolling.

Macroscopic pathology may include considerable scar tissue that can result in blockage of the ear canal. Where this occurs cerumen and debris are often trapped inside. The tympanic membrane is often thickened. The ear canal and tympanic membrane will be acutely inflammed. This inflammation may progress to the inner ear and/or meninges.

Baylisascaris procyonis Infection

This nervous system disease is also referred to as 'Cerebral Nematodiasis'. B. procyonis is a roundworm commonly found in raccoons and transmission can occur following ingestion of feed contaminated by raccoon faeces. Chinchillas infected with the disease may exhibit a number of clinical signs including recumbancy, paralysis, ataxia, incoordination, head tilt, coma and death.

Gross lesions may include multifocal necrosis of the brain. Histopathology may include meningitis with sections containing ascarid larvae within the midbrain, medulla and cerebellum.

Protozoal Meningioencephalitis

Protozoal species including Toxoplasma gondii and Frenkelia sp. are associated with meningioencephalitis in chinchilla. Although rare, clinical signs of infection include a purulent nasal discharge, cyanosis, incoordination, depression, weight loss and dyspnea.

Macroscopic pathological findings may include haemorrhagic lungs and an enlarged spleen. The myocardium, brain, pancreas and intestines may also be grossly enlarged. Microscopic pathological findings may include Toxoplasma pseudocysts or bradyzoites within the tissue of the lungs, brain, myocardium, pancreas or intestines. Tachyzoites may also be found in blood and/or lymphatic fluids.

Herpesvirus 1 Infection

A spontaneous infection with human-type herpesvirus-1 has been reported in chinchillas and clinical signs include recumbancy, disorientation, seizures and progression to death.

Microscopic pathological findings may include non-supparative meningitis and/or polioencephalitis with associated neuronal necrosis. There may also be intranuclear inclusion bodies primarily affecting the brain stem and cerebral cortex. Ulcerative keratitis, uveitis, retinitis, retinal degeneration, optical neuritis and purulent rhinitis have also been associated with herpesvirus-1.

Cardiorespiratory System

Upper Respiratory Tract Infection

The causes of upper respiratory tract infection in chinchillas are thought to be wide ranging and include humidity, overcrowding and poor ventilation. Bacterial infections caused by Streptococcus sp., Pseudomonas sp., Bordetella sp. and Pasturella sp. are most common with these agents initially infecting the nasal sinuses and/or mucous membranes. Clinical signs may include nasal discharge, conjunctivitis and sneezing. Acute cases can result in sudden death.

Macroscopic pathological findings may include necrotic sinus cavities which can be filled with a mucopurulent debris. In more advanced cases the infection may track to the brain. Diagnosis is via isolation and culture of the causative agent.

Pneumonia

In chinchilla this is commonly cause by bacterial infection, usually by similar species to the upper respiratory tract infection above. A species of fungus Histoplasma capsulatum has also bee associated with hay and pneumonia in chinchilla. Pneumonia is thought to be caused by housing in damp, cold environments. Clinical signs may include laboured breathing, coughing/sneezing and a mucopurulent discharge. In chinchillas pneumonia may also be accompanied by conjunctivitis, weight loss and the other more general signs discussed at the beginning of the disease section. Sudden death due to sepsis may occur.

Macroscopic lesions may include pneumonic lesions in the lung parenchyma and bronchi and general inflammation.

Digestive System

Pseudomonas aeruginosa Infection

This is often a secondary infection due to stress and has been linked to drinking water and the general cage environment. Transmission is via aerosol, fecal-oral routes and via contact between animals. Clinical signs can include anorexia, depression, diarrhoea/constipation, mastitis, intradermal pustules and acute death. This infection is a multifocal systemic infection.

Macroscopic lesions can include abcesses throughout multiple organs, a generalised lymphadenopathy and generalised multifocal necrosis.

Listeria monocytogenes Infection

L. monocytogenes infections are associated with poor sanitation and contaminated feeds and/or water. Tranmission is via the fecal-oral route. Chinchillas appear to be particularly susceptible to this species of bacterium. Clinical signs are consistent with those found with P. aeruginosa infections (above). Additionally, this infection may also have a neurological element which may include flaccid ears, ataxia, circling and convulsions.

Macroscopic lesions may include fibrinous peritonitis, broad multifocal mamillary necrosis and widespread intersitial pneumonia. Most organs are susceptible to L. monocytogenes. Microscopic histopathology may include monocytic perivascular cuffing in brain tissues.

Yersina Infections

Two species of Yersina have been isolated from chinchillas; Y. pseudotuberculosis and Y. enterocolitica. Both are types of gram-negative bacteria. Transmission is both via fecal-oral routes but also transplacental and milkborne. Infection can be asymptomatic but there is a high morbidity and mortality rate associated with infection. Clinical signs are consistent with other forms of bacterial infection such as those above.

Gross pathology associated with Y. pseudotuberculosis will often include granulomatous lesions primarily in the liver spleen and lungs. Gross pathology associated with Y. enterocolitica will cause similar lesions in these organs but also within the lymph nodes, intestines and kidneys.

Iatrogenic (Antibiotics)

The administration of inappropriate antibiotics such as lincomycin, cephalosporins, penecillins or amoxicillins may result in a decrease in the usual gram-positive gut flora and an increase in gram-negative bacteria causing enterotoxaemia. Clostridium perfringens is the most common gram-negative causative agent of enterotoxaemia. Clinical signs will include emaciation, diarrhoea, lethargy, dehydration and if untreated, death.

Gross pathology will include enlarged liver and spleen. The lining of the gut may be inflammed in some cases.

Constipation

Constipation is more common than diarrhoea in chinchillas and is often due to insufficient dietary fibre and/or roughage. The causes of constipation have also been linked to dehydration, environmental stress, intestinal obstruction, obesity or uterine compression in pregnant females.

Gross pathology will include gut contents that consist of fecal pellets that will be thin, hard and in some cases stained with blood. In more chronic cases there may be rectal prolapse or intestinal torsion, colonic flexure or cecal impaction. Chronic cases may also display intestinal adhesions, foreign bodies or abcesses.

Gastric Ulcers

Gastric ulcers are common in young chinchilla and are most often caused by feed that is too course, fiberous or mouldy.

Macroscopic lesions may include gastric mucosal ulcers and/or erosions that may be covered with a thick dark fluid.

Other

Septicaemia

Septicaemia is most commonly a secondary infection to bacterial enteritis. Bacterial species such as Streptococcus and Pasturella have been linked to such multisystemic infections. Animals can progressively degenerate or can die suddenly depending on the severity of the infection.

Gross pathology findings may include septicemic organs and may be diffusely congested. The organs may also contain bacterial emboli.

Heat Stress

Chinchillas are highly temperature sensitive, especially to sudden changes in environmental temperatures. Clinical signs of heat stress will include restlessness, rapid respiration and hypersalivation.

Macroscopic lesions will include markedly congested lungs.