Chinchillas (Laboratory) - Pathology

Introduction

The chinchilla is a type of hystricomorph rodent and 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 of up to 20 years and can also be trained in basic techniques to facilitate easier laboratory techniques. Further to this viral and bacterial infections are relatively uncommon as are tumours.

Physiology

Most laboratory chinchilla are provided with a variety of components in their diet which includes pellets and hay. 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 very small volumes of urine with very little odour. The chinchilla requires room temperature (18-24C) and approximately 14hrs of daylight or artificial light if in labs, is optimal.

Within a laboratory environment chinchillas are not prolific breeders and they 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 commonly encountered rejection issues. Chinchillas have a post-partum oestrous ans 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 their grooming processes called dusting.

Diseases

Chinchillas that are suffering a 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.

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.