RESPIRATORY disease is a common problem in exotic species in general practice, whether avian, reptilian or small mammal.

Different species have different disease susceptibilities. These vary according to:

The complicated sinus system of birds coupled with a tendency to form solid pus means that upper respiratory disease (URD) and sinusitis are common problems in many avian species. Reptiles lack a muco-ciliary escalator meaning they find it hard to remove respiratory discharges. This is one factor contributing to lower respiratory disease (LRD) in snakes. Rabbits suffer from compression of lungs and upper respiratory passages. Breeding to produce extremes of shape (especially "squashed nose" breeds) is a major factor in both upper and lower respiratory disease.

There are few primary pathogens found in respiratory syndromes. Snake paramyxovirus may be an exception as may Bordetella bronciseptica in guinea-pigs. Other infectious agents may appear to act as pathogens in stressed or immunologically naïve animals, eg Pasteurella in rabbits or chelonid herpesvirus in tortoises. Mixing of species in households may, therefore, hold dangers, eg mixing tortoise species will allow exchange of herpesviruses and Mycoplasma spp between these species. While one tortoise may cope with its own adapted organisms, another may not. Mixing of rabbits and guinea-pigs allows rabbits (who will often carry Bordetella as part of the normal respiratory flora) to pass these organisms to guinea-pigs that don't. The susceptibility of different species to different organisms is amply illustrated by the incidence of aspergillosis in different bird species. Aspergillus spp spores are found in the environment and disease represents either lowered immunity to the organism or overwhelming infection. Grey parrots, Gyr falcons and Goshawks are some of the species that appear very susceptible and disease is commonly seen in them. Peregrines and cockatoos are much more resistant so disease is rarely seen in these species.

When we think of husbandry-related disease we often think of reptile problems and this  is  often the case in respiratory disease. These problems (especially URD in tortoises and LRD in snakes) are often the results of low temperatures. Inappropriate humidity levels will contribute to respiratory disease in a range of species, both  reptilian  and  avian. Exposure to irritants, especially cigarette smoke, air fresheners, cooking  fumes,  etc will often cause direct  irritant  effects or predispose to infection especially aspergillosis in birds. Some may  be  linked  to  the  development  of allergy and/or asthma although this diagnosis remains controversial  in  exotic animal  medicine. Other irritants may include dusty bedding  in  rabbit or rodent hutches/ cages. Rotting organic matter in bird  aviaries  provides  a  direct   source of   Aspergillus   stores.   Sudden    changes    in

JOHN CHITTY BVetMed, CertZooMed, MRCVS

husbandry, eg rapid temperature changes or mixing of individuals, will cause stress and therefore, affect immunity. Underlying systemic infection may also play a part - the young Grey parrot with an airsac aspergilloma may seem a clear diagnosis. However, if on haematology there are few if any white blood cells then be aware that it may be suffering from immunosuppression caused by circovirus infection.

Hypovitaminosis A is a well-known cause of respiratory disease in birds. Lack of this vitamin results in keratinisation of glands in the mucous membranes with subsequent abscessation and infection. Quality of overall diet should also be considered. Many seed diets for parrots are of extremely poor quality and often stored badly as well. Opening seed hulls will often reveal fungal growth within - a common source of Aspergillus spores. As a physical effect, inhaled seeds may be a cause of tracheal blockage in parrots. In rabbits there is a very thin layer of bone between tooth roots and nasal cavity - many cases of URTD result from tooth root abscesses. (Fig. 1)

Figure 1. Cross-section through a rabbit maxilla at the level of the molars. Note the thin section of bone separating teeth from nasal cavity. It is easy to see how easily dental infection will penetrate the nasal cavity.

A range of causes cause a range of diseases, often with similar symptoms. Accurate diagnosis is, therefore, essential and often complicated - after all, the best therapeutic agents in the world cannot work if used for the wrong condition! It is also vital to explore the many underlying causes. As stated earlier, there are few primary pathogens and, while your diagnosis of a bacterial pneumonia in a boa constrictor may be correct and you may be using an appropriate antibacterial, there is no chance of success unless the snake is provided accommodation with appropriate temperature ranges, appropriate humidity ranges, and the ability to climb (arboreal snakes often require this so gravity can assist in the clearance of respiratory discharges). The most common question asked in exotics practice is not so much "what  has  it  got?",  but "why  has  it  got  it?"

The following are often required as part of a comprehensive respiratory investigation:

This often provides many of  the clues  as  to "why". Full  details  of   husbandry  and  diet  are  required.

Some cases are easy to pick as respiratory problems there may be abscesses in the nasal area or an obvious oculo-nasal discharge (Fig 2). Alternatively dyspnoea or cyanosis may be easily identified. However, it must be remembered that many of these