Closantel is a flukicide agent routinely used on farms and in veterinary practice. Closantel is available in oral, topical and injectable forms, often mixed with other anthelmintics. Rafoxanide is a closely related product and is only in oral form. Closantel toxicity has been reported in sheep, cattle, goats and rarely humans (Oliveira et al. 2022; O Leary et al. 2023); the authors have seen cases in farmed deer. The product damages the white matter of the cerebrum, cerebellum and spinal cord, causing ataxia and immense distress in deer. This has been known to result in trauma, dislocations and fractures in affected animals.

The most frequent signs following closantel intoxication include loss of appetite, ataxia or uncoordinated movements, weakness, visual disturbances and blindness. After oral administration, closantel is readily absorbed into the bloodstream, where >99% of the unchanged closantel binds strongly to plasma proteins. Peak plasma levels are reached within 48 hours of administration, regardless of the route of administration. Closantel is poorly metabolised and excreted in the faeces through the bile.

The central nervous system, retina and optic nerve are commonly affected. Histopathological changes are spongiosis in the brain white matter and spinal cord. Changes in the optic nerve following closantel overdose include spongiform change, oedema and myelin vacuolisation, resulting in atrophy of the optic disc. The portion of the optic nerve passing through the bone becomes compressed, resulting in damage to the myelin sheath.

Confirmation of toxicity is based on clinical signs and a history of recent closantel administration in affected deer. Histopathology of the brain or spinal cord could be used to confirm the diagnosis.

The effects of closantel intoxication are often permanent and irreversible with no specific antidote for closantel. Treatment consists of supportive measures, while euthanasia is the only option for most affected animals. Deer appear to be more severely affected by toxicity than sheep; this is in partly due to their highly strung nature and stress response, although the absence of a gall bladder may influence the rate of excretion.

Necrobacillosis is caused by Fusobacterium necrophorum, which has been prevalent in farmed species since the 1800s. Necrobacillosis has been reported in numerous deer species, including mule deer (Odocoileus hemionus), white-tailed deer (Odocoileus virginianus), elk (Cervus elaphus wapiti), caribou (Rangifer tarandus caribou), red deer (Cervus elaphus), sambar (Cervus unicolor) and semi-domesticated tundra reindeer (Rangifer tarandus tarandus; Handeland et al. 2010).

Fusobacteriosis in deer is not common, although when outbreaks occur, it can become widespread in the group causing significant disease and deaths. Cuts to the feet or lower legs can lead to infected limbs, especially in cold muddy conditions. Some form of breakdown of the skin barrier or hoof barrier is required for entry of bacteria to cause infection. This can be erosion and wearing off of the toe due to scuffing on rough or uneven concrete, allowing infection to track up the point of the toe. Similarly, separation of the hoof wall from the sole and hoof structure is due to lateral pressure on the hoof, potentially from fighting or pressuring animals during handling. Feet constantly wet or heavily contaminated with dirt or faecal material are at greater risk. Penetrating wounds from sharp stones, stalky pastures, thistles and foreign objects such as wire or nails can result in damage to the skin. The problem is exacerbated by stress brought on by events like cold weather, mixing groups or housing.

While Fusobacterium survive well in soil and mud, it is likely that the primary reservoir for F. necrophorum is animals that are shedding the bacterium in the faeces or on diseased feet. Strains of F. necrophorum are normally found within the alimentary tract, especially within the rumen, and are then shed into the environment. Pathogenic strains are thought to be part of this microbiota.

Initially, deer present with thickened skin with erythema and alopecia or, more severely, with infected swollen joints, ligaments and tendons. Foot abscess will develop above the claw area, which can penetrate the joint cavity; this initially presents as lameness and ultimately the deer will become non-weight bearing. The necrotic appearance and smell of superficial lesions may be considered pathognomic.

Necrobacillosis can also be associated with lesions in the mouth and throat (necrotising stomatitis), umbilicus, liver and lungs of deer, it is rarely associated with abortion. The bacteria can establish in the spinal cord resulting in partial paralysis of one or both hind legs. Untreated infections can be fatal. In some cases, deaths are the first sign the disease is present on the farm. Death is often the result of spread of infection to the liver, lungs or kidneys. Even mildly affected deer will have reduced growth rates or weight loss and may be more likely to be bullied.

Diagnosis is straightforward, in the case of foot abscess the foot area above the claw will be swollen and discharge pus. Culture of the organism, sampling the edges of infected lesions, should be undertaken to confirm the cause. At postmortem examination, abscesses may be visible in many locations and culture should be straightforward; additional confirmatory techniques may include in situ hybridisation and PCR (Handeland et al. 2010).

Reducing the incidence of infection involves reducing stress around weaning, managing the environment to reduce the risk of foot injury, as well as rapid and appropriate use of antibiotic treatment (based on oxytetracyclines). Infections in their early stages can be cured with antibiotics; the treatment of advanced infections is usually futile. Wounds and lesions can be flushed and cleaned with multiple anti-bacterial agents, combined with the administration of antibiotics.

Careful consideration should be made before prophylactic treatment of the group is undertaken. The numbers affected and the risk of animals shedding bacteria must be balanced against the risks associated with handling and further stress on the group. It is relatively easy to identify lame deer when relaxed in their usual environment, but during handling, it will be very difficult to identify those affected.

Necrobacillosis has been particularly reported in pronghorn (Antilocapra americana), elk (Cervus canadensis), mule deer (Odocoileus hemionus) and white-tailed deer (Odocoileus virginianus

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