Roxarsone and arsanilic acid are used to promote growth and to treat swine dysentery and eperythrozoonosis. Roxarsone is more toxic than arsanilic acid but most features of poisoning are similar in both cases. Poisoning is dose-related. Chronic poisoning may occur when low doses are given over a long period of time. Acute poisoning occurs when large amounts are consumed in a short period of time.
Signs of chronic poisoning with arsanilic acid include goose-stepping, hind limb ataxia, limb paresis, and blindness. Blindness is not typical of poisoning with other organic arsenicals. Paralyzed pigs remain alert. If provided with feed and water, they will continue to eat and drink. There are few or no associated gross lesions. Signs of acute poisoning include cutaneous erythema, ataxia, vestibular disturbances, and terminal muscular weakness. An acute gastroenteritis will often be present in these cases. Although signs and lesions of roxarsone poisoning will often be similar, an additional syndrome has been described that includes repeated convulsive seizures following exercise without the blindness produced by arsanilic acid. Microscopic lesions associated with chronic poisoning by these compounds include neuronal degeneration of optic and peripheral nerve trunks, including the sciatic nerves. Neuronal lesions may not be present in acute cases.
A tentative diagnosis can often be based on a history of misuse of the compounds and the presence of characteristic clinical signs in chronically affected swine. Diagnosis may be assisted by toxicologic assays of kidney, liver, muscle, and feed.
Prevention of organic arsenical poisoning can be achieved simply by correct management of these legal compounds during feed preparation or medication. In particular, water treated with these compounds should not be given to thirsty pigs, as they are likely to consume a toxic dose. Directions provided with the compounds should be followed carefully. The neurotoxic effect of poisoning sometimes is reversible if the compound is removed within two or three days of the appearance of signs. Blindness and long standing peripheral nerve damage may be permanent.