Raccoons are susceptible to a large number of different infectious agents including bacteria, viruses, and parasites. Several of these infectious diseases are zoonotic. Veterinarians are faced with the diagnosis and treatment of wildlife including raccoons and need to be able to make the correct diagnosis as well as educate clients on the potential hazards associated with exposure to raccoons.
Leptospirosis is a common bacterial disease in raccoons caused by a number of different species of Leptospira. Transmission is thought to occur via urine contamination of feed and water. Antemortem diagnosis is based upon serology and dark field examination of urine. Histopathologic examination and fluorescent antibody testing of liver and kidney are two postmortem procedures that can be done to help further aid the diagnosis of leptospirosis. Other natural bacterial infections reported in raccoons are listeriosis,yersiniosis,pasteurellosis, and tularemia.
Viral diseases of raccoons include rabies, canine distemper, raccoon parvoviralenteritis, infectious canine hepatitis, and pseudorabies. Rabies is a zoonotic disease that is endemic in raccoon populations in Pennsylvania and New England. In recent years, there has been a shift of rabies infected raccoons westward into Ohio (see Diagnostic Forum Vol. 8, No 2, 1997).
Canine distemper virus infection is probably the most common viral disease in raccoons. The clinical signs, and gross and histopathologic lesions in raccoons are similar to distemper in dogs. Neurologic signs due to distemper virus infection in raccoons are virtually indistinguishable from rabies induced neurologic disease. Diagnosis is based upon histopathologic lesions in brain, lung, spleen, and small intestine. Intranuclear and intracytoplasmicinclusion bodies can be visualized in many cells including epithelial cells in the respiratory epithelium, gastric mucosa, and transitional epithelium lining the renal pelvis and urinary bladder. The best tissues for fluorescent antibody testing and virus isolation of canine distemper virus are lung, brain, stomach, small intestine, kidney, and urinary bladder.
Parvoviral enteritis in raccoons is due to a unique raccoon parvovirus that is most antigenically similar to feline parvovirus. Clinical signs include bloody diarrhea, lethargy, inappetance, and loss of fear of humans. Raccoons do not develop clinical disease when exposed to canine parvovirus. Diagnosis is based upon histopathologic lesions of necrotizing enteritis and identification of the virus by fluorescent antibody testing. The most common method in which raccoons acquire pseudorabies virus infection is via the ingestion of virus-infected pig carcasses.
An important parasitic disease of raccoons is toxoplasmosis, which is a protozoal disease caused by Toxoplasmagondii.Felids are the definitive host for T. gondii, and they excrete potentially infective oocysts in their feces. Toxoplasmosis in raccoons is commonly associated with immunosuppression from canine distemper virus infection. Necrotizing encephalitis and pneumonitis are frequent lesions associated with toxoplasmosis.
Another parasite of importance in raccoons is Baylisascarisprocyonis, which is an intestinal roundworm of raccoons. Baylisascaris is a known cause of cerebral nematodiasis and ocular and visceral larval migrans in domestic and non-domestic animals, and humans. Transmission commonly occurs through the ingestion of infective eggs, which results in aberrant migration in hosts other than raccoons.