Today's Veterinary Practice

MAR-APR 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 74 FOCUS ON DIAGNOSIS Diagnosing distemper can be challenging and is based on history, clinical signs, and results of diagnostic tests. Abnormal hematologic findings consist of lymphopenia, thrombocytopenia, and regenerative anemia. In the early phase, distemper inclusions can be found in small numbers in circulating lymphocytes. Diagnostic imaging of the thorax shows an interstitial lung pattern in the initial phase. An alveolar lung pattern has been described with secondary bacterial infection. Immunocytochemistry (fluorescent antibody testing) can be performed, and submitted samples should contain cells from the conjunctival, tonsillar, genital, and respiratory epithelia. This special stain can also be used on cells in cerebrospinal fluid, blood (buffy coat), urine sediment, and bone marrow. In the clinical setting, smears from the epithelial lining of various tissues can be examined for inclusions by using a microscope in the clinic as a quick screening test. Cerebrospinal fluid taps should be performed in patients with neurologic signs. Cytological changes depend on the stage of infection, and a false-negative result can always occur in the early stages of the disease. Immunohistochemistry of tissue biopsies of the upper respiratory tract and the associated lymphatic system, as well as skin biopsies are diagnostic. Serum antibody titers can be evaluated by using a neutralization test. This is worth checking especially before an unapproved vaccine (in situations where no approved vaccine is available) is used in an animal that received multiple vaccines in the past. Postmortem findings show classic acidophilic inclusion bodies in the cytoplasm of epithelial cells of the mucous membranes, reticulum cells, leukocytes, glia, and neurons. 6 PREVENTION AND TREATMENT Supportive care with IV fluids (6ml/kg lactated Ringers solution IV) and antibiotics for secondary bacterial infections can be provided after culture and sensitivity testing. As the reported morality in ferrets is 100% 1-5 humane euthanasia is recommended in diagnosed patients with severe clinical signs. 12 Patients with a suspected infection should be quarantined and other unvaccinated exposed carnivores must be tested. Preventive vaccination is the most successful treatment of the disease. 1 Currently, only Purevax Ferret Distemper Vaccine (Merial) is available for vaccination in ferrets in the United States. It is a lyophilized vaccine of a recombinant canarypox vector expressing HA and F glycoproteins of canine distemper virus. Merial recommends to give two subcutaneous injections of 1mL (1 dose) at 3 week intervals and revaccinate annually with a single 1mL dose. Vaccination Because of inadequate circulating maternal antibodies, young ferrets aged 6 to 12 weeks become susceptible to CDV. 1 Purevax Ferret Distemper Vaccine (Merial) is approved for use in healthy ferrets starting at age 8 weeks. Vaccination should begin at age 6 to 8 weeks for kits, with booster vaccination provided every 3 to 4 weeks until age 14 weeks. Annual revaccination is recommended. A successful response to vaccination depends on the patient's immune system. Measuring antibody titers before the annual booster vaccination can be performed is considered the gold standard, 15 especially in ferrets with a history of vaccination reactions. A titer higher than 1:50 is currently considered high enough to provide immunity to CDV infection in ferrets. 16 A study by Jensen showed that cell- mediated immunity and/or the capacity for rapidly regenerating humoral immunity must be factored in; these can protect the patient from infection even if serum antibody levels are below the threshold. 5 FIGURE 4. An early sign of an anaphylactic vaccine reaction in the ferret. Note the significant piloerection of hair on the body and the tail. Supportive care should be administered immediately.

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