Serological surveillance of plague in dogs and cats, California, 1979-1991

Following natural infection both cats and dogs develop antibodies to plague which can be measured for several months after infection. Besides being helpful in the diagnosis of plague in domestic carnivores, the antibody titer has important implications in outbreak investigation and surveillance programs. We report the first serological survey for plague in domestic carnivores conducted in California between 1979 and 1991 in five different settings or programs. A total of 4115 dogs and 466 cats were tested for plague antibody by the passive hemagglutination test. 86 dogs (2.09%) and 15 cats (3.22%) had plague antibody titers > or = 1:16. The percentage of positive dogs and cats were respectively 3.96% and 0% on reservations, 3.27% and 1.39% on military bases, 0.74% and 1.25% in Los Angeles County and 0% and 4.61% in veterinary clinics, but 41.38% and 41.2% from outbreak investigations. Titers ranged from 1:16 to 1:4096 in dogs and cats, but were low in dogs and cats in the Los Angeles County survey and on the military bases. Serologic testing of pets during human case investigation or increased rodent mortality should be regularly implemented, as well as dog surveys on reservations. Surveys of pet dogs in veterinary clinics did not appear worthwhile, even if selected from plague endemic regions. Veterinarians should report suspect cases in cats to public health authorities, that will improve plague surveillance and reduce the risk of humans contracting the disease from their pets.