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The pathogenesis of South American and North American myxoma viruses was examined in two species of North American lagomorphs, Sylvilagus nuttallii (mountain cottontail) and Sylvilagus audubonii (desert cottontail) both of which have been shown to have the potential to transmit the South American type of myxoma virus. Following infection with the South American strain (Lausanne, Lu), S. nuttallii developed both a local lesion and secondary lesions on the skin. They did not develop the classical myxomatosis seen in European rabbits (Oryctolagus cuniculus). The infection at the inoculation site did not resolve during the 20-day time course of the trial and contained transmissible virus titres at all times. In contrast, S. audubonii infected with Lu had very few signs of disseminated infection and partially controlled virus replication at the inoculation site. The prototype Californian strain of myxoma virus (MSW) was able to replicate at the inoculation site of both species but did not induce clinical signs of a disseminated infection. In S. audubonii, there was a rapid response to MSW characterised by a massive T lymphocyte infiltration of the inoculation site by day 5. MSW did not reach transmissible titres at the inoculation site in either species. This might explain why the Californian myxoma virus has not expanded its host-range in North America.

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Between August 1993 and September 1994 we documented serological responses of coyotes (Canis latrans) vaccinated with two commercial rabies vaccines licensed for use in domestic dogs. Serologic responses were documented by testing for rabies virus neutralizing antibodies with the rapid fluorescent focus inhibition test (RFFIT) at 30, 90, 180, 270, and 365 days post-vaccination. All coyotes vaccinated with Imrab 3 (Rhone-Merieux, Inc.), and 75% of those vaccinated with Dura-Rab 3 (Immunovet, Inc.) seroconverted, as evidenced by the presence of antirabies antibody titers > or = 1:5 in one or more of the five post-vaccination samples. The percent of coyotes showing a titer > or = 1:5 was generally greater and titer levels appeared higher and more persistent among animals vaccinated with Imrab 3 than Dura-Rab 3. Presence of titers via RFFIT tests demonstrates the antibodies produced in coyotes by these rabies vaccines functionally bind and neutralize rabies virus in vitro, but these results do not constitute a demonstration of protection required for licensure for use in coyotes.

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One of seven female coyotes (Canis latrans) captured in Webb County, Texas during September 1986 and confined and mated in holding facilities at Millville, Utah whelped the following spring. The maternal female (greater than 5-yr-old) and her five neonates were killed at 22 days postparturition. All were infected with adult Ancylostoma caninum and were passing eggs in their feces. Also, the neonates and maternal female were infected with immature and adult Alaria marcianae, respectively. These findings suggested that the transmammary route is an important transmission mechanism for acquisition of these species of helminths in coyotes. The lack of overdispersion in the frequency distribution of these parasites and infection of the entire litter indicated that transmission from the infected female was nonselective among the pups.

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Serum samples from 228 coyotes were selected randomly from a serum bank assembled from Texas from 1975 to 1984 and were evaluated serologically for neutralizing antibodies against canine distemper virus (CDV). One hundred and twenty-eight (56%) of the 228 coyotes had antibody titers of greater than or equal to 1:5 against CDV (seropositive). The serologic prevalence (seroprevalence) of antibodies against CDV infection was higher in the spring (62%) than in the fall (40%). The seroprevalence of CDV in various age groups was different; 25 of 101 coyotes (25%) were seropositive at less than 1 year of age, 35 of 52 (67%) were positive between 1 and 2 years of age, and 68 of 75 (91%) were positive at greater than or equal to 2 years of age. The results indicated that CDV was enzootic in coyote populations of southern Texas, with an increasing number of seropositive coyotes noted annually. The sex of the coyote did not appear to be related to the seroprevalence against CDV.

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The prevalence of serum antibodies against canine parvovirus-2 (CPV-2), as measured by a standard hemagglutination-inhibition test, was determined in serum samples collected from 1,184 coyotes (Canis latrans) in Texas, Utah, and Idaho from 1972 to 1983. No evidence of parvoviral infection was found before 1979, after which seroprevalence rapidly increased to greater than 70% at all sites by 1982. There were minor differences in prevalence between age groups and among sites, but no consistent differences between sexes. The onset of CPV-2 seroprevalence in free-ranging coyotes coincided remarkably with the recognition of the clinical disease and seroprevalence in domestic dogs in the United States.

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