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Marfin, A. A., Petersen, L. R., Eidson, M., Miller, J., Hadler, J., Farello, C., et al. (2001). Widespread West Nile virus activity, eastern United States, 2000. Emerg Infect Dis, 7(4), 730–735.
Abstract: In 1999, the U.S. West Nile (WN) virus epidemic was preceded by widespread reports of avian deaths. In 2000, ArboNET, a cooperative WN virus surveillance system, was implemented to monitor the sentinel epizootic that precedes human infection. This report summarizes 2000 surveillance data, documents widespread virus activity in 2000, and demonstrates the utility of monitoring virus activity in animals to identify human risk for infection.
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Barwick, R. S., Mohammed, H. O., McDonough, P. L., & White, M. E. (1998). Epidemiologic features of equine Leptospira interrogans of human significance. Prev Vet Med, 36(2), 153–165.
Abstract: Leptospirosis is a zoonotic bacterial disease caused by Leptospira interrogans. There is a serologic evidence that horses are exposed to L. interrogans and, as a shedder of these organisms, can be a threat to humans. We examined risk factors associated with the risk of testing seropositive to three L. interrogans serovars (L. icterohaemorrhagiae, L. grippotyphosa, and L. canicola) in the horses of New York State, in order to understand the epidemiology of the disease and suggest strategies to control and prevent equine leptospirosis. To carry out this study, blood samples were collected from a random sample of 2551 horses and tested for the presence of antibodies to the above serovars using the microscopic agglutination test. Samples with a titer $100 were considered positive. Clinical and demographic data were collected on each horse, the farms' management practices and ecology. Logistic regression analysis was used to develop a multivariate indexing system and to identify factors significantly associated with the risk of leptospirosis. Four indices were developed based on the possible sources of exposure: rodent exposure index; wildlife exposure index; soil and water index; and management index. The soil and water index was significantly associated with the risk of exposure to all three serovars. Management was positively associated with L. icterohaemorrhagiae and L. canicola. Density of horses turned out together was positively associated with the risk of exposure to L. grippotyphosa. We concluded that indirect exposure of horses to L. interrogans through contaminated soil and water appears to be significantly associated with the risk of exposure to all three serovars. Management appears to play an important role in the exposure to L. interrogans. Modification of management practices might reduce the horses' risk of exposure and hopefully minimize the human hazards.
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Kida, H. (1997). [Ecology of influenza viruses in animals and the mechanism of emergence of new pandemic strains]. Nippon Rinsho, 55(10), 2521–2526.
Abstract: Ecological studies on influenza viruses revealed that the hemagglutinin genes are introduced into new pandemic strains from viruses circulating in migratory ducks through domestic ducks and pigs in southern China. Experimental infection of pigs with 38 avian influenza virus strains with H1-H13 hemagglutinins showed that at least one strain of each HA subtype replicated in the upper respiratory tract of pigs. Co-infection of pigs with a swine virus and with an avian virus generated reassortant viruses. The results indicate that avian viruses of any subtype can contribute genes in the generation of reassortants. Virological surveillance revealed that influenza viruses in waterfowl reservoir are perpetuated year-by-year in the frozen lake water while ducks are absent.
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Fulhorst, C. F., Hardy, J. L., Eldridge, B. F., Chiles, R. E., & Reeves, W. C. (1996). Ecology of Jamestown Canyon virus (Bunyaviridae: California serogroup) in coastal California. Am J Trop Med Hyg, 55(2), 185–189.
Abstract: This paper reports the first isolation of Jamestown Canyon (JC) virus from coastal California and the results of tests for antibody to JC virus in mammals living in coastal California. The virus isolation was made from a pool of 50 Aedes dorsalis females collected as adults from Morro Bay, San Luis Obispo County, California. The virus isolate was identified by two-way plaque reduction-serum dilution neutralization tests done in Vero cell cultures. Sera from the mammals were tested for antibody to JC virus by a plaque-reduction serum dilution neutralization method. A high prevalence of JC virus-specific antibody was found in horses and cattle sampled from Morro Bay. This finding is additional evidence for the presence of a virus antigenically identical or closely related to JC virus in Morro Bay and indicates that the vectors of the virus in Morro Bay feed on large mammals. A high prevalence of virus-specific antibody was also found in horses sampled from Marin and San Diego counties. This finding suggests that viruses antigenically identical or closely related to JC virus are geographically widespread in coastal California.
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Atwill, E. R., Mohammed, H. O., & Lopez, J. W. (1996). Evaluation of travel and use as a risk factor for seropositivity to Ehrlichia risticii in horses of New York state. Am J Vet Res, 57(3), 272–277.
Abstract: OBJECTIVES--To determine whether mean annual frequency and destination of equine travel was associated with exposure to Ehrlichia risticii and whether these associations were modified by horses' place of residence. DESIGN--Cross-sectional study. SAMPLE POPULATION--511 equine operations containing 2,587 horses were visited in New York state from a target population of 39,000 operations. PROCEDURE--Each horse was tested for serum antibodies against E risticii, using indirect fluorescent antibody. Information on the horse's travel history, farm's management practices, and surrounding ecology was obtained by personal interview and resource maps. Statistical analyses were performed on 2 cohorts of animals: all horses enrolled in the study and horses born on the property or that resided at least 4 years on the farm. Three county-based risk regions (RR) were identified by use of cluster analysis. RESULTS--Mean seroprevalence for each of the 3 RR was 2.4 (low risk), 8.5 (moderate risk), and 18.5% (high risk) for cohort 1 and 2.5, 8.0, and 18.4% for cohort 2. Among cohorts 1 and 2, pleasure riding and breeding trips were associated with exposure to E risticii, but horse residence (low, moderate, or high RR) was an effect modifier for these associations. Among cohort 1 and stratifying the analysis according to the RR for the travel destination, trail riding at low RR and trail riding at high RR were associated with exposure. Among cohort 2 and stratifying the analysis according to the RR for the travel destination, breeding trips were associated with exposure, and strong effect modification was present for horse residence (low, moderate, or high RR). CONCLUSIONS--Only certain types of travel to specific RR were associated with higher risk of exposure to E risticii. In many instances, travel was not associated, or was associated, with a reduced risk of exposure.
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Gothe, R. (1994). [Tapeworms, a problem in equine practice?]. Tierarztl Prax, 22(5), 466–470.
Abstract: This paper gives a survey on biology and ecology of equine tapeworms as well as on pathogenesis, clinics, diagnosis, therapy, and prophylaxis of tapeworm infections.
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Forbes, A. B. (1993). A review of regional and temporal use of avermectins in cattle and horses worldwide. Vet Parasitol, 48(1-4), 19–28.
Abstract: Ivermectin and abamectin are two members of the group of parasiticides known as the avermectins; ivermectin was first registered as an injectable treatment for cattle in 1981. Since then, abamectin has been registered for cattle and ivermectin for horses. The relative popularity of the avermectins amongst farmers and veterinarians can be attributed to their spectrum of activity, convenience, wide margin of safety and the improved health and performance of stock following their use. Patterns of use in grazing animals apply equally to the avermectins as to other antiparasitics, particularly anthelmintics; these are based on a knowledge of epidemiology integrated with practical management considerations. For cattle, programs are commonly aimed at control of abomasal nematodes of the genera Ostertagia and Haemonchus. Use of avermectins is largely strategic in cattle, treatments being favored at the end of the period of transmission of these parasites; this frequently coincides with housing, entry into a feedlot or movement to another pasture. Simultaneous control of important ectoparasites at this time is an added benefit. Prophylactic use of avermectins at pasture is primarily targeted at the young first season grazing animal. In horses, a bimonthly treatment schedule during the period of risk has proved effective in helping prevent adverse effects of the main target parasites, including large and small strongyles and stomach bots. These patterns of use can be applied to the evaluation of the potential for avermectin residues in feces to have impact on pasture ecology. The evidence presented suggests that any effects are temporally and spatially limited. After more than a decade of practical use, there is no indication that avermectins have had a significant impact on pasture ecology and the environment.
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Beveridge, W. I. (1993). Unravelling the ecology of influenza A virus. Hist Philos Life Sci, 15(1), 23–32.
Abstract: For 20 years after the influenza A virus was discovered in the early 1930s, it was believed to be almost exclusively a human virus. But in the 1950s closely related viruses were discovered in diseases of horses, pigs and birds. Subsequently influenza A viruses were found to occur frequently in many species of birds, particularly ducks, usually without causing disease. Researchers showed that human and animal strains can hybridise thus producing new strains. Such hybrids may be the cause of pandemics in man. Most pandemics have started in China or eastern Russia where many people are in intimate association with animals. This situation provides a breeding ground for new strains of influenza A virus.
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Hardy, J. L. (1987). The ecology of western equine encephalomyelitis virus in the Central Valley of California, 1945-1985. Am J Trop Med Hyg, 37(3 Suppl), 18s–32s.
Abstract: Reeves' concept of the summer transmission cycle of western equine encephalomyelitis virus in 1945 was that the virus was amplified in a silent transmission cycle involving mosquitoes, domestic chickens, and possibly wild birds, from which it could be transmitted tangentially to and cause disease in human and equine populations. Extensive field and laboratory studies done since 1945 in the Central Valley of California have more clearly defined the specific invertebrate and vertebrate hosts involved in the basic virus transmission cycle, but the overall concept remains unchanged. The basic transmission cycle involves Culex tarsalis as the primary vector mosquito species and house finches and house sparrows as the primary amplifying hosts. Secondary amplifying hosts, upon which Cx. tarsalis frequently feeds, include other passerine species, chickens, and possibly pheasants in areas where they are abundant. Another transmission cycle that most likely is initiated from the Cx. tarsalis-wild bird cycle involves Aedes melanimon and the blacktail jackrabbit. Like humans and horses, California ground squirrels, western tree squirrels, and a few other wild mammal species become infected tangentially with the virus but do not contribute significantly to virus amplification.
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Takai, S., Fujimori, T., Katsuzaki, K., & Tsubaki, S. (1987). Ecology of Rhodococcus equi in horses and their environment on horse-breeding farms. Vet Microbiol, 14(3), 233–239.
Abstract: Quantitative culture of R. equi in the feces of dams and foals, in the air of the stalls and in the soil of the paddocks was carried out on three horse-breeding farms during the foaling season. The isolation rates of R. equi from the feces of dams from the 3 farms suddenly increased to approximately 80% at the end of March, when the snow in the paddocks finished melting, and remained at that level during April and May. The mean number of R. equi and the isolation rate of R. equi from the feces of dams on the farms were investigated for 5 weeks before and 5 weeks after delivery. During the 10 weeks, there were no differences in the isolation rate or in the mean number of R. equi from the feces of dams. R. equi was first isolated from the feces of the foals born in February and the middle of March at 3-4 weeks of age, on the other hand, it was first isolated from the feces of foals born in the end of March and April at 1-2 weeks of age. The number of R. equi in the soil collected from the paddocks used by dams during the winter was approximately 10(2)-10(4) g-1 of soil during the experiment. R. equi was isolated from the air in the stalls at the end of March and the number of R. equi in the air increased particularly on dry and windy days.(ABSTRACT TRUNCATED AT 250 WORDS)
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