Epidemiology of Ostertagia in the Northwestern USA.

The two most significant environmental factors that influence the epidemiology of Ostertagia are temperature and moisture. These factors vary more in the west and northwest than in any other part of the USA because of extreme regional differences in climate, topography, and land use. Consequently, patterns of Ostertagia transmission and inhibition also vary widely from region to region and from year to year. Recent data require revisions of previously accepted concepts of northern/southern transmission and inhibition. In particular, the flaw of liberal extrapolation of information from one region to another has now been recognized. Inhibition may not occur along the coast of the Pacific Northwest. Although not completely delineated, the transition zone between northern and southern patterns of inhibition appears to be significantly wider and more variable than previously recognized; Oregon data suggest a possible indeterminate and variable band extending north of the 45th parallel and south of the 43rd parallel. Summer inhibition has now been documented in areas of Oregon and Montana. Other than the recent Oregon and Montana studies, data on this transition zone in the Rocky Mountain region and high plains are sparse to non-existent. In contrast to previously accepted doctrine, the fall rise in egg count generally exceeds the traditionally accepted spring rise in many areas. From the Pacific Northwest to the Midwest, year-round transmission patterns have been observed. The presence of geothermal ground water sources produces microclimates that favor larval survival in many areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of Montana and Alaska isolates of Echinococcus multilocularis in gerbils with observations on the cyst growth, hook characteristics, and host response.

To assess its biological distinctness, an isolate of Echinococcus multilocularis from Montana was compared with an isolate from Alaska in gerbils (Meriones unguiculatus) by means of intraperitoneal inoculations with protoscoleces. The cysts formed by the Montana isolate were entire, hyaline, and translucent, whereas those produced by the Alaska isolate were granular, yellowish, and opaque. Vesicles of the Montana isolate were larger, produced protoscoleces more slowly but in greater numbers, and required a longer period to develop surfacial germ cell protrusions, which were of smaller size. Also delayed was invasion of the laminate layer by granulocytes and macrophages, and a longer time was required for the appearance of pulmonary metastases. The 2 isolates differed also in characteristics of rostellar hooks, those from the Montana isolate being fewer and larger, often with accessory hooks.

Distribution and seasonal prevalence of bovine lungworms in selected areas in western Montana.

In a survey (Oct, 1967, through Aug, 1969) of the distribution and seasonal prevalence of bovine lungworms in beef herds in 3 western Montana counties (Park, Gallatin, and Ravalli), infected cattle were detected in 27 of 35 herds. Results of 2,125 fecal examinations indicated that 7.8% of all cattle were infected with Dictyocaulus viviparus. Lungworms were found in 6.6% of 1,038 calves (less than 12 months old), 11.5% of 755 yearlings (1 to 2 years old), and 3.3% of 332 cows (more than 2 years old). A distinct seasonal pattern existed in calf infections, with initial passage of larvae beginning in late July or August and persisting until November or December. Exposure of calves in 1 portion of the study area apparently was delayed until November, with patent infections continuing through March. Spontaneous loss of infections normally occurred after 3 to 4 months of patency. The mean rate of larval excretion in the feces of all infected cattle was 0.37 larvae per gram of feces (l/g). Larval output was relatively uniform within each geographic area regardless of host age, but varied considerably from one portion of the study area to another. The potential role of wild ruminants (deer, elk, and moose) in the epizootiology of D viviparus is discussed with respect to western range utilization practices.

Observations on the life cycle and prevalence of Eimeria leuckarti in horses in Montana.

Of 22 foals from 4 localities in southwestern Montana, 59% were found to be infected with Eimeria leuckarti. Oocysts collected from feces of 4 positive horses were sporulated and subsequently administered to a 5- to 6-month-old foal. The prepatent period was 31 days and the patent period was between 5 and 10 days.

Observations on epizootiology and distribution of Elaeophora schneideri in Montana ruminants.

Seventy-four moose, 111 elk, 20 mule deer, 8 white-tailed deer, 26 prong-horn antelope, 42 domestic sheep and 3 bighorn sheep from Montana or northwestern Wyoming were examined post-mortem for evidence of Elaeophora schneideri infection in 1973-74. Fifteen percent of the mule deer and four percent of the moose were positive for adult arterial worms. This constitutes the first report of E. schneideri in mule deer in Montana. No gross signs of blindness or other neurologic disorder were evident in the infected animals. Potential horsefly intermediate hosts collected in the enzootic area included Hybomitra rhombica osburni, H. tetrica, H. metabola, Chrysops noctifer pertinax and Atylotus incisuralis.

Use of fenbendazole for long-term control of protostrongylid lungworms in free-ranging Rocky Mountain bighorn sheep.

In an effort to control Protostrongylus spp. in a Rocky Mountain bighorn sheep herd (Ovis canadensis canadensis) of approximately 30 animals, fenbendazole-medicated salt was placed on the Stillwater bighorn winter range in southcentral Montana (USA) for four consecutive winters, 1990 to 1993. Sheep of all age and sex classes were observed using the medicated salt throughout the study period. Prevalence and average number of lungworm larvae per gram of bighorn feces declined significantly (P < 0.05) from pretreatment levels (1987 to 1989), and remained low throughout the study period. Free-choice availability of fenbendazole-medicated salt is a potentially effective management tool for long-term control of protostrongylid lungworm.

Studies on pronghorn antelope (Antilocapra americana) as reservoirs of anaplasmosis in Montana.

Twenty-six pronghorn antelope (Antilocapra americana) were collected in an area of eastern Montana where bovine anaplasmosis is enzootic. Their sera were examined for evidence of anaplasmosis by the complement-fixation test. Strong false positive reactions (3+ and 4+ reactors) occurred for 19 of the sera tested; 6 sera were anticomplementary. Inoculation of antelope blood into anaplasmosis, and anaplasma bodies were not found in stained blood smears of antelope or recipient calves.

Trichinella sp. in wolves from interior Alaska.

Tongue samples were collected from 148 wolf (Canis lupus) carcasses during 1993 and 1994 near Fairbanks (Alaska, USA). A standard peptic digestion procedure was used to detect Trichinella sp. larvae. Larvae were found in 54 of 148 (36%) samples. There was no significant difference in sex-specific prevalence. Prevalence was significantly related to age. There was no relationship between the number of larvae/g of host tissue and the age or sex of the host. Trichinella spp. infection may cause illness in individual wolves. However, there was no indication the parasite had any impact on the population.

Survival of sylvatic Trichinella spiralis isolates in frozen tissue and processed meat products.

The ability of Trichinella spiralis larvae to survive at subfreezing temperatures encysted in the musculature of wild carnivorous mammals was assessed by evaluating motility and infectivity (to rodents) of trichinae at various intervals after storage in frozen skeletal muscle. Fifty to 60% of the larvae in grizzly bear meat were alive after storage for 27 months at -6.5 to -20 C, and 30% to 50% were still alive at 34 months. However, none survived for 38 months, on the basis of infectivity in mice and larval motility. Trichinella larvae survived up to 4 months in frozen (-6.5 to -20 C) wolverine tissue. Viable larvae were not recovered from mountain lion or fisher muscle frozen for 1 month. The effect of postslaughter processing on Trichinella larvae encysted in bear meat was evaluated by use of a similar bioassay procedure. Viability of larvae recovered from black bear meat that had been processed into ham or jerky was not affected by dry curing with a commercial salt mixture. Trichinae from both preparations induced infections in mice (58 to 90 larvae/g of tissue). However, a combination of curing and smoking was consistently lethal to encysted larvae. Viable trichinae were not recovered from ground bear meat preparations (pepperoni, salami, or sausage) processed according to commercial standards.