Epizootiological study of bluetongue virus infection in California livestock: an overview.

An epidemiologic program was undertaken in California to study bluetongue virus (BTV) infection in domestic livestock. The study was designed to determine: a) prevalence of BTV infection, b) serotypes of BTV actively causing infection, c) seasonality of infection and d) species infected. A total of 8,751 cattle, 14,639 sheep and 4,785 goats were tested over the 3 1/2 year study. Serologically, 41% of the cattle, 42% of the sheep and 21% of the goats were positive. Virologically, 2.4% of the cattle, 1.4% of the sheep and 0.7% of the goats were viremic. One BTV isolation was made in April (sheep) and 3 in June (1 each from sheep, cattle and goats); the remainder of the BTV isolations (a total of 359) were made in the months of July through early December. No isolations were made from January through March. Four serotypes of BTV (10, 11, 13 and 17) were isolated from all species tested (sheep, goats and cattle) and Culicoides variipennis. The serotypes isolated from C. variipennis correlated with the serotypes isolated from livestock in given areas. Multiple serotypes were isolated from single herds, flocks and individual animals on single given days. In addition to multiple serotypes being isolated, extensive heterogeneity in the electrophoretic mobility of the RNA genome segments was observed. These different migration patterns (electropherotypes) were observed between and within serotypes. No single serotype could be identified by a given pattern. No clinical disease was associated with BTV infection of cattle. Clinical disease was observed in infected sheep; however, BTV was also isolated from flocks with no overt clinical signs of disease. No reproductive problems could be associated with BTV in cattle in this endemic study area; however, BTV infection of pregnant sheep appeared to be associated with abortion and birth of dummy lambs in certain flocks.

Epidemiologic study of bluetongue virus on the Tejon Ranch, California: vector, host, virus relationships.

Culicoides gnats were monitored from April through November, 1981, on the Tejon Ranch, Kern County. Levels of gnat breeding were determined by quantitative sampling of substrate from intermittent and permanent water sources. Adult populations were measured by light trap collections taken around pens holding sentinel beef cattle, dairy calves, sheep, goats and deer. Adult gnats were collected in the environs of the study area, and blood samples were obtained from sentinel animals for laboratory diagnosis and isolation of bluetongue virus (BTV). C. variipennis was 1st observed in various water sources in April, with a continuous increase in density through October. Adult populations reflected this trend in density through October. Both immature and adult gnat populations rapidly decreased in November. BTV serotypes 11, 17 and 13 were isolated from C. variipennis from August through October. BTV serotypes 11 and 17 were initially isolated from nearly all sentinel sheep, goats and dairy calves from late July through September, whereas isolates of 11 and 17 were made from only 2 beef cows and 2 deer in August and September. Sheep were the only sentinel animals that showed clinical signs of BT disease.

WHO/FAO Working Team Report: entomology.

A summary of the more important concerns of the Working Team with particular reference to bluetongue (BT) virus (BTV), is as follows: With the exception of Australia, the US, and possibly parts of Africa, there are almost no concrete data that could be used to direct control efforts against the responsible vector(s) of BTV in a specific geographic area. In Australia, a broad plan of attack yielded data that showed that members of the subgenus Avaritia are the primary vector species. It has been clearly shown that Culicoides variipennis (Coq.) is the dominant vector species for most of the US. In the Middle East and certain areas of Africa, isolations from possible vector species indicated that C. imicola K., again probably a species complex and belonging to the subgenus Avaritia, is one of the likely vectors. Except for some subgenera, the taxonomy for much of the Culicoides remains in disarray. The subgenus Oecacta for example still remains a catchall for many species. Although a number of proposals have been made for delineating the species of the C. (Monoculicoides) variipennis species complex, none have been initiated because of the lack of funds. The Working Team strongly feels that the lack of definition of important species complexes is the result of short-term planning that does not consider the fact that efficiency can be increased and a great deal of monies saved by directing control toward the specific species or populations thereof that are responsible for a problem.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of Ectiban, egg oil, Rabon, or Sevin for control of northern fowl mites on laying hens.

Two field trials were conducted on different ranches to compare acaricides for control of northern fowl mite (NFM) on White Leghorn hens. In Trial 1 Ectiban spray and dust treatments were compared to Rabon and Sevin spray-treatments; egg oil, Rabon, and Sevin sprays were tested in Trial 2. Concentration and rates of application followed label recommendations for the registered compounds. In Trial 1 Ectiban spray gave excellent NFM control; Ectiban dust, Rabon, and Sevin spray treatments resulted in poor NFM control. Egg oil and Rabon sprays gave effective NFM control in Trial 2. Sevin, as in Trial 1, gave poor NFM control. The failure of Sevin to control mites both times suggests the possibility of NFM resistance to this chemical.

Trials with chlorpyrifos (Dursban) as a systemic insecticide against the cattle louse.

Data for louse control are presented chiefly on chlorpyrifos (Dursban) 0, 0-diethyl 0-(3, 5, 6-trichloro-2-pyridyl) phosphorothioate and fenchlorphos in one trial and chlorpyrifos and famphur in three trials. These animal systemics were tested on 168 dairy calves in four herds located in three regions of the North Island, New Zealand. Louse control, following single backline, dermal applications, showed 80%, 87% and 100% with dosages of chlorpyrifos at 5 mg, 13 mg and 20 to 200 mg per kg, respectively, and 100% and 93% with dosages of famphur at 20 mg per kg, respectively. Poor louse control (24 to 58%) with fenchlorphos was expected since this compound requires two applications 14 days apart. Ovicidal effect was demonstrated with chlorpyrifos and famphur. Minor scurfing and hair loss occurred on some calves with all compounds, but hair coats were normal 28 days after treatment. Calves given 100 mg to 200 mg per kg chlorpyrifos showed signs of organophosphate toxicity from 5 mins to 90 mins post-treatment but were normal thereafter.