Epizootiological Studies Research Articles

Regulatory Activities Concerned with Development of Avian Encephalomyelitis Vaccine

Avian encephalomyelitis (AE) is a virus disease of chickens first observed in 1930 by Jones. Since egg transmission was an indicated source of infection, larger breeding establishments investigated, during the early 1950's, methods of prevention and control. The Animal Inspection and Quarantine Division was first contacted in 1956 regarding a U. S. Veterinary License for avian encephalomyelitis vaccine. The mode of natural transmission and true incidence of the disease had not been determined. Prospective license applicants were discouraged by work required to establish the safety and efficacy of experimental products prior to licensing. Meanwhile the Animal In'spection and Quarantine Division, cognizant of the research efforts and the results, had permitted several interstate shipments of brain-propagated live avian encephalomyelitis vaccine for investigational use. The limited field studies conducted were inconclusive because of failure to provide unvaccinated controls and to check immunity of vaccinates and their progeny by challenge or laboratory procedures. The majority of requests made by individuals who simply wanted to u'se the vaccine and had no desire to conduct a controlled field study were denied. These poultrymen were forced to continue to risk the hazards of AE or find another source of vaccine. Commercial manufacturers of biologicals were not interested in preparing avian encephalomyelitis vaccine. Epizootiological studies established that AE was widespread in the United States and Canada. This work also presented convincing evidence that the progeny of immune flocks did not show as chicks clinical evidence of infection. The demand for AE vaccine increased in 1960. Routine interstate movement of unlicensed vaccine could not be permitted. As a result of a meeting with researchers working on avian encephalomyelitis, it was concluded that live virus vaccine propagated in chicken embryos appeared to offer the greatest advantages. Prospective licensees agreed to withdraw pending license applications for chicken brain-propagated live virus vaccine. Efforts were directed toward stimulating interest by a biologies manufacturer, further evaluating live virus vaccine propagated in chicken embryos, and investigating the incidence of the disease in progeny of resistant flocks. Permits for interstate shipments were granted only for the purpose of evaluating experimental product for licensing. The objectives proposed for field trials included studies on the spread of vaccine virus through the egg and by direct contact to susceptible birds and, if such

Bacterins and Drugs for the Control of Experimental Fowl Cholera

FOWL cholera, caused by the bacteria Pasteurella multoctda, is one of the oldest poultry diseases studied. In fact, in 1880 Pasteur grew this organism in pure culture and used it in some of his fundamental experiments in the attenuation of bacteria. Much research has been done on controlling this disease by immunization, but no real progress was shown until 1958.6 Certainly the major problem with this disease in flocks has been its chronic nature. Recent11 work in Russia showed that the organism is difficult to kill under natural environmental conditions. The organism survived 2-4 months in fowl carcasses left out-of-doors in the winter at -25?C to 2?C temperatures. In buried carcasses it survived for 5 months. In spring at temperatures of -13.5 to +22?C, it survived 3-4 months in the heart, liver, and spleen, and 2-21/2 months in the intestines. In summer, at 8-29?C, it survived for 25 days in exposed carcasses and for 3 months in buried carcasses. Research in South Dakota4 has indicated that most outbreaks were acute. Epizootiological studies suggested older birds as the carriers and most probable source of infection in young birds. The researchers were unable to immunize birds with a chick embryo vaccine inactivated with formalin. They found that oxytetracycline (Terramycin; Pfizer) was the most effective of the antibiotics they tested against experimental fowl cholera infections.

Haemagglutination and haemagglutination-inhibition with African horse-sickness virus.

COMPLEMENT-fixation and mouse neutralization tests are the two techniques so far employed in serological work with African horse-sickness virus. It was thought worth while to study the haemagglutinating properties of this agent with the view of obtaining yet another tool for epidemiological (epizootiological) studies of this dreaded horse disease.

Studies on the epizootiology ofNematodirusinfestation in sheep in New Zealand

Summary Epizootiological studies over a three-year period have shown a remarkable regularity in the occurrence and course of Nematodirus infestation in lambs. Observations of larval populations on pasture have shown the presence of a small larval peak in the spring followed by a larger peak in the autumn. A trial conducted in the autumn of 1959 has shown the importance of the autumn larval peak with regard to susceptible animals. Differences were found to occur in the duration of spring- and autumn-acquired infestations, and evidence is presented indicating that older sheep do possess some measure of 2ge resistance to Nematodirus infestation.

昭和23年夏流行したブタの死産の疫学的研究

昭和23年夏流行したブタの死産の疫学的研究