Post-challenge Period Research Articles

Criteria for Examining the Immune Response to Infectious Bronchitis Virus

Immune response to infectious bronchitis virus (IBV) with different serotypes and isolates employed as vaccines, was studied by observing respiratory signs, virus infection, and blood-tinged tracheal swabs, and by the fluorescent antibody (FA) technique. Results were also compared at various times in the postchallenge (PC) period. Most satisfactory was examination of the chickens on the 3rd and 4th day PC with Massachusetts-type IBV, M41 isolate. Beyond the 4th day with chickens vaccinated with AIII and Connecticut IBV isolates, the challenge virus infection was apparently aborted and, in many instances, individual chickens became asymptomatic. In contrast, where the chickens proved immune at the 3rd and 4th day PC after previous vaccination with a Massachusettstype virus, Connaught isolate, an excellent pattern of immunity persisted through the 7th PC day, the last observation time. Resistance to infection or signs, was not altered greatly by wide variations in the dose of challenge virus administered. A higher proportion of IBVsusceptible chickens had blood-tinged tracheal swabs at the 3rd or 4th day PC. Beyond these days, the examination of swabs was unreliable. This criterion for assessing the immunity status was not considered specific enough for a precise or critical measurement. The FA technique was of value in detecting infection on the 2nd, 3rd, and 4th days PC. However, a lack of correlation sometimes oc-

Efficacy of Graded Levels of p-Ureidobenzenearsonic Acid Against Different Levels of Exposure to Histomoniasis in Turkeys 5 and 13 Weeks Old ,

WELTER and Clark (1961) reported that p-ureidobenzenearsonic acid (p-UBAA), administered continuously starting one week before infection, reduced mortality and lesions due to histomoniasis. Similar results were obtained in challenge experiments by Sullivan et al. (1964, 1965), when dietary treatments were initiated five days prior to exposure. Lund (1955) studied histomoniasis mortality as related to the size of the infective dose. He observed a decrease in mortality as the infective dose was decreased.The purpose of this study was to determine the efficacy of graded levels of p-UBAA against different levels of exposure to histomoniasis in turkeys five and 13 weeks of age.EXPERIMENTAL PROCEDURETwo challenge experiments were conducted in which turkeys were artificially exposed to embryonated Heterakis gallinae ova containing Histomonas meleagridis. Exposure was accomplished by placing the H. gallinae ova directly into the crop by means of a pipette. The post-challenge periods were 28 and 27 days for .

Long-term Studies of the Immunity in East African Cattle Following Inoculation with Rinderpest Culture Vaccine

Virus-neutralising antibody was investigated over periods of 24 to 50 months in East African cattle which had been inoculated with culture-attenuated rinderpest virus of 91 or more passages in calf kidney monolayers. The cattle were of 3 types, viz: Friesian or fersey grades, Boran (shorthorn zebu) and Ankole (longhorn). Grade cattle showed a peak mean antibody titre of 102.17 at 4 weeks, but a considerable decline occurred between 12 and 18 months after inoculation; in the following 3 years little additional change took place. A few animals had very low titre antibody after 6 to 12 months, but this was probably associated with the presence of minimal quantities of passively-acquired antibody at the time of vaccination. When 3 such cattle were challenged after 27 and 37 months, 2 developed inapparent reinfection, with a delayed serological response, beginning on the fifth day. Two other animals showed a rapid anamnestic response reaching a peak within 48 hr.; one of the latter probably injected arinderpest-susceptible ox which was housed with it during the post-challenge period. Four grade cattle which were challenged after 50 months showed no clinical or serological reaction. Boran cattle produced a high mean antibody level 0f about 102.0 which persisted until the end of the second year, while any fall thereafter was very slow. Of the individual animals, only 26% showed a decline > 1 log10 unit in the first 3 to 4 years, compared with 46% among the grades. Not one of 56 vaccinated animals was serologically negative at the end of 3 1/2 years. In the Ankoles, no significant decline in mean antibody titre occurred during the first 2 years of the experiment but, as in other groups, there was great variation in the peak titres attained in different individuals (100·6 to 102·8). The rate of decline of antibody and the resistance to challenge of animals with very low titres makes it probable that rinderpest culture vaccine confers a lifelong immunity. Nevertheless, "immune" cattle with very low levels of circulating antibody may contract inapparent reinfection, thus becoming transitory "carriers" of virulent rinderpest virus.

Inhibition of Development of Dictyocaulus filaria as an Expression of Immunity Attained in Sheep

A high degree of immunity (81.8%) against thread lung worm, Dictyocaulus filaria, in sheep was obtained by double vaccination. The antigen of this vaccine, infective larvae, was attenuated at a level of 40,000 r, X rays of roentgen origin or gamma rays of Co'. Immunity was indicated by noticeable differences in: (a) the average number of larvae/g of feces/reproductive female recovered within the entire postchallenge period (0.07 : 1.40); (b) the number of parasites (24.1 : 168.8); (c) the relative mortality ( 0: 12.5% ); (d) the degree of clinical and pathomorphological changes, and (e) the degree of inhibition of parasitic development in general, but of oogenesis especially, comparing vaccinated immune animals with nonvaccinated controls. Studies of the possibility of immunizing a host against some species of parasites have great scientific and practical significance. Successful immunization against parasitic diseases could be a suitable method for their prevention, and in certain cases, could lead to their