Concurrent infections with reoviruses and coccidia in broilers.

These experiments investigated the interaction among two species of coccidia (Eimeria acervulina and E. mitis) and three strains of reovirus (virus 2035, a weak to moderate pathogen; and viruses 2408 and 1733, severe pathogens). When reoviruses were not present, high inoculation dosages (10(6) sporulated oocysts/bird) of both E. acervulina and E. mitis depressed weight gain, plasma pigment, and plasma protein. Low doses of coccidia (10(4) oocysts) in the absence of virus had no such effect on weight gain. When high doses of coccidia were present at the same time as virus 2035 or 2408, they resulted in a significantly greater depression of weight gain than when either virus or coccidia were present alone. With virus 2035, this greater depression was seen even when low doses of coccidia were used. Lesion scores due to coccidiosis and the number of oocysts produced were not affected by previous exposure to reovirus. Both coccidiosis and reovirus infections increased the frequency of some leg problems and other abnormal conditions. The most obvious interaction between coccidia and reovirus was the marked increase in swollen hocks seen when coccidia and virus 2035 were present together (20-27%) compared with either the virus or coccidia alone (0-10%). Virus 2408 interfered slightly with the development of immunity to coccidia. There was some indication that early coccidiosis could increase the ability of some virus isolates to infect various tissues of the host.