PIH-81
HERD HEALTH
pork
industry handbook
PURDUE UNIVERSITY
COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, INDIANA
Swine Coccidiosis
Author:
Kent Schwartz, Iowa State University
Reviewers:
Roger Billings, Lucerne Valley, California Steve Henry, Abilene, Kansas Richard Meyer, University of Illinois
Introduction
Enteric diseases in pigs are manifested as diarrhea. Diarrhea is abnormal for pigs of any age and is accompanied by economic and productivity losses. Modern technology that emphasizes sanitation and proper environment has had a major impact in decreasing the occurrence of many enteric diseases in swine, yet diarrhea in all ages of pigs remains a major problem for swine producers.

The cause of diarrhea has an infectious (bacterial, viral, or parasitic) component, the severity of which may be related to other risk factors (sanitation, environment, or nutrition). In the past, enteric diseases were age-related, but modified production methods of age-segregation and early weaning allowed diseases once limited to the farrowing house to become a concern in the nursery or even grower-finisher. An understanding of the agents of disease and their interactions with the pig and its environment aids in developing treatment and control strategies. Coccidiosis is a major cause of diarrhea in suckling pigs and occasionally causes clinical enteric disease in swine post-weaning.

Coccidiosis is the disease caused by coccidia organisms. Pigs may be infected with coccidia with no discernible disease or clinical effect. Coccidiosis was first described in 1934, but was not considered important because no disease was associated with most infections. In the 1970’s, the advent of continuous farrowing in confinement situations caused actual disease to occur and be recognized as both common and severe. Coccidia are potent and primary pathogens in suckling pigs. Several species have also been associated with severe outbreaks of enteritis in older pigs. Disease severity is directly related to the dose of offending organism ingested. Diagnostic surveys from the Southeastern states and portions of the Midwest indicate that baby pig diarrhea associated with coccidia accounts for 10% to 36% of the cases of baby pig diarrhea.
Causative Organism

Coccidia are microscopic, one-celled (Protozoa) organisms that are obligatory intracellular parasites. Most coccidia are host
species-specific and infect only their natural host. Coccidia in swine belong to eitherthe genus Eimeriaor Isospora. They differ markedly from and are much more complex than bacteria and viruses commonly responsible for diarrhea. Of the nine species of coccidia known to exist in the U.S., eight have been classified in the genus Eimeria, a genus considered only potentially pathogenic in swine. The remaining species is in the genus Isospora (Isospora suis) and is a primary swine pathogen.

Life Cycle
All coccidia have relatively complex life cycles with both asexual and sexual stages of multiplication occurring within the hosts. Infection occurs with the ingestion of sporulated oocysts (the infectious stage). Once in the pig’s intestine, sporozoites are released from the oocysts (excystation), invade the cells lining the intestinal tract and give rise to the production and release of large numbers of invasive merozoites. Additional generations or cycles of infection occur so that there is potential involvement and destruction of many of the pig’s intestinal cells (enterocytes). Large numbers of macrogametes (female) and lesser numbers of microgametes (male) stages form during this process. The microgametes are released and fertilize the macrogametes resulting in the formation of another new oocyst. Shortly thereafter, the oocysts are released into the intestinal tract and pass out with the feces. The time required from ingestion of a sporolated oocyst to the formation and release of a new oocyst, (Isospora suis), is approximately 5 days. Oocysts are shed for approximately 7 days before the infestation subsides.
Newly shed oocysts, however, are not infectious. To infect another pig, they must undergo further development (sporogany) outside the host. This process requires oxygen (air) and takes about four days but under ideal conditions of 95° F (37° C) temperature and 80% to 85% humidity the process can be as short as 12 hours. Outside the host, the sporulated oocysts are extremely resistant to environmental conditions and disinfection. Consequently, oocyts may remain viable for months until they are ingested by another susceptible pig and the cycle
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