Coccidiosis is a herd health problem caused by a parasite in the gut. The severity of coccidiosis is dependent on the parasite species and stage of infection. The economic losses due to coccidiosis is variable, but ranges from 5 points feed conversion in a mild case to 15 points in severe cases.
The pathogen
Coccidiosis is commonly used to describe a protozoan parasitic infection caused by Eimeria species. In poultry, about 7 species are described of these host specific parasites. In broiler known pathogenic species are Eimeria acervulina, Eimeria maxima, Eimeria tenella and possibly Eimeria mitis. Infections with multiple species is often seen. The Eimeria oocysts (“eggs”) are highly resistant to most disinfectants and are able to survive for multiple years in the environment.
Life cycle
The complete life cycle of Eimeria species takes between 5 and 7 days. Practically this means multiple cycles will always occur, in even short-lived poultry species. Starting with the uptake of oocysts (“eggs”), the outer layer is broken down inside the upper digestive tract and the parasites are released into the gut. The protozoans penetrate the mucosal layers protecting the gut and start to replicate in the intestine wall. Usually, the host will develop an immune response suppressing further infection. The cycle ends with the Eimeria developing new oocysts. Due to the short and efficient life cycle, one infected host will secrete millions of oocysts in a matter of weeks. Most poultry houses are therefore heavily contaminated with oocysts at the end of the rearing period.
Pathogenesis
Eimeria species are always present in poultry houses. Even with optimal disinfection, it is likely some oocysts will survive. Coccidiosis will only result in clinical disease when either the environment is heavily contaminated with oocysts or the immune system fails to suppress the infection. In broiler, clinical coccidiosis occurs often between day 21 and 35 with a peak occurrence around day 28. The severity of the infection is dependent on factors such as Eimeria species, strain, gut health and the dose of ingested oocysts. Underlying viral infections, such as Infectious Bursal Disease (IBD) (Gumboro), repress the immune system and contribute to the severity of clinical coccidiosis. Factors that decrease gut health also play an important role. Damage to the gut wall caused by coccidiose is a known risk factor for Clostridium spp. overgrowth in the gut, resulting in even bigger losses.
Clinical coccidiosis
Most cases of clinical coccidiosis include reduced feed intake and wet litter due to dysbacteriosis. There are some specific signs dependent on Eimeria species causing the infection.
– Eimeria acervulina: located in the first part of the small intestine, this Eimeria infection is often somewhat chronic. The animals typically have slightly bleaker combs, reduced daily growth and less efficient feed conversion.
– Eimeria maxima: located in the middle region of the small intestine, Eimeria maxima has a variety of clinical signs. Growth retardation, wet litter, enteritis and in severe cases increased mortality.
– Eimeria tenella: located in the caeca, Eimeria tenella is responsible for the highest economic losses. Increased losses, enteritis, bloody manure, severe growth retardation and wet litter. Mortality often occurs suddenly and can reach loss percentages of more than 10%.
Prevention
Coccidiosis is a herd health issue where the main goal in prevention lies in reduction of poultry house oocyst contamination and optimizing herd immunity and gut health. After optimal cleaning and disinfection of the poultry house floor, the initial amount of oocysts should be minimal. To slow down the coccidiosis cycle, coccidiostats are mixed into the feed.
Furthermore, an effective vaccination schedule should be in place to provide optimal protection against (viral) diseases that could reduce the efficiency of the immune system against coccidiosis. By maintaining optimal gut health, the bird’s own immune system should be able to develop a sufficient immune response. Although coccidiosis is a very common herd health problem, optimal prevention is complex and highly farm-specific.
Consultancy
The Health Center for Poultry (GvP) has broad experience dealing with coccidiosis. Our experience tells us that every farm needs a customized workable approach. For more information on coccidiosis or a second opinion, please contact us.
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