Coccidiosis is a disease causing significant losses in the poultry sector. It has been one of the conditions of the greatest economic significance as it has not been satisfactorily controlled. There are several ways to control the disease. This article will try to describe the most important ones and at the same time to show modern ways of prophylaxis and treatment of this infection.
Coccidiosis is a parasitic disease, caused by Eimeria spp protozoa. About a dozen Eimeria spores have been isolated in hens and turkeys, but in pathology the most significant are the following: E. acervulina, brunetti, maxima, necatrix, tenella, mitis and praecox in hens as well as Eimeria adenoides, E. meleagrimitis, E. gallopavonis, E. dispersa, E. subrotunda and E. dispersa in turkeys. Coccidia life cycle covers seven days. This parasite needs no intermediate hosts for its development. What is more, its high resistance to environmental conditions, fast and intensive multiplication as well as easy transmission through different vectors makes it difficult to control and stop its spreading.
The infection is usually caused by swallowing infectious oocysts present in the birds’ environment. This is the only infection route since transovarial infection is not possible. Having reached the duodenum oocysts release their invasive forms – sporosoids. The low pH of this segment’s gastric content and digestive enzymes promote the release. The released sporosoids penetrate intestine enterocytes, transform into first generation schizonts and therefore start agamic part of their life cycle – the schizogony. As the result of further divisions, first generation merozoites, second generation schizonts and second generation merozoites develop consecutively. First and second generation merozoites are able to leave enterocytes, which cause damage to these cells. Released second generation merozoites re-penetrate enterocytes, where gametocytes (micro- and macrogamets) develop starting at the same time the gamic part of their life cycle – gamogony. As the above mentioned cells conjugate and transform into the zygote (oocyst), this is excreted to the environment with the faeces.
Disease symptoms
Disease severity and clinical image depend on multiple factors. The basic factor is the type of the parasite which infected the bird, its pathogenicity and the quantity of oocysts which have been digested. The infection may be caused by one Eimeria spore but mixed infections are often diagnosed. Factors promoting the infection and severing its course include mainly: young age of birds, concomitant infections causing immunosuppression (Marek’s disease, Gumboro disease, infectious chicken anaemia viruses, reoviruses, adenoviruses) or Clostridium spp. bacteria, improper hygiene conditions (excessive livestock density, improper bedding quality, too high ammonia concentration, lack of thermal comfort), deficient nutrition (vitamin A, C, E and selenium deficiencies), and mycotoxins in the feed. Three forms of coccidiosis are listed clinically: acute, chronic and subclinical ones.
Prophylaxis and treatment
The basic prophylactic method is to make it impossible for the coccidia oocysts to develop and spread. This may be obtained by maintaining proper hygiene conditions on the farm and at the same time decreasing the oocysts’ survival rate and their possibility to transform into invasive forms. The second extremely significant element of coccidiosis prophylaxis is the effective disinfection of farm buildings before placing the birds there. Dedicated products are available on the market but the preparation Kilcox Extra should be particularly considered. Its active substance is the synthetic phenol (chlorocresol) combined with aldehyde.
Coccidiosis chemoprophylaxis is almost exclusively related to the addition of chemical or ionophoric coccidiostat drugs to chicken feed. However, too long administration of these substances limits their therapeutic capabilities since the local resistance to the most common coccidiostat drugs is more and more often diagnosed. There are ways to limit the resistance by introducing a so-called rotation program. It is based on the changes of coccidiostat drug from one group (chemical or ionophoric one) into another one, from the other group. What is more, one and the same product should not be administered too long, and upon the end of its readiness to be fed, a long enough break should be applied. Another possibility is vaccinating production flock hens. Live vaccines containing attenuated and nonattenuated strains, or subunit vaccines are used. The vaccines may be administered in the breeding unit (large drop method) or on the farm (with drinking water or in the feed spray). It is also possible to administer the vaccine to the eye on the 18th day of incubation. In case of prophylactic vaccination, do not administer the coccidiostat drug with the feed, sulphonamides and tetracyclines and the vaccinated birds must be in a good condition and have appropriate environmental conditions.