Coccidiosis is a common protozoan disease with considerable economic losses due to malabsorption, bad feed conversion rate, reduced weight gain and increased mortality. It is characterized by enteritis and bloody diarrhea.
It is caused by protozoa parasites called Eimeria which infect various sites in the intestine. Poultry coccidia are generally host specific and different species parasitize specific parts of the intestine. Eimeria necatrix and Eimeria tenella are the most pathogenic in chickens. They cause extensive haemorrhage in small intestine and ceca and this is because schizogony occurs in the lamina propria and crypts of Lieberkuhn respectively. Other Eimeria species are E.maxima, E.acervulina, E.brunetti, E.mitis. In Turkeys- E.adenoides, E.dispersa, E.meleagrimitis.
The infectious process is rapid (4-7 days). The stages of coccidia appear both within the host as well as outside. Oocyst under proper conditions of temperature and moisture develops within one to two days to form a sporulated oocyst which is capable of infecting other chickens. This is then eaten up by a chicken and enters a cell in the chicken’s intestine. When sporozoites (oocyst containing 8 bodies) enter the cells, they divide many times producing merozoites. Each merozoite in turn enters another intestinal cell. As multiplication continues, large numbers of intestinal cells are destroyed. Eventually the cycle stops and sex cells are produced. The male fertilizes the female to produce an oocyst which from the intestinal cells and passes in the droppings. Thousands of oocysts may be passed in the droppings of an infected chicken. Birds get infected when they are reared under conditions that permit the build up of infective oocysts in the environment. Young chickens pick up the infection from contaminated premises (house, soil, wet areas etc) by other young infected birds. Both clinical infected and recovered birds shed oocysts in their droppings which contaminate feed, dust, water, litter and soil.
Infected birds tend to huddle together, have ruffled feathers, reduced appetite, depression, drooping are watery to bloody resulting in dehydration and poor weight gain and mortalities. The severity depends on the age of birds, Eimeria species, number of sporulated oocysts ingested, immune status of the flock and environmental management.
The lesion depend on the degree of inflammation and damage to the intestinal tract which include thickness of intestinal wall, mucoid to blood- tinged exudates, petechial haemorrhage, necrosis, haemorrhagic enteritis and mucous profuse bleeding in the ceca. The tissue damage in the intestinal tract may allow secondary colonization by various bacteria. E.tenella infection are found only in the ceca and recognized by accumulation of blood in the ceca and by bloody droppings. Cecal cores which are accumulations of clotted blood, tissue debris and oocysts may be found in birds surviving the acute stage. E.necatrix produces major lesions in the anterior and middle portions of the small intestine, small white spots usually intermingled with rounded, bright or dull red spots of various sizes can be seen on the serosal surface.
Coccidia can be confirmed by demonstration of oocysts in faeces or intestinal scrapings. Their location in the host and appearance of lesions are used in determining the species present. Severity of lesions, morbidity, daily mortalities, reduced feed intake, and faeces presentation are important for diagnosis. A definitive diagnosis is made through gross lesions and serosal examination during necropsy.
TREATMENT AND CONTROL
• Use of Anti-coccidial drugs under supervision by Veterinarian for treatment and prevention are available. It can be given orally or mixed with feed. This can limit high levels of infection.
• Vaccination is also available and is to be given to chicks at the early days of life (before 7 days). It should also be used under supervision by Veterinarian.
• Managemental practice includes avoiding wet litter because wet litters promote sporulation, stir litter frequently, and avoid overcrowding. Birds that are separated from their droppings have less infection.
Dr Bukola Alaba
Farmergiant Nigeria Limited