Coccidiosis

Diarrhoea is the main sign. Heavily infected young ruminants pass foul-smelling diarrhoea with mucus or blood, lose appetite, strain, and become weak, dehydrated and painful in the abdomen. Chickens show bloody diarrhoea, weight loss and deaths, while milder subclinical enteritis quietly depresses productivity. Chronic cases have poor coats, stunted growth and poor feed conversion. At necropsy the affected gut segment is thickened, congested and oedematous with pinpoint or larger haemorrhages, and in chickens lesion scoring by segment gauges severity. Histology shows villous atrophy with inflammatory cell infiltration.

Coccidiosis is intestinal disease caused by single-celled, obligate intracellular protozoa: Eimeria species in livestock and poultry, and Isospora (Cystoisospora) species in dogs and cats. Almost every species is host-specific, and immunity to one gives no protection against another. An animal swallows sporulated oocysts; the released stages invade intestinal epithelial cells, multiply asexually through repeated generations that burst the cells, then reproduce sexually to form new oocysts passed in faeces. One oocyst can yield millions of offspring. The destroyed lining leaks fluid, protein and blood, villi atrophy, and digestion and absorption fail. Damage to the large intestine produces more severe disease than small-intestinal infection. Chickens host seven Eimeria species, each living in its own section of the gut with its own level of pathogenicity.

Coccidia infect birds, mammals and reptiles. Transmission is faecal-oral: oocysts need moisture, oxygen and warmth to sporulate, which takes one to two days for fresh poultry oocysts and up to weeks in other settings, and they can survive a year or more in the environment. Young animals are most at risk, especially lambs and kids around weaning, while older animals develop immunity and usually show no signs. Crowding, weaning, shipping, poor sanitation, poor nutrition, concurrent disease and corticosteroid use all tip infection into disease; in poultry, flock density, dose and host genetics also matter. The disease is a major economic burden in poultry, and resistance to anticoccidial drugs has grown with their extensive use.

Other causes of diarrhoea in young animals must be excluded: bacterial, viral and other parasitic enteritis, nutritional deficiencies, and feeding or management faults. In chickens, necrotic enteritis and other parasitic diseases are the main look-alikes. Finding oocysts alone is not enough: very high faecal counts in an outbreak, or moderate counts with matching signs, support the diagnosis, and the severity of diarrhoea may not coincide with peak shedding. Species identification by oocyst morphology, after sporulation if needed, and the pattern of gut lesions confirm it.

Small intestine, caeca, large intestine and colon, intestinal epithelium and villi

Clean, dry housing and litter; raised feeders and water troughs; avoid crowding and stress; enough colostrum; isolate sick animals. Anticoccidials in feed or water where disease is predictable. Live vaccines exist for poultry only.

Mortality is generally low and disease is often self-limiting within weeks with supportive care and less stress (MSD), though untreated cases in poultry cause deaths. Chronic cases may stay stunted with poor feed conversion.