Alok Kumar Singh1#, Snigdha Shrivastava2, Pradeep Kumar3, S. Ramesh Bhumaiyya4 and Ravi Kumar Khare1
Coccidiosis is typically caused by protozoa from the genera Eimeria or Isosporawhich invades and destroys the intestinal mucosa. However, many infections, are subclinical, the common clinical signs includes diarrhoea, fever, inappetence, weight loss, emaciation, and even death. Coccidiosis is a costly disease that affects both the liver and the gut in cattle, sheep, goats, pigs, poultry, and rabbits. Coccidiosis is less common in dogs, cats, and horses, but it can cause clinical disease.
Eimeriaand Isospora usually only need one host to complete their life cycles. Some Isospora species have facultative intermediate hosts, for which a new genus name, cystoisospora, has been proposed. Coccidiais a host-specific, and there is no cross-immunity among coccidia species. Coccidiosis is seen worldwide, most commonly in young animals housed or confined in oocyst-infested tiny regions. Coccidia are opportunistic infections, and their pathogenicity can be altered by a variety of stresses. As a result, clinical coccidiosis is more common in conditions of inadequate nutrition, poor sanitation, or overcrowding, or following the pressures of weaning, shipping, abrupt changes in diet, or harsh weather. In general, most farm animal species have a high infection rate and a low rate of clinical disease up to 80% of animals in a high-risk group may show clinical sign. Most animals between the ages of one month and one year develop Eimeria or Isospora illnesses of different severity. Older animals are usually resistant to clinical disease, however have sporadic inapparent infections. Clinically healthy, mature animals can transmit disease to young, vulnerable animals. It’s also important to understand that infected animals can consume a tiny number of oocysts and eventually shed millions of them. So, it is a disease that is commonly found in large herds of calves when there is a high concentration of coccidian oocysts in the environment. It can also damage animals on grassland. Creep-fed lambs/calves are frequently exposed to this disease.
Infection is caused by the intake of infective oocysts. Oocysts reach the environment through the excrement of an infected host, however Eimeria and Isosporaoocysts are unsporulated and so infective when passing in the faeces. Oocystssporulate and become infective in few days under suitable oxygen, humidity, and temperature conditions. The amorphous protoplasm in the oocyst develops into sporozoites within sporocysts during sporulation. The sporulatedoocyst of Eimeria spp. contains four sporocysts, each holding two sporozoites; the sporulatedoocyst of Isospora spp. has two sporocysts, each having four sporozoites. When a susceptible animal consumes a sporulatedoocyst, the sporozoites escape from the oocyst, penetrate the intestinal mucosa or other epithelial cells, and grow intracellularly into multinucleate schizonts, also known as meronts. Each nucleus grows into a merozoite, an infectious organism that infects new cells and repeats the process. Merozoites transform into either macrogametocytes or microgametocytes after a varied number of asexual generations. In a host cell, these result in either a single macrogamete or a large number of microgametes. The macrogamete turns into an oocyst following microgamete fertilisation. The oocysts are released in the faeces unsporulated and have tough walls. Not all of the various Eimeria or Isospora species that can infect a specific host are pathogenic. Clinical illness is also influenced by concurrent infections involving two or more species, some of which may not typically be regarded as harmful. Sometimes strains from the same pathogenic species can differ in virulence.
Coccidiosisaffects the intestinal epithelium and more commonly, the underlying connective tissue of the mucosa is destroyed, which leads to clinical symptoms causing diarrhoea, catarrhal inflammation, and haemorrhage into the intestine’s lumen. Tenesmus, release of blood or tissue, and dehydration are possible symptoms. Alterations in serum protein and electrolyte concentrations i.e. hyponatremia may be noticeable, although only severely affected animals show alterations in haemoglobin or PCV.
Oocysts in faeces can be detected using salt or sugar flotation techniques. The presence of significant quantities of pathogenic oocysts in the faeces is diagnostic >100,000 oocysts/gm of faeces in severe outbreaks, but diarrhoea may occur one to two days before the large output of oocysts and may persist even after the oocyst discharge has recovered to low levels, it may be necessary to perform numerous faeces examinations of one animal or a single faeces examination of animals kept in the same habitat because it is not always possible to find oocysts in a single pooled sample. The number of oocysts found in faeces depends on several factors, including the species genetic capacity for reproduction, the quantity of infectious oocysts consumed, the stage of the infection, the animal’s age and immune status, previous exposure, the consistency of the faecal sample, and the method of analysis. Faecal testing results must therefore be correlated with clinical symptoms and gross and microscopic intestinal abnormalities. Additionally, it must be established that the species is pathogenic to that host. A diagnosis of clinical coccidiosis cannot be made based solely on the discovery of many oocysts of a non-pathogenic species in conjunction with diarrhoea.
Some of the effective drugs available in the market i.e. Toltrazuril @50 mg/ml orally, Diclazuril @ 2.5 mg/ml orally for 14 days, and Decoquinate @60.6 g/kg premix in feed for 28 days.
Prevention and Control:
Eimeria and Isospora have self-limiting life cycles that, barring reinfection, die on their own within a few weeks. Prompt treatment may shorten the duration of the illness, lessen oocyst discharge, ease bleeding and diarrhoea, lower the risk of subsequent infections and death, and slow or inhibit the development of stages brought on by reinfection. When feasible, sick animals should be kept apart and treated individually to ensure therapeutic medicine doses are delivered and to prevent exposure of other animals. However, the effectiveness of any medicine in treating clinical coccidiosis has not been established, despite the fact that it is generally acknowledged that treatment is effective in preventing reinfection and should, thus, speed up recovery. Since the majority of coccidiostats have a depressive impact on the early, first-stage schizonts, they are best utilised for control rather than treatment. Calves with clinical coccidiosis are frequently given oral soluble sulphonamides.
In order to generate an infection that will elicit immunity but not clinical symptoms, prevention relies on restricting young animals’ intake of sporulatedoocysts. This objective is helped by proper management practises, including sanitation and feeding procedures. Colostrum is recommended for newborns. Young, weak animals should be housed in sanitary, dry conditions. The placement of feed in troughs that are elevated above the ground and strategically arranged to make it impossible for faeces to contaminate the feed are examples of feeding and watering equipment that should be clean and protected against faecal contamination. Stresses should be kept to a minimum, including weaning, abrupt changes in nutrition, and movement. When animals under diverse management regimes can be predicted to acquire coccidiosis, preventive administration of coccidiostats is advised. Calf buildings should be kept as hygienic as possible, including the use of suitable disinfectantsdue to the robust and long-lived nature of coccidiaoocysts. The fact that many of the disinfectants used often on farms are ineffective should be emphasised. To prevent exposure to high levels of challenge and to minimise faecal contamination, feed and water troughs should be clean and elevated from the ground. To prevent pools of water or moist bedding, beds should be kept dry and floors should have excellent falls. Plumbing needs to be kept up to prevent leaks at drinking troughs or bowls. Coccidiosis is a problem anywhere there is an accumulation of excrement in the environment. For this reason, creep feeders at pasture should be moved frequently.