COCCIDIOSIS IN POULTRY

Coccidiosis is an ever-persistent threat to the poultry industry. It is a disease that affects mostly young chickens at age of three to twenty weeks. It may however occur in two weeks old birds occasionally. With the latest preventive measures in the poultry industry, the problems caused by chicken parasites have been radically reduced. The steps taken to prevent these range from keeping chickens in closed housing, on single caged sites, and operations under high levels of biosecurity (safety from microorganism which can be infectious). Parasites like flukes, round worms and tapeworms have an intermediate (secondary) host. Thus by controlling these intermediate hosts, a high level of control of the parasites can be achieved. Ectoparasites on the other hand can be transmitted by contact. However the single-celled protozoan parasites that cause coccidiosis adapt readily to changes in poultry management plan and had become one of the most important pathogens of chicken. It has been estimated that worldwide, the disease and control measures cost around USD 1,000 million yearly.
                                              CAUSES OF COCCIDIOSIS.
Coccidiosis are caused by several species of Eimeria which have specific predilection site on the intestinal mucosa. They include: E. acevulina and E. Praecos with predilections at the upper intestine; E maxima at the mid gut; E. mitis at the distal 2/3 of the intestine; E. brunette at the lower intestine and colorectum and E. tenella which has characteristic hemorrhagic lesions in the ceca. Also the least common E. necatrix causes hemmorhagic lesion in the mid gut. Mortality due to coccidiosis is almost always caused by E. tenella or E. necatrix. E. maxima and E. brunette interfere with performance of birds and only cause death with secondary bacterial infection. Infections with E. acevulina and E. mitis are the most common and insidious affecting intestinal absorption of nutrients leading to poor weight gain and feed conversion. Concurrent infection with more than one Eimeria species usually occur and is usually common in case of coccidiosis. Once a species has affected a site, it becomes very difficult to eradicate since with their relatively simple life cycle, they can multiply to give numerously highly resistant oocysts which are excreted in the feaces into the litter. Some of these oocysts are even very resistant to chemicals during routine cleaning of the poultry house thereby leading to persistence in the poultry house. Once chicks start picking the oocysts, it multiplies rapidly to an extent that without anticoccidial drug, clinical disease will certainly occur.
                                              LIFE CYCLE OF EIMERIA
The life cycle of this Eimeria can be divided into stages for easy comprehension.
STAGE 1- INFECTION. After excretion of the oocysts, under favourable conditions of temperature and humidity (air moisture and warmth), the oocyst sporulates at about 24-72 hrs post excretion. The sporulated oocysts once in the crop digests off the protective wall and release the sporocysts which in turn split to liberate two sporozoites. These then migrate to the intestine and specifically to the zone of predilection for the infecting species and invade the mucosal cells.
STAGE II- MULTIPLICATION.  The sporozoite undergoes transformation before starting the asexual division resulting in the formation of a schizont containing merozoites. The schizont ruptures to release the merozoites which infect further cells. This cycle may repeat three or four times depending on the species which result in multiplicity of infecting merozoites. The amount of such merozoites will then determine whether or not clinical coccidiosis will occur. When it does occur, the signs include droopiness, anorexia, weakness, hurdling to heat source, depression and the vent will be soiled with bloody to chalky or yellow diarrhoea.
STAGE III- MATURATION. After the last cycle of multiplication, the merozoites infect other cells and undergo sexual division giving rise to gametes which may be micro or macrogametes depending on whether they are male or female gametes respectively. Their fusion then results in the production and release of  oocysts produced depending on the amount of oocysts ingested and the species of Eimera.
                                           DIAGNOSIS OF COCCIDIOSIS.
This is based on identification of specific lesions in the intestine, demonstration of developing schizonts or oocysts in mucosal smears. Disease diagnosis is based on the presence of oocysts in the intestinal lumen.
                       CHEMOTHERAPEUTIC CONTROL (ANTICOCCIDIAL DRUGS).
 The use of sulfonamides and potentiated sulfonamides has been in use successfully against coccidiosis for over five decades. Eventually, many drugs were developed for continuous in-feed administration for broilers, and breeders and layers during rearing. Due to development of resistance and inherent toxicity of these sulfa-drugs, their use has been restricted in some areas. However in our locality due to their relative low cost and availability, they are the anticoccidial drugs of choice. Amprolium, and Nicarbazine both developed in the 1950s are very useful. Development of the polyetherionophores is of great assistance (Eg. Monensin which was first produced in the early 1970s, and salinomycin etc.) . Their long term utilization is due to less tendency to development of resistance in chicken. Because ionophores are not 100% effective, they are rather useful in the control of oocysts build up in the liter. Irrespective of the variation in use of ionophores in various region, their combination with chemicals (sulfonamides) are generally established in shuttle programmes of therapy. The shuttle programme combines the advantages of both drug groups and also minimizes the risk of development of resistance, thereby preventing promiscuous use of drug.
                                   IMMUNOLOGICAL CONTROL (VACCINES).
The use of vaccines in control of coccidiosis was conceived when it was demonstrated that immunity to reinfection occurs in birds recovering from coccidiosis. However, this immunity is highly species specific. Thus vaccines need to contain the various species of Eimeria that are likely to cause the disease (polyvalent vaccines). Various vaccines have been produced based on the afore stated premises. The first vaccines COCCIVAC was developed in 1952. It contains the virulent oocysts. Also more recently IMMUCOX, a similar vaccine was also produced in 1985. Since these vaccines are live (not attenuated), records of clinical coccidiosis following administration has been recorded. This is because oral route of administration may result in unequal exposure with some birds remaining susceptible and others with clinical disease. Therefore, drug treatment is sometimes necessary to control the vaccine. The first attenuated vaccines called PARACOX is now obtainable and is widely used in Europe. They contain seven attenuated Eimeria species. They produce few oocysts and do not cause clinical disease, yet induce or stimulate a protective immune response. The PARACOX utilization has modified the clinical picture of coccidiosis in broiler breeders with excellent protection and better flock uniformity. More recently, LIWACOX another attenuated vaccine has been produced and used especially in European countries. In Nigeria, the utilization of these vaccines has been impeded because of the presence of numerous low scale poultry production (subsistence farming), cost of these vaccines is also a factor for the fact that these vaccines are not thermostable, with recurrent cases of vaccine failure. However, in larger establishments where use of these vaccines are relatively cost effective, they can be used. In Nigeria, Immucox, a live vaccine is being marketed by Animal care service Konsult; however, the high dosage vial has really slowed down its patronage by the local and small scale farmers due to the relatively high cost. This has made the chemicals (Sulfonamides) more affordable and less expensive to use for the chemoprophylaxis and chemotherapeutic control and management of coccidiosis.
                                                        SUMMARY.
With current advances in development of vaccines with the objective of controlling the incidence and devastating economic losses encountered in coccidiosis, hopefully in some years to come the term Coccidiosis with its attached enigma in poultry production may be close to being forgotten. Meanwhile, right now the best option for the farmer is to institute managemental precautions and procedure for controlling coccidiosis.