Coccidiosis is a protozoan economic disease of poultry, in which around 80% of losses are due to mortality, reduced weight gain, inefficient feed conversion, associated with loss of egg production in layers. The pathogenicity of Eimeria spp. organisms, in various poultry breeds, is documented. Control programs of this economic disease included poultry house management, introduction of live vaccines (non-attenuated and attenuated), development of subunit, recombinant, DNA-based vaccines, and supplementation of feed by prophylactic coccidiostatic drugs.
This literature review will evaluate the Pros and Cons of each of these programs, targeting the control of coccidiosis in poultry by reducing the oocyst output and its sporulation, building sufficient immunity in the birds, and sustaining an acceptable production standard. This presentation will help the poultry industry in evaluation of their present control programs, the implementation of the most appropriate control programs by the decision makers on their operations, and to recommend future road map to researchers, in an attempt to better control this persistent coccidiosis disease in the global poultry industry.
The outbreak of coccidiosis in layers result in temporary loss of eggs. The etiology of poultry coccidiosis includes Eimeria acervulina, E. maxima, E.tenella, E. necatrix, E. brunetti, E. mitis and E. praecox. It is worth noting that the inclusion of E. hagani and E. mivati in the etiology of this disease is still under review. The protozoan organisms of coccidiosis are confined to the intestine of poultry, rendering its transmission via the ingestion of sporulated oocytes shed through the droppings. The life cycle of Eimeria spp. is complex, including sexual and asexual stages, with variable pathogenicity of its organisms in different poultry breeds. The intestinal lesions by the Eimeria organisms could range from mild mucosal inflammation to serious villous atrophy, with scores given to such gross lesions between 1 to 4.
Different Coccidiosis control programs
The coccidiosis control in poultry was focused on three areas, including poultry house management, development of vaccines, and use of prophylactic cocidiostatic drugs in feed.
Poultry house management
This oldest control program focused on optimizing the poultry house environment to reduce the infectivity of Eimeria organisms. Documented researches related to impact of poultry house management on coccidiosis showed the following negative environmental factors on this disease namely, a high stocking density in a warm environment, ambient temperature of 25 °C high relative humidity over 60%. These factors will favor the oocysts sporulation and survivability, by which the degree of sporulation determines the level of pathogenicity. It is worth noting that there are factors proven by other researches that can reduce the challenge by Eimeria namely, the bacteria and ammonia in the litter with high moisture content that can damage the oocytes in shorter time. In the normal situations, the oocytes viability in the litter decreases after three to four weeks. Others emphasized the biocontrol and biosecurity for reducing the number of infective oocytes.
Attenuated vs. non-attenuated
The first protection against E. tenella was reported by Beach & Corl in the year 1925. The inclusion of wild type strains in non-attenuated vaccines tend to have a higher oocyst output compared to attenuated products. Live coccidial poultry vaccines contain oocytes of eight or less species of Eimeria. For fifty years, live vaccines were restricted to layers and breeders. The immunity level produced by these vaccines determines the score of gross lesions by the challenge, oocyst output and performance of vaccinated birds. The Coccivac was the first registered non-attenuated vaccine in U.S.A. Consequently, many coccidial vaccines were marketed in the last 20 years.
Subunit and recombinant vaccines
Subunit vaccines include in their preparation the proteins derived from the virulent Eimeria parasite; however, the recombinant vaccines contain proteins that are extracted from sporozoites, merozoites and gametocytes, with a potential of inducing humoral and CMI immunities that are specific to the engineered proteins. It is a necessary condition, for a successful development of these vaccines, to induce protective amount of the acquired immunity in the poultry host. It is worth noting that CoxAbic® is the only marketed recombinant oil-adjuvanted vaccine, developed to protect the broiler progeny.
The delivery of DNA genes to the poultry host is expected to encode proteins that will induce host immunities targeting protection against the field Eimeria spp. The constructed vectors annealed to the specific delivered genes have a purpose of inducing efficient expression of the antigenic proteins of Eimeria.
Prophylactic coccidiostatic drugs
The intensive nature of the present global poultry industry ensures the continuous presence of coccidian organisms, which led to ineffective attempts to eliminate coccidiosis. The oldest treatment of coccidiosis was by Sulfonamide. Later, the sulfonamide was used in prophylactic programs for prevention, by adding it continuously in feed, with lower concentration than that used for treatment. In the same year, sulfaquinoxaline was introduced as a commercial product, by which the age of chemotherapy was initiated. The anticoccidial drugs are classified nowadays into the following groups:
- Synthetic drugs (chemicals), with known or unknown mechanism of
- Polyether (ionophores) with a common mechanism of action, manifested by shifting the ion transport and disturbing osmotic balance in the parasite. Ionophores are products of fermentation of Streptomyces or Actinomadura
- Mixed products such as those in Maxiban, containing nicarbazine and narasin, while Lerbek contains Meticlorpindol and
It is worth noting that the above classes of drugs form the basis of coccidiosis control in poultry, through programs that are still prevalent until today.
Pros and Cons of different control programs
Poultry house management
The Pros are obtained by appropriate biosecurity measures, including efficient disinfectants, aiming at elimination or reducing Oocytes number in the poultry house. Reducing the bird density is proven to decrease the oocytes output, which is rated as the best approach in house management programs.
The Cons are due to difficulty to clean and disinfect hard oocytes on feeders and drinkers. Unfortunately, the favored environmental conditions for chicken production favor the oocytes sporulation (25 °C, and humidity of > 60%). The approach of increasing the litter humidity, targeting to inactivate the oocytes by bacteria and ammonia generation, is not recommended due to expected increase in skin blisters, footpad lesions, and mucosal deciliation by ammonia. Unfortunately, the present requirement for dry litter to improve poultry production will favor sporulation of the Eimeria oocytes.
Attenuated vs. non-attenuated
The Pros in building immunity and protection due to exposure to low counts of non-attenuated oocytes of E. tenella was reported early in literature. The Primary use of vaccines for layers and breeders was successful when strict vaccine management is adopted to avoid failure or severe vaccine reactions. The attenuated vaccines proved to have short life cycle, leading to reduced pathogenicity and higher safety, mainly due to loss of schizogonous stages.
The Cons in attenuated and non-attenuated vaccines is the difficulty in obtaining uniformity of oocyte intake per bird; this is due to uncontrollable number of passages of the oocytes and the density of the oocytes output due to different environmental conditions on the farms. The replication of Eimeria organism is affected by many factors including, excystation, crowdedness, nature of the litter, immune system competitiveness to the different species in the vaccine, and host susceptibility. This leads to uneven replication of the different Eimeria spp. That are put in one vaccine, attenuated or non-attenuated. In addition, the field variants within the same specie could escape the acquired immunity by the administered strains present in the vaccine. Introducing live non-attenuated strains of different Eimeria species in a vaccine to a farm is not acceptable, due to failures that could result in outbreaks due to the vaccine itself. The attenuated vaccines are proven more safe than the non-attenuated ones; however, their induction of enough specific immunity to the prevalent variants on the farms has to be continuously monitored.
Subunit and recombinant vaccines
The Pros in subunit and recombinant vaccines are in their safe technology, targeting the induction of immunity in the host to surface proteins of Eimeria organisms in its different life cycle-stages including, sporozoites, merozoites, and gametocytes.
The Cons in these vaccines is their injectable nature, causing higher labor cost. In addition, the slow process in developing these vaccines, due to the difficulty in reaching a success recombinant vaccine technology for Eimeria control. Accordingly, we can see until now just one available commercial recombinant vaccine in market known as CoxAbic®, with reported 53% protection against E. maxima challenge.
The Pros in DNA-based vaccines is the use of vectored genes that will be delivered to the bird, which undergo a translation process in the host cells generating immunogenic proteins of the Eimeria organism, and by that avoid the maternal immunity that could neutralize the vaccine antigens. Many antigens of Eimeria were tested in such technologies (IMP-1, SO7, ETROH1, p250, EaSC2, Eam. LDH, profiling (3-1E), EtMIC2, MIC4, cSZ-JN1, EtSAG1 (TA4), EtCDPK (pEtK2), and the EtCall), with variable resulting efficiencies.
The Cons in these vaccines is that they can induce immunity against the encoded protein of the vaccine which might not protect against the many species of Eimeria. In addition, the translated protein from the delivered genes might not be enough in quantity to induce a proper level of immunity needed for protection against coccidiosis.
Prophylactic coccidiostatic drugs
The Pros in prophylactic cocidiostatic drugs are significant, which led to a major role in the growth of poultry industry for the last 50 years. This successful approach becomes more productive when the coccidiostats are used in shuttle and rotation programs. However, it is advised to include coccidiostats with different mode of action during the shuttle or rotation programs in order to avoid development of resistance by the Eimeria spp.. The recommended inclusion rate of coccidiostat in the feed should be respected in order to give a static effect on multiplication of Eimeria, and by that allow the immunity to develop to the challenging strains in the field. The correct program of inclusion of coccidiostat will control indirectly the Clostridium perfringens injury to the intestine, and by that avoid the expenses of antimicrobials against this bacterium.
The Cons of prophylactic coccidiostatic drugs is the development of resistance in Eimeria organism. which is difficult to characterize due to the high cost and the unavailability of ‘Anticoccidial Susceptibility Test’ in most countries, especially the developing ones. The other concern is the consumer’s pressure against drug residues in poultry products. Another disadvantage of this approach is the narrow therapeutic index of some anticoccidial drugs (sulfonamides), which is a concern for causing toxicity in the birds. In addition, a toxicity problem could arise even with the use of recommended level of certain coccidiostats in the hot climate, under heat stress (Nicarbazine). Moreover, the ionophores are proven incompatible with some antimicrobials that are used against bacterial infection namely, tiamulin, erythromycin, and some sulfonamides; in addition, lapses with coccidiosis could occur during restricted feeding, long withdrawal periods, ammonia build up in the farm that reduces the feed intake, incorrect inclusion rate in the feed due to non-uniform mixing and dust losses. Last but not least, the use of organic arsenicals (Roxarsone), to improve the efficacy of ionophores, resulted in toxic effect on the birds.
New Global Directive in Avoidance of Residual Coccidial Drug in Poultry Products
Norway is the most strict country in use of coccidiostats. It approved the use of only five coccidiostats in poultry, and all were ionophores. This decision left no place for shuttle or rotation towards a drug with different mode of action. In addition, certain Norwegian studies indicate that the use of narasin is related to antibiotic resistance in bacteria, which brought a new alert to their decision makers. According to FAO, the industrial world has defined legislation and regulations for control of coccidiostat use in poultry, while most developing countries had an absence of these regulations, or failure in policing such regulations (FAO/WHO, 2004).
The search for alternative safe approach in control of coccidiosis
The major Cons for coccidiostat use in poultry, discussed previously, was the resistance to drugs by different Eimeria spp., and the consumers pressure demanding poultry products that are free from residues of drugs. This situation directed research for finding alternative safe approaches. Most of these researches had a common objective of finding herbs that have active ingredients against the multiplication of Eimeria spp. Documented researches related to the following evaluated herbs with anticoccidial properties namely, Artemisinin, Beta vulgaris, Aloe vera, Echinacea species, Azadirachta indica (Neem), Camellia sinensis, Curcuma longa Linn (Curcumin), Origanum vulgare, Saccharum officinarum, and Mushrooms and their extract.
References are available on request
Compiled researches from nine countries (2013-2017) led to an Invention of Comprehensive Natural Control of coccidiosis