*Dr. Wael Abdelrahman is a technical consultant with Biomin Holding GmbH.
COCCIDIA infection (coccidiosis) is a significant endemic disease in poultry that has a considerable economic impact on producer profitability.
The disease is caused by ingestion of the infective oocysts of various species of the protozoan parasite of the genus Eimeria. The annual financial loss to the poultry industry as a result of coccidiosis worldwide has been estimated at around $3 billion due mainly to prophylactic or therapeutic in-feed medications and also as a result of the disease's impact on poultry health (Williams, 1999).
Eimeria species multiply in the bird's intestinal tract, causing considerable tissue damage and, subsequently, impaired nutrient absorption and blood loss. In addition, it can cause diarrhea, dehydration, mortality, a transient drop in egg production in laying flocks and increased susceptibility to other diseases such as necrotic enteritis.
The severity of the infection depends on the number of ingested oocysts and the immune status of the birds; however, the disease is self-limiting.
Chickens are the natural host of seven species of eimeria, with Eimeria tenella, Eimeria maxima and Eimeria acervulina being the most common species. All ages and breeds are susceptible to infection, but outbreaks of coccidiosis usually take place between three and six weeks of age.
Mild infections stimulate the birds' immune system and limit any further infection with the same species because there is no cross-protection between different species of eimeria.
The ubiquitous nature of coccidia makes quarantine or disinfection strategies for successful disease control impossible.
Control of coccidia has been greatly dependent on the use of chemotherapeutic agents. The use of these compounds to control coccidiosis has proved to be successful in many parts of the world due to their ease of use and the ability to provide uniform treatment and prevention.
Nevertheless, these drugs, on some occasions, can be toxic to the birds and also have to be rotated from time to time to minimize the possibility for eimeria species to develop resistance to them.
More recently, the poultry industry has been under pressure to reduce reliance on antimicrobials, including anticoccidial drugs, despite the global acceptance and success of these drugs.
The pressure comes primarily from the high costs of these antimicrobials, which contribute to the cost of disease control, besides public health concerns and demands for drug residue-free products.
Moreover, the development of resistance or decreased sensitivity of eimeria species to chemotherapeutic agents has been reported for several years now from different parts of the world, and this resistance has caused significant reductions in drug effectiveness. Although some coccidia develop less resistance to some drugs, long-term exposure eventually leads to a loss of sensitivity and development of resistance to the drug.
The main strategy to reduce the development of such resistance is to use less-intensive shuttle and rotation programs.
Coccidia vaccines have achieved relative success in controlling the disease, especially in broiler breeders; however, they have not yet achieved satisfactory levels, particularly in broilers as their use is limited by the possibility of adverse effects on feed efficiency and high production costs, especially when these vaccines include more than one eimeria species.
Yet another factor limiting the use of vaccines against coccidia is the inclusion of several species of eimeria in one vaccine, which can cause a further depression in weight gain and feed conversion and a potential vaccine failure.
To facilitate the development of novel control strategies for coccidiosis, it is crucial to gain more knowledge about the interaction between eimeria species and the birds, with a comprehensive understanding of the birds' immune system.
Gut microflora plays an important role in birds' immune system as it is considered one of the first lines of defense against pathogens. Probiotic supplementation of the gut microflora in people and animals has been shown to increase the gut's defensive mechanisms against enteric pathogenic microorganisms.
Probiotics have been studied and used extensively in the poultry industry for their benefits on bird performance, immunity and protection against enteric diseases. However, little is known about their use to control parasitic diseases such as coccidiosis.
Although most studies have focused on the effects of probiotics killing pathogens at the gut level, studies on non-gut pathogens in animals, such as Babesia and Trypanosoma, among others, support a remote effect of probiotics, possibly through a non-specific immune modulation (Cawthorn et al., 1981; Travers et al., 2011).
Few studies have been conducted to look at the effects of different probiotic strains on coccidiosis in poultry, such as Bacillus species, Saccharomyces boulardii, Lactobacillus acidophilus, Lactobacillus salivarius, Lactobacillus reuteri, Pediococcus acidilactici, Enterococcus faecium and Bifidobacterium animalis (Qin et al., 1995; Dalloul et al., 2003a, 2003b and 2005; Tierney et al., 2004; Lee et al., 2007a, 2007b and 2010b; Ghasemi et al., 2010).
Recently, a research group in the School of Veterinary Medicine at Aristotle University of Thessaloniki in Greece evaluated the effect of dietary supplementation of feed with different probiotic preparations given to broilers experimentally challenged with E. tenella sporulated oocysts on day 14 (Giannenas et al., 2012).
The experimental groups consisted of positive and negative controls, a group that was challenged with E. tenella and was given the anticoccidial lasalocid at the level of 60 mg/kg of feed and the remaining groups that were all challenged with E. tenella and were given the basal diet supplemented with different probiotic preparations. These probiotic preparations included E. faecium, B. animalis, L. reuteri, B. subtilis and the multispecies probiotic mix of five poultry-specific strains: E. faecium, P. acidilactici, B. animalis, L. salivarius and L. reuteri (PoultryStar).
The overall performance of birds fed the probiotic blend was significantly higher than the infected control groups, while overall oocyst shedding was significantly lower in the lasalocid-treated group, which also showed significantly lower cecal lesion scores compared to the untreated infected group, but the scores did not differ from the E. faecium, B. animalis and probiotic blend groups. These results suggest that probiotics could be used to reduce the effects of coccidiosis in broilers.
The same research group conducted another experiment to support their previous findings (Giannenas et al., unpublished). They looked at the effect of the probiotic blend on the performance and gut health of broilers experimentally challenged with coccidia (E. acervulina, E. maxima and E. tenella sporulated oocysts). The five experimental groups consisted of positive and negative controls, two groups challenged with mixed eimeria species that were given the probiotic blend in feed and a final group challenged with mixed eimeria species that were treated with lasalocid at 75 mg/kg.
The results of this study supported the previous trial and showed that the probiotic blend supplementation exerted an anticoccidial effect against Eimeria species, reflected in the birds' performance, which was similar to those on the lasalocid treatment. Groups fed the probiotic blend showed lower numbers of oocysts shedding, lesion scores and bloody feces than the infected control group but higher numbers than the lasalocid group.
Also, probiotic blend-treated groups had the highest values of villous height and villous height-to-crypt depth ratios in comparison to all other groups.
The combined use of probiotics and coccidial vaccines and the effect on birds' immune response was studied by another research group in the U.S. (Stringfellow et al., 2011). The experiment consisted of four groups: a negative control, a probiotic blend treatment, vaccinated and probiotic blend plus vaccinated groups (Figure 1). The probiotic blend was administered in drinking water at an inclusion rate of 20 g per 1,000 birds per day, while birds in the vaccinated groups received Coccivac-B on day of hatch.
The researchers looked at the immune modulatory effects of the probiotic mix and the vaccine used on the innate and adaptive immunity. Positive immune modulatory effects were shown in the group that received the probiotic blend and vaccine on days 14 and 21 compared with all other groups (Figure 2).
The results of this study highlight the fact that the addition of probiotics in the drinking water of coccidia-vaccinated broilers may offer increased protection at vaccination time or an adjuvant effect by immunomodulation of the birds' immune system. This provides an opportunity to improve currently existing coccidia vaccines.
Nevertheless, vaccines are still the most powerful solution for controlling coccidiosis in poultry and reducing its negative economic impact. However, until these vaccines are available for commercial use, the industry has to consider other alternatives, such as probiotics, that can be used with anticoccidial drugs.
With current knowledge and advances in direct-fed microbials, proposing probiotics as an alternative to conventional chemotherapeutics to control coccidiosis seems impractical. However, it can be used as a complementary approach in shuttle and rotation programs to reduce the incidence and severity of the disease as well as the development of anticoccidial drug resistance in eimeria species.
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