The cellular and molecular mechanisms leading to immune protection against coccidiosis in chickens are complex and include multiple aspects of innate and adaptive immunity. Innate immunity is mediated by subpopulations of immune cells that recognize pathogen-associated molecular patterns. Adaptive immunity, which is important in conferring protection against secondary infections, involves subtypes of T and B lymphocytes that mediate antigen specific immune response. Experimental studies in coccidiosis in chickens now support the role of lymphocytes and their secreted products (Lillehoj et al. 2011)
Eimeria parasites have a long and complex biological cycle with exogenous and endogenous phases that trigger the immune system of the host. These parasites that cause coccidiosis in chickens can produce substances (chemokines) than can inhibit the immune response.
In the fight against infectious diseases, the first step is the correct identification of the causative agent, and the symptoms and lesions that it causes in the host. A correct diagnosis influences on the effectiveness of the treatment established, particularly if it is combined with preventive measures such as vaccination. Traditional techniques such as microscopic observation and oocysts counting remain very useful as screening methods, and an aid in the diagnosis and treatment of coccidiosis in animals. DNA-based methods such as PCR have overcome some limitations of these conventional methods, allowing the analysis of more samples in less time, increasing sensitivity and allowing the quantification of the parasite in one step.
These new methods positively influence the treatment of coccidiosis, expanding the possibilities for the poultry veterinarian to control the disease.
From the very beginnings of this type of animal production, control of digestive diseases in the poultry industry has been one of the most significant health challenges. Moreover, among digestive diseases, coccidiosis in poultry continues to pose a challenge for the poultry farming worldwide. The incorporation of new tools provides new resources for safe and effective control.
Where are we coming from?
The housing conditions of birds used in production constitute a trigger factor for digestive diseases, with coccidiosis in poultry being one of the most prevalent, caused by parasites of the Eimeria genus.
Eimeria spp is a protozoan parasite with a complex life cycle and so is the host immune response to Eimeria infection. In the last decade, huge progress has been made in the identification of host and parasite genes involved in immunogenicity but there are still some immunity mechanisms to be discovered.
As a general rule, we say that Eimeria immunity is species-specific, meaning that each species of Eimeria is able to stimulate protective immunity against itself. Although some studies suggest that partial cross-protection can be achieved (Augustine et al. 1991), from a practical perspective we have to assume the widely accepted belief that there is no cross-protection between species.
Proper oocyst distribution is a key point for the success of spray application of a coccidia vaccine. Generally speaking, a coccidia vaccine is a suspension of sporulated oocysts in a PBS solution. Because of this fact and because of the characteristics of the oocysts, there are some differences to a common viral freeze-dried vaccine that must be taken into account during the vaccination process.
There are several methods by which coccidia vaccines can be applied, but probably the most convenient, consistent, reliable and accurate way is via coarse spray in the hatchery. Spraying the vaccine directly on to the feed risks desiccating the oocysts and that is one of the few weak points of oocysts.
Uniform ingestion of coccidiosis vaccines made of attenuated sporulated oocysts is of paramount importance for the correct intake of these vaccines and subsequent onset of immunity and has to take place soon after the vaccine is coarse sprayed over the chicks. In order to achieve this, we need to enhance the pecking and preening behaviour of the chicks with the help of a colour and an aroma.
The application of vaccines via coarse spray was conceived mainly for the oral administration of coccidiosis vaccines made of sporulated oocysts.
Avian coccidiosis is a common protozoal gastrointestinal parasitosis caused by the Eimeria species resulting in considerable economic losses in the poultry industry, especially in long life-cycle birds such as layers and breeders. In these high value birds, Eimeria species infection results in clinical or subclinical coccidiosis associated with increased mortality, decreased flock uniformity and a general rise in secondary pathologies subsequent to intestinal damage. Without any doubt, the best known and most widely diagnosed species is Eimeria tenella.
Microscopic picture of the five Eimeria species included in EVALON®: Eimeria acervulina, Eimeria brunetti, Eimeria maxima,Eimerianecatrix and Eimeriatenella.
Chickens are susceptible to seven Eimeria species, the most common species affecting long-life birds being Eimeriatenella, Eimeria necatrix, Eimeria brunetti, Eimeria acervulina and Eimeria maxima.
When we think about the prevention of coccidiosis in chickens raised for a long cycle (breeders and layers) we cannot imagine any treatment other than vaccines. Apart from cost considerations, the use of coccidiostats has been always a handicap in birds that usually have restrictions on feed consumption. This is the reason why the protection conferred by a vaccine applied in the first days of life should be high enough to give a level of immunity that is able to protect them throughout the cycle.
Lesion scores of mid-intestine at 6 days post-challenge with E. necatrix. Lesion scoring grading 0-4 according to Johnson and Reid, 1970. Control vs EVALON® + HIPRAMUNE®T.
Layers and breeders have a production cycle of not less than 60 weeks in most cases. One of the main characteristics of these birds is that the rearing period in a normal poultry house is different to that in a production house.
In the world of livestock farming and animal protein production, the poultry industry has always been the sector with the greatest focus on achieving maximum control and information when it comes to the management of the production process and of the system for monitoring the medicinal products used in this process. HIPRA is going one step further along this path by offering a new vaccination concept, Smart vaccination, designed to provide improved vaccination monitoring and traceability for the prevention of coccidiosis in poultry.
From the early days of animal production, poultry farming has been in the vanguard of technology, feeding systems, farm automation, etc. Poultry production is one of the most advanced and streamlined of all the animal production sectors, guaranteeing all the quality standards demanded by the consumer in each market. A paradox exists, however: the processes associated with vaccination, unlike other parameters such as feeding, environmental conditions, etc., are beyond control.
With the currently increasing problems of drug-resistance and pressures from consumers to ban drugs from animal feeds, there is a pressing need to move away from chemotherapeutic control of coccidiosis towards vaccination. Most commercially available coccidiosis vaccines contain live oocysts of non-attenuated or attenuated strains of different Eimeria species, with the attenuated commercial vaccines produced using different attenuation methods.
The following video explains the process of attenuation of vaccine strains by precociousness:
As the world’s poultry production continues to grow, so do concerns about the control of Eimeria infections that cause coccidiosis, which remains one of the most commonly reported diseases of chickens. The ubiquity of chicken Eimeria precludes eradication so the key role in control of the disease is played by hygiene, anticoccidial drugs and vaccines.