Tag Archives: Coccidiosis in poultry

Vaccines are not dosed in the same way as antibiotics. This concept is even more relevant for vaccines against coccidiosis in poultry

A vaccine dose does not depend on body weight: the mechanism of action of vaccines is different to that of antibiotics and, as a result, the dose does not depend on the body weight of the target animal. When considering vaccines against coccidiosis in poultry, the dose is made up of a suspension of sporulated oocysts of different species of Eimeria.

In this suspension, the oocysts are not evenly distributed unless it is mixed thoroughly. If, in addition to this, the dose is reduced, the chance that the chicks will receive all the oocysts of every species decreases exponentially.
A vaccine does not have to be distributed throughout the body and the vaccine components (antigen and adjuvant) do not act directly on the pathogen. In general, the activity of vaccines starts with a rapid and local innate response depending on the route of administration.

Usually vaccines against coccidiosis in poultry are administered orally, thus the first innate immune response takes place in the gut. As a result of this first phase, antigen-presenting cells are activated (dendritic cells and/or macrophages) that are responsible for processing the antigen and carrying it to Peyer patches where they activate specific T lymphocytes, thereby starting the acquired immune response. As Eimeria is an intracellular parasite, the acquired immunity needed is of the cellular type. In this second phase, effector T cells are generated that produce cytokines ensuring a concentration in the tissues that is independent of the age/weight of the animal for the same dose of vaccine.
Does the same thing happen with human vaccines?
In human medicine, the vaccines that are used in children (paediatric vaccines) and in adults are the same and are used in the same dose. It would not occur to anyone to reduce a vaccine dose for children because of the risk of inadequate protection that this would entail. There are examples of toxoids (tetanus), inactivated vaccines (rabies) and live vaccines (varicella) where the dose is the same for children as for adults.
How is a vaccine dose determined?
The dose that is indicated in the leaflet for each vaccine is the one that has been shown to be effective during the different research phases in the target animal species and with the minimum age that can be vaccinated. On the basis of these studies, the health authorities in each country recommend the specified dose for each product. For this reason, the dose should be administered irrespective of the age of the animal.
There are some older products that have different doses for different age groups, but this would not be allowed nowadays.
What harm can be done by a dose that is lower than the recommended one?
Administration of a vaccine dose that is lower than the recommended one can result in a lower immune response, compromising the protection of the individual against the pathogen. Specifically, with vaccines against coccidiosis in poultry, if a full dose is not administered, there is a very strong possibility that there will be an uneven administration of both oocysts and Eimeria species amongst the vaccinated animals with a consequent lack of onset of immunity in some of the chicks.

Dealing with coccidiosis by reducing the use of antibiotics: is it sustainable? (Part 2)

It is our responsibility to search for and choose the right tools to deal with coccidiosis in poultry with current consumer preferences tending towards the purchase of products from livestock grown using sustainable methods.

Because of worldwide concern about drug resistance associated with the immoderate use of antibiotics in poultry production, there has been a major effort to find alternative treatment and methods of prevention.

There is a greater demand for products from sustainable livestock and the higher prices may encourage the farmer. All these factors are in addition to the strongly held beliefs of many consumers that broilers reared with less antibiotic use not only provide additional health benefits to them and their families, but also that sustainable farming practices provide long-term environmental benefits.

It is well known that the major use of antibiotics in poultry farming is linked to coccidiosis prevention and treatment. Therefore, this is the starting point for thinking about reducing their use.

First of all, a biosecurity program needs to be implemented and well managed. It is an everyday goal. The program should address points such as controlling access by individuals, cleaning and disinfection, feed and water quality, access by other animals.

The second step is to study the available alternatives for dealing with coccidiosis. Researchers like Niewold in 2007 have suggested that the unique and highly reproducible effects of in-feed antibiotics may be due to the prevention of immunological stress or their anti-inflammatory effect rather than their antimicrobial role, and this should be considered when searching for new compounds to be used as replacements.

Since we know that prevention it is a key point in sustainable animal farming, vaccination is an important tool to be considered.

Over the past 10 years, experiences in the field have provided data regarding this cost/benefit ratio, derived from the use of rotation programs with precocious attenuated vaccines, such as HIPRACOX®.

Rotation programs allow the poultry farmer to decide on the use of fewer preventive antibiotics – anticoccidials – and to decrease coccidiosis lesions, which means less use of antibiotics as treatment.

This is a long term plan, in which every decision must be taken in a responsible way. Using the right tools, success can be achieved in the matter of coccidiosis with the use of sustainable methods.

Niewold T.A. 2007. The nonantibiotic anti-inflammatory effect of antimicrobial growth promoters, the real mode of action? A hypothesis. Poultry Science, vol. 86 (4), 605-609.

Dealing with coccidiosis by reducing the use of antibiotics: is it sustainable? (Part I)

One of the most worrying problems in poultry production is coccidiosis and how to deal with it without using antibiotics. It is a challenge that, we know, lies in prevention. Furthermore, it is impossible to think in terms of prevention and not to link this to sustainable action.

Thinking sustainably is to link the human population, animals and the environment into every decision or action. It is believing that the world is entirely interconnected.

The concept of One Health was envisaged and implemented by the OIE in the early 2000s as a collaborative global approach to understanding the risks to human and animal health and ecosystem health as a whole, and has everything to do with sustainable action.
Global sustainability affects veterinary medicine on a significant scale, and it is a particular challenge. Since the veterinary professionals play key roles in different parts of the ecosystem, it is necessary for them to understand what is happening in almost every other area of knowledge. Moreover, veterinary medicine is the only profession that routinely operates at the interface of these three components of One Health.
It is important to say that sustainable ways of thinking also look at economic aspects, which are needed for efficient production.
With regard to the poultry industry, it is impossible to make any decision without taking into account the health aspect. Every management plan looks first at the birds’ health because it is something that is influenced by every factor on a farm: buildings, nutrition, welfare.
The importance of digestive diseases is well known and, amongst these, coccidiosis can be named as one of the major health problems, and how to deal with it has been widely discussed during recent years. However, nowadays, there is a great deal of concern about the use of antibiotics in the poultry industry. The widespread use of anticoccidials or antibiotics has led to a resistance problem, which means that many of these drugs are no longer effective. One approach to be considered is to decrease antibiotic usage so that fewer numbers of bacteria are exposed to antibiotics and fewer resistant genes develop. Unnecessary use of antibiotics has been identified, and government associations are recommending a reduction in their usage (e.g. White House, 2015. National Action Plan for Combating Antibiotic-resistant Bacteria Washington, DC pp. 1–62).
Keeping the sustainability aspect in mind, it is to be recommended that poultry farming should focus on prevention rather than treatment. Indeed, in veterinary medicine, prevention and sustainability could be synonymous.
The prevention of coccidiosis without the use of anticoccidials or antibiotics is now a reality for forward-looking farms. There is increasing awareness amongst consumers about the products they purchase. They want to know how the animal was raised and processed, besides what sustainable practices were applied during the process chain.
It is a win-win situation: famers guarantee a standard of flock health, consumers purchase sustainable products.

Key points in the diagnosis of coccidiosis (Part 2: Lesion Scoring)

When decisions concerning the prevention or control of coccidiosis in poultry are based on the subjective scoring of macroscopic lesions, observed in the gut of a number of birds in a flock, several factors affecting the method should be considered. Proper selection of birds, a careful sampling procedure and sample handling along with an accurate judgment of lesions, are some of the most important methodological indicators for success in lesion scoring during a flock inspection.

1. Selection of the right birds in the right number:

Before necropsy, it is essential to check the history of vaccinations, treatments (anticoccidials in particular) and previous diagnoses of the flock to be sampled. It has been shown that the existence of gut lesions is not necessarily accompanied by clinical signs of coccidiosis in poultry (Williams et al., 2000).
In fact, the score that has been used for decades was developed in naive birds (Johnson et al., 1970). However, it has been shown that immunized birds may display lesions and high oocyst counts, with no growth retardation or clinically overt disease. In these cases the lesions are of no economic significance.
As for the number of birds to be examined, it is necessary to seek the right balance between the need to evaluate a representative sample of the batch of birds, and the willingness of the farmer to provide enough birds. Generally, a total of 5 to10 broilers, 25-35-days old, from each house would be reasonable. These birds should be of the average weight of the batch, and be alive at the time of sampling, not debilitated or fasted.
2. Sampling:
As previously mentioned, it is crucial that birds examined for gross lesions (at least 5 per batch), are alive and within the appropriate age range. If multiple groups are inspected, it is better to sacrifice one group and then another to reduce post-mortem artifacts. It is equally important that, as far as possible, the inspections are always carried out by the same person who evaluates the different batches of birds coming from the same farm. This is mainly because their experience enables them to reduce the variation inherent in the scoring system.
The intestine is the first organ to decompose after death. Postmortem changes negatively influence the assessment of pathological changes in the gut. Make the sacrifice humanely with the least possible stress. The preferred euthanasia method on the farm is generally cervical dislocation. This should be carried out by trained staff because if not done quickly and effectively, it can inflict pain and distress. Sacrifice by carbon dioxide inhalation is another valid alternative, if it is available.
3. Sample handling:
To complete the inspection in a systematic way, consider the four segments of the intestine that are shown in Figure 1. Do not expose the inner surface of the intestine until you have inspected the outer wall. It is important to record any change in thickness, colour or presence of spots that may be indicative of injury.
Expose the inside of the digestive system including the gizzard, proventriculus and cloaca. Do it using a different scissors and forceps kit for each group of animals. Observe and describe the content found (amount and appearance), as well as any other signs that catches your attention. Inflammation of the intestine can sometimes be identified immediately after cutting the wall longitudinally, as it tends to fall back on itself.
This only happens when it belongs to a bird that has been recently sacrificed. List all the lesions observed, their exact location, colour, appearance, distribution, shape, etc. Whenever possible, take photos of the lesions found.

There are seven Eimeria species that are responsible for avian coccidiosis, 5 of which cause the disease in broilers: E. acervulina, E. mitis, E. tenella, E. maxima and E. praecox.

Finally, close collaboration between the veterinarian and the farm staff is crucial to avoid possible biases of the method, or the over-interpretation of the lesions found. The availability of detailed information on health management of the flock, and the right amount of suitable birds for inspection will be very important, before making decisions on the control of coccidiosis based on the results of inspections and lesion scoring.

Key points in the diagnosis of coccidiosis (Part 1: Identifying and counting oocysts)

The prerequisite for the control and treatment of coccidiosis in poultry is to correctly identify the presence of disease. Two of the most widely used methods for this purpose are the identification and enumeration of oocysts, and the identification of lesions in the intestine. Although egg identification and counting was described for decades, and has been used since then, it is important to consider some key aspects of the method to obtain valid results.

1) Be familiar with the morphology of the parasite:

Have skills to identify the Eimeria species is the main element to be considered for the success of the morphometric study of field samples. For this, it is convenient to train yourself using pure parasite suspensions obtained in the laboratory.
Although field samples differ greatly from these suspensions (Figure 1), particularly as regards the debris and impurities contained, if they are well preserved (refrigeration at 4-8ºC) the typical morphology of each Eimeria species is easily recognizable.Once familiar with the microscopic appearance, experience after analyzing many samples is what allows you to refine the method, always with an error range due to the “atypical” forms that can be found in all field samples.
2) Use only samples in good condition:
Counting and identification of oocysts, like any other diagnostic method, requires samples to be preserved in good condition. There is, however, a trend to believe that Eimeria oocysts are “indestructible”.
Whilst these parasitic forms are among the most resistant known, their shape can be altered if the oocyst ages or matures (sporulates) over time, particularly when the temperature and humidity are favorable. To avoid this disadvantage, it is very important that the samples are fresh (preferably <7 days after being collected) and remain stored under refrigeration until they are analyzed.Thus maturation is prevented and the number of atypical forms is reduced.
3) Place your confidence in a certified laboratory that provides a guarantee:
Not all laboratories perform the identification and counting of Eimeria oocysts in exactly the same way. However, there are some requirements that must always be met, if valid, repeatable and accurate results are expected. The validity is mainly linked to the prevention of cross-contamination among samples. The possibility of getting false positive results by cross-contamination in the laboratory is very high, particularly in places with a high workload. Thus, practices such as using disposable and sterile materials, changing gloves between critical steps in the procedure, etc., are crucial.
On the other hand, the robustness and accuracy depend very much on the use of calibrated instruments and validated methods. Some key points are the correct homogenization of the sample before processing, weighing accuracy, the use of the correct dilution factor, and a microscopic observation method without artifacts.
Finally, before making decisions about the treatment of coccidiosis based on the laboratory results, it is important to consider that Eimeria is prevalent and is found in the faeces and intestines of poultry.
Therefore the significance of this finding must be weighed against other indicators of disease, such as the presence of clinical signs in live animals, as well as macro lesions and microscopic lesions in the intestine.

Is it possible to rear broilers without antibiotics? First step to achieve the goal: vaccination against coccidiosis in chickens

Prevention of coccidiosis in chickens with live vaccines means suspending the use of anticoccidials, but a reduction in other antibiotics has also been observed. Reduction in antibiotic use in animal production is currently one of the aims of the poultry industry. Antimicrobial resistance has become a global public health problem in humans and livestock and plans to reduce the use of antibiotics are being implemented by the authorities in most countries.

Obviously, chemicals and ionophores used to control coccidiosis should be considered as antibiotics because the parasites that are intended to be controlled with these products can develop resistance with prolonged use of these substances.

Vaccination against coccidiosis in chickens has an indirect effect on gut-related diseases (dysbacteriosis, necrotic enteritis, septicaemia after gut leakage) and the consumption of antibiotics could therefore be altered.
It has already been seen that the implementation of a coccidiosis vaccine (HIPRACOX®) in a rotation programme yields a significant improvement in zootechnical results (Ronsmans et al. 2015a). Hipra, in collaboration with the poultry practice Galluvet in Belgium (Ronsmans et al. 2015b), has conducted a study to determine whether vaccination with HIPRACOX® affected the use of antibiotics in broilers. The hypothesis was that if intestinal health was enhanced, the overall health of broiler farms would improve.
In the trial, the effect of the administration of HIPRACOX® on the use of antibiotics on 21 farms in Belgian field conditions was studied. The trial was conducted on the premise of the benefits of rotational programmes but we realised that the use of the vaccine could have a positive effect on reduced antibiotic use during the rearing period.
Some of the farms had a background of coccidiosis problems. Under these circumstances, the use of a coccidiosis vaccine offered adequate protection and there was a clear and significant reduction of treatments against coccidiosis in chickens. As we can see in Graphs 1 and 2, the number of days of treatment fell by 79.56% during the vaccination and by 51.38% after the vaccination cycles (see image above).
However, more significant still is the fall in the administration of gastrointestinal treatments during the period of use of HIPRACOX®. We evaluated the consumption of molecules used to improve intestinal pathologies (Tylvalosin, Linco-Spectin, Tylosin, Penicillin and Amoxicillin).
The graphs below show the evolution of their use on the farms before the administration of HIPRACOX®, during administration of the vaccine and after. The days of treatment per cycle fell by 16.4% during vaccination and by 45.24% after vaccination. Moreover, the amount of active molecule per kg of average weight decreased by 17.39% during and 30.4% after vaccination.

Popular belief tells us that more cases of necrotic enteritis and dysbacteriosis appear in vaccinated flocks due to the lack of the anticlostridial effect of the ionophores. However, no cases of necrotic enteritis were seen during the trial. Furthermore, the quantity of antibiotics used for enteric diseases fell in the period in which the vaccine was used. These observations are consistent with the review conducted by Williams (2005).

Once again, prevention in broiler production is key. A good vaccination programme including vaccines against coccidiosis in chickens could be the best option for those producers that are considering reducing or even phasing out the use of antibiotics on rearing broilers.
In conclusion, the first aim of a coccidiosis vaccine is to prevent coccidiosis in chickens but an indirect effect of coccidiosis vaccine on other diseases can be expected, probably due to an improvement in intestinal integrity.

Can Eimeria vaccines replace anticoccidials for the prevention of coccidiosis in poultry farming?

Coccidiosis – due to parasites of the genus Eimeria – is one of the most devastating diseases in poultry: a disease which has always being present in every poultry flock since the first chick appeared on the earth; in fact, Eimeria is an ever-present parasite that it is impossible to eradicate. For this reason, a coccidiosis prevention strategy needs to be put in place for each batch of chickens that arrives on a farm. Worldwide losses due to coccidiosis in poultry are estimated to be around US$1.5 billion/year.

From the 1950s the use of some chemical molecules has been implemented to prevent the effects of the several Eimeria species that cause the disease. Whereas the use of vaccines is quite commune in breeders, only between 5 and 6% of broilers in the world are actually vaccinated instead of being treated with anticoccidials.

The prevention of coccidiosis in poultry with some Eimeria vaccines is absolutely safe and efficacious as also demonstrated recently by Alameda et al. 2015 and Ronsmans et al. 2015. So the question is, why is the prevention of coccidiosis with the vaccines available not more widely used around the world? In this post I will try to answer this question from several perspectives.
The first important question to answer is whether or not it is possible. The answer is clearly yes it is. The entire production of breeders, free-range or organic chickens and a percentage of the industrial production of broilers are produced today without the use of anticoccidials. So, the first thing to take into account is the willingness of broiler producers to do it.
The second question is the cost. Some people think that vaccines are more expensive than anticoccidials, but this is not always true. It depends on the duration of fattening of the broiler, the anticoccidial programme used and, of course, on the quality of the final broiler produced, whether or not it is free of anticoccidials.
The third question is management. Some producers think that the use of anticoccidials in the feed is much simpler than vaccination. But it is not well known that the use of anticoccidials in the feed could potentially lead to cross-contamination in the feed mill, especially when the plant produces feed for more than one animal species. This could be the case with salinomycin in turkeys: salinomycin is one ionophore widely used in broiler feed as an anticoccidial, whereas it is well known that it is very toxic for turkeys, even at levels lower than therapeutic ones (Potter et al. 1986). Moreover, it has to be recalled that nowadays the administration of Eimeria vaccines is becoming more and more practical and standardised as most of the applications – especially for broilers – are performed in the hatchery with spraying devices that have been designed for this specific use, like Hipraspray®.
Finally, there is another important question to answer which is whether the availability of vaccines would be sufficient to replace anticoccidials completely. The answer to this question is not easy. Of course companies producing Eimeria vaccines do not produce sufficient quantities at present, because there is no need for it. However, if broiler production in the world started to demand Eimeria vaccines, there’s no reason to think that given time, the companies would not have a sufficient amount of vaccines available.
Eimeria vaccines have a short shelf-life, so they have to be manufactured in response to demand because they cannot be stored for more than a few months. But, again, this is not a very important problem due to the fact that the modern poultry production system is so industrialized that vaccinations can be planned easily and with a long notice period. For this reason, the production of vaccines can be easily planned and in the most accurate way.

Coccidiosis in chickens: the role of subclinical species of Eimeria

The fight against coccidiosis in chickens means the adoption of different strategies depending of the type of bird. If we are managing long life cycle birds, we have to pay special attention to clinical Eimeria species that are able to generate a real coccidiosis process with macroscopic lesions and symptoms that will reduce the healthy status of the birds and will compromise the development of immunity against other diseases or cause the death of the birds.

However, when we are rearing standard, certified or even free-range broilers, the focus needs to be a different one. In these cases it will be difficult to find real clinical coccidiosis. Otherwise, the “silent” species – such as Eimeria praecox among others – will affect the intestinal mucosa and will reduce the capacity of a broiler for nutrient absorption. Dealing with subclinical species is essential in coccidiosis in chickens with a high growth rate.

For a long time, there was a trend to classify coccidiosis in chickens according to the age of the birds. It was considered that E. acervulina, E. maxima and E. tenella were species affecting all the birds. In the case of long life cycle birds such as breeders and layers, it was necessary to include E. necatrix and E. brunetti in the composition of vaccines against coccidiosis. Indeed, this is true for long life cycle birds because feed conversion and growth is important, but not the key point. In fact, these birds are reared under feed restriction.

The chicken intestine has a very important part that plays a main role in digestion and absorption of nutrients. This is the duodenum.
The duodenum is a part of the small intestine where the main digestive processes occur. The pancreas will provide digestive juices into the duodenum for protein digestion in particular and the liver (via the gall bladder) will produce the bile, a gastric juice involved in the digestion of lipids and absorption of vitamins A, D, E and K. When we are treating coccidiosis in chickens –and more specifically in fattening broilers- it is essential to identify the species of Eimeria located in this part of the intestine.
E. acervulina, one of the most prevalent species in broilers, prefers this part of the intestine even if the level of infection is moderate. It is quite typical to find the white ladder-like spot lesions scattered and confined to the duodenum:

E. praecox is also located in the duodenum. For a long time, E. praecox was considered to be a non-pathogenic strain. After the studies by Williams et al. (2009), the pathogenicity of E. praecox was demonstrated. There are two facts to consider with regard to the damage caused by E. praecox in coccidiosis in chickens:

On the one hand, praecox causes microscopic damage in the cells of the duodenum. In infections with E. praecox oocysts (106) it is possible to see villus atrophy, crypt hyperplasia and increased leukocyte infiltration.
On the other hand, praecox modifies the viscosity of the liquids in the duodenum. In infections with E. praecox an increase in whitish mucus and non-digested feed is observed.

Finally, in other studies carried out by Répétant et al. 2011, the impact of the infection caused by E. praecox was related to the infective dose but its impact on performance was present from the lowest dose of 5,000 oocysts/bird when it was co-administered with E. acervulina.

After all these arguments it seems of great importance to include Eimeria praecox as a target in the fight against coccidiosis in chickens in fattening birds where the integrity of the duodenum is a must. This is the reason why in the design of the composition of HIPRACOX® it was decided to include E. praecox together with E. mitis to protect against the effects of subclinical coccidiosis in chickens.

The Eimeria species responsible for coccidiosis in broiler chickens

The Eimeria species responsible for coccidiosis in the species Gallus gallus are: E. acervulina, E. maxima, E. mitis, E. praecox and E. tenella, which are responsible for the disease in short life-cycle poultry (broilers), and E. necatrix and E. brunetti, which, together with the above 5 species, are responsible for the occurrence of outbreaks in long life-cycle poultry (breeders and layers). They are all ubiquitous in their behaviour and vary in their pathogenicity.

There are seven Eimeria species that are responsible for avian coccidiosis, 5 of which cause the disease in broilers: E. acervulina, E. mitis, E. tenella, E. maxima and E. praecox.

There are two more strains of Eimeria that are not recognised as causing the disease. These are: E. hagani, the only description of which was by Levine P.P. in 1938; and E. mivati, a species found in a vaccine in the USA which appears to be a mixture of other Eimeria, E. mitis and E. acervulina (M. W. Shirley et al. 1983).
Focussing on the species that are really important in the generation of the disease in broilers, we need to know exactly which species cause most damage and how they interact by generating synergies between one another, thereby causing greater damage within the host. E. acervulina, E. maxima, E. tenella, E. mitis and E. praecox are the main species that cause avian coccidiosis in broilers. They can all be found along the intestine of poultry, affecting different areas and causing different lesions depending on the species concerned.
Focussing on E. acervulina, E. maxima, E. tenella, E. mitis and E. praecox, the species that are responsible for avian coccidiosis in broilers, we need to know the lesions they cause and their behaviour and distribution within the gastrointestinal tract of chickens. Below is a video giving details of the different species of Eimeria that affect the gastrointestinal tract of poultry.
For the development of vaccine strains, the Eimeria species have to be attenuated. There are three methods of doing this: passage through embryonated eggs, gamma irradiation and selection for precociousness. When they are selected by passage through embryonated eggs and by gamma irradiation, this is generally associated with a loss of immunity by the line and therefore stable attenuation is not maintained (Shirley M.W et al. 1984). The best method shown so far is selection for precociousness developed by Jeffers (1975). during the nineteen seventies. The method is based primarily on the reduction of the reproductive potential of the strain, resulting in attenuation of the virulence, maintenance of the immunogenicity and genetically controlled stability.
When the appropriate method of attenuating the Eimeria species has been identified, we need to know which species will be necessary for development of the vaccine. E. acervulina, E. maxima and E. tenella are well known as the pathogens responsible for the disease and are included in the great majority of existing commercial vaccines, but this is not the case with E. mitis and E. praecox, which have been regarded as species of “less importance” in the field.
In his study on the pathogenesis of Eimeria praecox in broilers, R.B. Williams et al. (2009) demonstrated the importance of E. praecox as a pathogenic strain in itself. In this study, it was compared with E. acervulina and it was observed that the lesions caused by E. acervulina were macroscopic and severe, but did not last for more than 14 days post-infection. In contrast, in the case of E. praecox, the lesions were microscopic and caused a reduction in the viscosity of the intestinal content. In other studies such as those carried out by J.M. Répérant et al. 2011, the impact of the infection caused by E. praecox was related to the infective dose but its impact in performances was present from the lowest dose of 5000 oocysts/bird. When it was co-administered with E. acervulina, it caused a greater impact on production indices.
Furthermore, the selection of strains within an Eimeria species is essential in order to obtain good protection, thus conferring cross-protection within each species, as is the case with the vaccine strain E. maxima 013, which is able to provide protection against 6 different pathogenic strains of E. maxima obtained from different geographic locations.
It is essential to find out about the epidemiological behaviour of the Eimeria oocysts in order to understand how the vaccine strains will behave and what vaccine load will be necessary in order to produce an appropriate vaccine response. Generally, the oocysts that are found in the bedding can persist for up to 3 weeks (Williams R.B. 1995), with sporulation being better with a moisture content of the litter from 31 to 62.1%. Whether or not they are sporulated, 20% are ingested by the chickens and pass through their intestines. As immunity is generated within the flock, the percentage of oocysts eliminated is reduced with each life cycle of the parasite. Hence the necessity of determining accurately the volume of oocysts necessary for each vaccine strain, in order to ensure an appropriate response to the vaccine.
In order to confer immunity against all the Eimeria species that are present in the environment, all the Eimeria vaccine strains need to be included as there is no cross-protection between the different species, hence the necessity of formulating a vaccine with the 5 Eimeria species when the target category is represented by broilers.
With all this tested knowledge, HIPRA, a specialist in avian coccidiosis, has developed the HIPRACOX® vaccine, the only vaccine specially developed for short life-cycle poultry, containing in its formulation all the Eimeria species responsible for avian coccidiosis in broiler chickens.

Eimeria tenella is probably the most diagnosed Eimeria on the planet, but what is the prevalence of the other Eimeria species that cause coccidiosis in poultry?

Eimeria tenella is by far the most widely detected species on farms when routine lesion scoring is performed. However, it is well known that Eimeria infections very seldom occur with one single species of Eimeria, most of the time they are multiple. Let’s investigate what are the most prevalent species and how multiple infections usually occur.

As Eimeria tenella is probably the easiest species to detect by lesion scoring, a common belief is that this species is the most prevalent all over the globe. In fact, macroscopic lesions are amongst the most pathognomonic with blood or typical moulds in the caecum and common finding of bloody droppings in the litter.

There are seven species of Eimeria recognized as parasitizing chickens (Gallus gallus), which vary in their ability to induce diarrhoea, morbidity and mortality (Williams 1998). They are Eimeria tenella, Eimeria acervulina, Eimeria brunetti, Eimeria maxima, Eimeria mitis, Eimeria necatrix and Eimeria praecox. They occur throughout the world wherever commercial broilers are reared. All seven species of Eimeria infecting chickens were detected in surveys of commercial poultry farms in many countries, for example, the Czech Republic (Kučera 1990), France (Williams et al. 1996), Sweden (Thebo et al. 1998), the UK (Eckert et al. 1995), Argentina (Mcdougald et al. 1997; Mattiello et al. 2000), Australia (Jorgensen et al. 1997; Morris et al. 2007), China (Sun et al. 2009), India (Aarthi et al. 2010), South Korea (Lee et al. 2010) and Brazil (Moraes et al. 2015).
Like Eimeria tenella that is localized in the caecum, the different Eimeria species tend to develop in different parts of the chicken gut and may be identified by the nature and location of the lesions they cause during multiplication (Long et al. 1976, Long et al. 1982). However, a definitive diagnosis requires additional laboratory investigations. Nowadays, polymerase chain reaction (PCR) and morphometric identification of the Eimeria species are frequently used together as a means of differentiation in the field samples of faeces and litter.
In Europe, few field surveys of Eimeria species are available and even fewer have been conducted using samples from broiler farms. In a study conducted by HIPRA (Pagès et al. 2015), litter samples obtained from broiler farms between 2003 and 2008 in Spain, Belgium, Italy and France were evaluated for the presence of Eimeria species. Samples of litter faeces from each farm were pooled from 10 different random locations within a single broiler house on each farm. In fact, the species composition of coccidial populations is highly repeatable among different broiler houses on the same farm (Jeffers 1974). The evaluation was performed using a polymerase chain reaction (PCR) developed at the Institute for Animal Health (Compton, UK) to specifically detect E. tenella, E. acervulina, E. maxima, E. mitis and E. praecox. Together with this molecular tool for detecting Eimeria species in litter samples, oocyst counts and the evaluation of the percentage of species by using a morphometry test were also performed to further evaluate the samples.
We decided only to look for the five species of Eimeria that usually affect commercial broiler farms -Eimeria tenella, Eimeria acervulina, Eimeria maxima, Eimeria mitis, and Eimeria praecox- due to the fact that E. necatrix has been reported to cause disease in long-lived birds -up to 12 weeks or more- (Williams et al. 1996, Williams 1998) and similarly E. brunetti is often reported to be rare in broilers (Long et al. 1982, Williams et al. 1996, Graat et al. 1998).
Analyzing the 3 species of Eimeria of known and high pathogenic potential (Eimeria tenella, E. acervulina and E. maxima), Eimeria acervulina has been shown to be the most widespread in the four European countries studied, whereas between the two species causing subclinical problems and affecting productivity: E. mitis seems to be quite uncommon, whereas E. praecox was shown to be present in all countries. Combinations of 3 species together were the most common especially: E. tenella, E. acervulina, and E. praecox. E. praecox was found to be highly associated with E. acervulina.

Similar to the study conducted in Europe and using the same techniques of evaluation of the samples, in 2012 HIPRA also performed the first Eimeria spp. prevalence study in South Africa (Pagès et al. 2015)

Analyzing the 3 species of Eimeria of known and highly pathogenic potential (Eimeria tenella E. acervulina and E. maxima) Eimeria acervulina was shown to be the most widespread in South Africa (40.5%), whereas regarding the 2 species that cause subclinical problems and affect flock productivity: E. mitis was less prevalent (7.1%) then E. praecox (9.5%). Combinations of 2 species together were the most common especially: E. acervulina + E. tenella and E. acervulina + E. maxima.
Once again these studies showed the widespread presence of Eimeria praecox and thus of subclinical coccidiosis that “remains one of the most important infections causing decline in production performances” (Haug et al. 2008).
Finally, these results confirmed that the most prevalent species of Eimeria by far is E. acervulina, in contrast with the field perception that most of the time coccidiosis is only caused by E. tenella.