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.

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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 administer a live PRRS vaccine to animals already infected to stop the piglet’s infection?

Summary: 

Vaccinating the infected sows with a PRRS live vaccine does not seem to help to reduce the clinical signs. It normally reduces the clinical signs in sows when the vaccination is administered before the infection with the field virus. The non-immunised gilts are animals that can help in the replication of the virus on unstable positive farms, and because of this, the vaccination and adaptation before their introduction on the farm is recommended to reduce the clinical signs in these animals and to lower the circulation of the virus on the farm.


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A PRRS outbreak is causing 40% of stillborn piglets. Is it possible to administer a live vaccine to animals already infected to stop the piglet’s infection? Could a vaccine of this kind reduce the number of dead piglets and stop the transmission to new litters?

In this case, an outbreak of stillborn piglets (around 40%) is described, and it is suspected that the cause is PRRS. When we ask for more information on the case, we are told:

Most of the affected litters belong to first parity sows.

No PCR diagnosis of PRSSV on deadborn piglets has been carried out.

Gilts come from another farm, their health status regarding PRRS is unknown, and they are not vaccinated.

The semen used for AI has an external origin.

Vaccinating a newly infected animal with the PRRS field virus does not have practical advantages for the animal, because the immune system already has a strong antigen to process the answer needed. The difficulty does not lie in the individual animal, but on an animal population, because not all the animals become infected at the same time. The PRRS virus is not very contagious, and because of this, the contamination of all the sows on the farm with the field virus will take a long time if we leave the virus to circulate naturally. In these cases, the clinical symptomatology will go on until the last sow becomes immunocompetent against the virus. This can take several months or even years, when negative subpopulations appear on positive farms.

PRRSV-naive gilts are another source of active virus replication when they enter an unstable farm with an active virus circulation. In this case, a situation like the one described can appear. Nevertheless, to be sure, we must diagnose if the PRRSV is the agent responsible for the mortality of the piglets.

If the PRRSV diagnosis is confirmed in the piglets and the gilts that come from an external source, the next step is to reduce the virus circulation on the farm, mainly in the gilts, that may be where the virus proliferates. In cases like this, we recommend vaccinating all the sows to induce some kind of immunisation against the PRRSV and to reduce the clinical symptoms in the sows NOT infected at the time of vaccination. We are not going to avoid the infection of new litters with the field virus, but we can reduce its negative impact and the clinical signs if there is an immunisation previous to the infection.

There is the risk of not achieving enough immunological protection against the field virus with some vaccines, but as of today there is not a technology that allows us to say, with confidence, which is the most effective vaccine for a certain farm. Even after sequencing the virus and choosing the vaccine with the highest homology degree, nothing guarantees us that it will be the most effective one on the farm.

The strategy that we use in clinical outbreaks like this (with a confirmed PRRS diagnosis) is:

The vaccination of all the sows and boars on the farm with a live vaccine on the same day (we will vaccinate the most immunodepressed sows the following week: on the insemination/mating week and the farrowing week). The goal is to obtain a quick immune response against the PRRSV in all the sows in the group, and we expect a certain degree of cross-protection between the vaccine and the field strains. Revaccinate 4 weeks later with the same protocol. 

The gilts that enter the pregnancy stage must be well immunised and non-viraemic (PCR-negative to PRRS and IgG-positive). The vaccination and adaptation of viraemic animals on the farm and allowing enough time in quarantine until they do not excrete the virus (12 weeks is normally enough) are recommended. This is very important for the future control of PRRS on the farm. 

Buying PRRS-negative semen to inseminate the sows. 

Knowing if the virus is circulating in the nurseries. If there is circulation, implement biosecurity rules to reduce the transmission of the virus to the sow herd. 

After the second vaccination of the sows, evaluate if there are still viraemic piglets at birth. If this improves, we can keep the vaccination and adaptation programme only in the gilts in quarantine. 

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.