Chickens that are kept on litter floors, are easily susceptible to coccidiosis. The parasite causing this disease, is difficult to conquer. Understanding and recognising the disease however, will help controlling it and allow the birds to keep a healthy gut.
By Hilde Van Meirhaeghe and Maarten De Gussem, poultry veterinarians, Vetworks, Belgium
Coccidiosis is probably economically the most important disease in poultry. “Today it may be difficult to appreciate the devastating effects that these parasites once had on poultry flocks. Indeed, without adequate means of control, both by chemotherapy and vaccination, it is possible that the modern poultry industry could not have developed to its present extent,” says Prof. D. Chapman, known coccidiosis researcher, in his latest review of the disease in Poultry Science.
Major economic impact
In general, gut health is a crucial prerequisite for an economically viable broiler industry. The value of converting feed into meat in poultry production can be roughly calculated: 52 billion birds consuming each 4 kg of feed requires 208 M metric ton of feed produced globally in the professional poultry industry. Estimated is that on average, per 2.5 kg live-weight-bird, about €0.10 of production is lost by suboptimal coccidiosis control and a similar €0.10 is lost by suboptimal bacterial enteritis control, together on average leading to over €10 billion losses in the poultry industry. Very important is the finding that almost 70% of this estimated cost is due to subclinical coccidiosis, by impact on weight gain and feed conversion rate. One of the reasons for these remarkable findings is probably the difficult diagnosis of subclinical coccidiosis. Obviously, as this cost is an average, some companies will have much lower and some much higher costs due to these two most important intestinal disorders.
Lesion scoring system
In order to evaluate the level of control and to interpret the added value of additives, feed strategies and management procedures, scoring broilers at different ages is a common procedure in order to evaluate coccidiosis levels since a widely accepted gross lesion scoring system has been introduced. Recently, a harmonised scoring procedure for bacterial enteritis, of which coccidiosis is the most important primary cause, has been proposed and is gaining popularity in order to have a more complete picture of the gut health status of broiler flocks, in order to more objectively enhance modifications and improve technical thus financial performance of poultry operations.
Coccidiosis is a disease caused by protozoan parasites of the genus Eimeria, developing within the intestine of most domestic and wild animals and birds. In chicken there are seven different species, each species has a predilection for a specific part of the intestine and provoke different types of lesions. The most important species in broilers are E. acervulina, E. praecox, E. maxima, E. mitis and E. tenella. Longer living birds, layers and breeders, can also be infected with E. necatrix and E. brunetti.
Direct life cycle
Eimeria species have a direct life cycle, so there is no intermediate host needed to complete the cycle. The life cycle of Eimeria takes about four to seven days to complete. Infectious, sporulated oocysts are picked up by the bird from the litter. Different asexual stages invade intestinal cells to replicate, inside the cell the parasite divides and invades more cells, in the last sexual stage a male and a female gametocyt unite and form new oocysts that are shed in the faeces.
In order to become infective, the oocysts have to sporulate, this requires specific conditions of moisture, temperature, and oxygen in the environment. The oocyst is very well armed to survive and difficult to destroy with disinfectants, it can survive several years on a farm.
Not all are the same
The seven species of Eimeria infecting chickens are not considered equally important. The pathogenicity depends on the affected region in the intestine, the invasion of the mucosa, deep or superficial, the reproductive capacity and the number of asexual cycles needed to complete the life cycle of the parasite. Depending on the species, magnitude and site of infection, coccidiosis can result in a limited enteritis resulting in fluid loss and malabsorption of nutrients, inflammation and destruction of the intestinal wall resulting in extensive haemorrhage and death.
Generally, it is agreed that of the species recognised in broiler chickens, the most pathogenic are E. acervulina, E. maxima and E. tenella. The latter is, amongst broiler farmers, the best known. It infects the caeca and because of wide-spread damage with distinct gross lesions and loss of blood in the faeces, it is easily recognised also by farmers.
On the other hand, when performing field necropsies on a larger scale, E. tenella appears to be the least prevalent of the three species mentioned. Also, because the damage is limited to the caeca, the effects on growth and feed conversion rate are minimal. Diagnosis of clinical disease caused by E. tenella is quite easy and action (therapy on the short term, change of preventive means on the long term) can be accomplished quickly. These facts make its impact on the productivity of the broiler industry relatively limited compared to the other species, although many broiler farmers associate coccidiosis only with caecal coccidiosis.
E. acervulina and E. maxima, both much more prevalent, are less perceived to be related with clinical coccidiosis in the field. E. acervulina causes white spots or ladder like lesions in duodenum and in heavier infections also in the upper jejunum. E. maxima causes pinpoint haemorrhages and sloughing of epithelia in the midgut resulting in orange mucus in the droppings. To assess the level of damage caused by these two species, lesion scoring can be performed.
E. praecox and E. mitis do not provoke specific lesions and are completely disregarded using the lesion scoring method, even though both species have been shown to be able to cause losses through an increased feed conversion rate and in the latter case even morbidity.
Species causing most spectacular lesions, are erroneously considered to be the most important ones, because losses from coccidiosis are not due to clinical disease but mainly caused by lower performance due to subclinical infections.
Birds with clinical cases of coccidiosis are depressed, standing in a hunched position and the feathers are standing upright. The birds are chilly and stay under the heat source. Droppings are abnormal: watery or bloody and orange coloured slime. One of the first signs of clinical and even subclinical coccidiosis may be paleness. Mortality increases. At necropsy, typical lesions can be found for different species (see photographs).
Clinical coccidiosis is the tip of the iceberg, before there is an outbreak, performance will suffer due to subclinical coccidiosis. In the subclinical form of the disease, the parasites are causing damage to the intestinal cells and the mucosal barrier. Not only is absorption impaired, there is an inflammatory reaction and a shift of the microbial community resulting in bacterial enteritis or dysbacteriosis and contributing to wet litter problems.
Signs during necropsy associated with the conditions described are:
During a visit in a typical affected poultry house, signs frequently encountered include:
During a typical episode of bacterial enteritis the WFR exceeds 2 in normal ambient conditions. In a later phase, water consumption also stalls. Because of wet litter, birds have dirty feathers and feeding and drinking activity is reduced.
Three predisposing factors
Because in affected animals, Clostridium perfringens (Cp) has been isolated in much larger numbers and more proximal in the GIT than in healthy birds, bacterial enteritis (BE) is often associated with necrotic enteritis (NE). Three predisposing factors are associated with BE: feed ingredients known to cause BE, (subclinical) coccidiosis, and management. As bacterial enteritis is today one of the most important problems affecting the performance of the broiler industry, the role of coccidiosis in this multi-factorial condition must be carefully assessed.
What to do
If there is an outbreak of coccidiosis on a farm it is important to consider actions on the short and on the long term. To treat immediately to avoid further losses, but also to adapt the anticoccidial programme for the next flocks. Therapeutic anticoccidials such as toltrazuril, amprolium and sulphonamides can be given in drinking water. Because of the risk of developing resistance, these medicines should be reserved only for therapy and not for prevention.
There are two means of preventing coccidiosis: chemoprophylaxis and vaccination. Chemoprophylaxis using so-called anticoccidial products (ACP) or anticoccidials in the ration is by far the most popular, but reduced sensitivity and resistance are increasingly important as no new anticoccidial compounds are known to be under development. Development of resistance can be avoided by using these ACP in rotation programmes.
Also live attenuated and non-attenuated vaccines are available, but in addition to cost, the fact that live vaccines need host cells to replicate and to instigate an active immunity, cause them to result in subclinical coccidiosis and this is a disadvantage. This is associated with a diminution of performance and, in the absence of growth promoters, even attenuated vaccines are considered by many poultry producers to be associated with a higher incidence of bacterial enteritis. On the other hand, the main advantage of the live vaccines is their ability to alter the level of resistance in a coccidial population by replacing the field population of resistant strains with vaccine strains that are sensitive to ACP. The approach of live vaccination to optimise the efficacy of anticoccidials is very important and in addition to simple resting of anticoccidials is the fastest and most efficient method known to help reduce the portion of resistant parasites in a given coccidial population. Simple resting of (classes of) anticoccidials will also, in most cases, lead to an improved sensitivity status to that (class of) anticoccidial, but it will take a lot more time to achieve a similar improvement.
Cost and efficiency
To control coccidiosis, today it is more and more recognised that a rotation with using both anticoccidials and vaccines provide the best reduction of costs from both coccidiosis and subsequent bacterial enteritis. Cost and efficiency of a programme should be evaluated by considering performance over a number of flocks, not just one cycle. In recent field trials in Benelux, improvement by rotating vaccines with anticoccidials was over 2 grams extra ADG and FCR2000 improvement of more than 8 points!
Climate and housing
Important for the parasite to complete his life cycle are the environmental conditions that, after being shed with the faeces by the bird, allow the oocysts to sporulate. Therefore, climate and housing conditions are key factors in coccidiosis control.
In humid and hot climates the parasite can replicate more efficiently and infection pressure will build up more rapidly. Optimising climate control inside the house will have a beneficial effect to control wet litter and minimise conditions that favour bacterial enteritis.
References are available from the authors: www.vetworks.eu
[Source: World Poultry – Managing Coccidiosis 2014]
Interaction with the intestinal microbial ecosystem: The link with bacterial enteritis(dysbacteriosis)
1. Gut cells damaged by coccidiosis: proteins leak into the gut from the cells.
2. Gut villi fuse together and become shorter: smaller surface available for bacteria to adhere to but also for intake of nutrients, so nutrients will be available to bad bacteria for longer.
3. Mucus lining on gut cells thickens: more difficult for bacteria to adhere to but also inhibits nutrient absorption from the lumen (intestinal cavity). More gut cells suffer serious damage. Conditions more favourable for bad bacteria.
4. Inflammation occurs around damaged gut cells: the gut wall reddens and softens, and gut villi can be destroyed, resulting in little or no further absorption of nutrients. Bad bacteria flourish and cause even more damage to the gut.