Coccidiosis remains one of the most economically significant diseases in poultry production, estimated to cost the UK industry in excess of £99 million per year.
Katie Pitman, veterinary technical manager at MSD Animal Health UK, says: "Coccidiosis is a disease of the intestine caused by a single cell gut parasite called Eimeria.
"There are seven species of Eimeria that affect chickens and the severity of symptoms is dependent upon which species is causing the infection. Eimeria maxima and Eimeria tenella are the most common species, with both having a high rate of pathogenicity."
Ms Pitman explains that having an understanding of the life cycle of Eimeria in chickens can really help to comprehend how the parasite causes disease and how it can be controlled.
She says: "The life cycle starts with the excretion of oocysts in the litter from a previously infected bird. At this stage, Eimeria oocysts are unsporulated and therefore not infective.
However, high humidity and warmth in the litter and the circulating air within poultry houses mean that oocysts will sporulate and become infective. Birds are then likely to ingest the infected oocysts and become a new host for the parasite."
The sporulated oocysts replicate several times in the epithelial cells (surface tissue cells) of the gut, it is at this stage that the damage is caused. After several replications, unsporulated oocysts are produced and excreted back into the litter, starting the cycle once again.
Ms Pitman says: "If left untreated, Eimeria species will continue to damage the cells of the intestinal tract, reducing the available surface area for the absorption of food, resulting in poor feed utilisation. This ultimately leads to impaired growth, poor flock uniformity and in severe cases mortality which are all costly to poultry producers."
Controlling coccidiosis in poultry flocks
Ms Pitman explains that there are multiple ways in which coccidiosis can be controlled. She says: "In the broiler industry, chemical treatments and ionophores are generally the dominant method of control either used in combination or alone. Whereas in breeder and layer flocks, vaccines are more commonly used.
"Vaccines are designed to induce immunity safely and as quickly as possible when administered properly.
"The way that the vaccine works is that live sporulated oocysts must be ingested to establish low levels of infection and induce immunity. But, because the strains used in the vaccine have shortened life cycles compared to field strains, fewer reproductive cycles occur before the oocysts are excreted by the bird, hence little damage is caused to the intestinal tissue.
"As the birds become immune, the level of oocyst shedding is reduced and the site is seeded with these attenuated vaccinal strains which do not cause harm to the birds."
Using coccidiosis vaccines on-farm
With some producers using coccidiosis vaccines when chicks arrive on-farm, Andy Payne, key account manager for poultry at MSD Animal Health UK, highlights key point for effective application and uptake of vaccines to develop early immunity.
- Storage - Make sure your choice of vaccine is ordered in plenty of time before the chicks arrive and ensure it is stored correctly i.e., at the right temperature
- Shake well before use - If using a live vaccine, you will need to ensure that it is shaken before use, so oocysts remain within the suspension
- Sprayer calibration - Some vaccines can be applied to chicks via a spraying device. This is usually done while the chicks are still in baskets as they arrive. Ensuring the sprayer is calibrated, and you have calculated how many seconds you need to spray each basket for, will ensure even coverage
- Using a dye - Some vaccines will already include a dye, but this can also be added to the solution. The addition of the colour means you can see where you have been and helps ensure even coverage
- Lighting - With spray-on vaccines, you are reliant on the chicks preening one another to ingest the vaccine. Therefore, keeping lighting bright up to 15 minutes after the vaccine has been applied will mean they are more active and more likely to ingest the vaccine in this time
- Oocyst per gram (OPG) counts - These are a good tool to monitor how well the vaccine is cycling within a flock. Your vet will be able to take the required faecal samples and interpret the results.
