All Cooped Up: Coccidiosis
All Cooped Up is a new feature, profiling poultry diseases and how to prevent/treat them, written as a collaboration between medical professional Lacey Hughett and University of Pennsylvania poultry specialist Dr. Sherrill Davison.
What is it? A microscopic parasitic infection of the digestive tract.
Causative Agent: Multiple different protozoal species of the genus Eimeria.
Incubation period: Dependent on species, the amount of coccidial oocysts are ingested and the severity of the infection.
Disease duration: Recovery can take two weeks or longer.
Morbidity: Can be very high, depending on the severity of the infection.
Signs: Blood or mucous in the droppings, diarrhea, weakness, listlessness, decreased food and water intake, pale comb and skin, weight loss, death.
Diagnosis: A fecal float test, or by scraping and testing the intestines of a deceased bird.
Treatment: Prevention is the best treatment, otherwise medications such as amprolium.
Coccidiosis in poultry is a common protozoal disease affecting the intestinal tract. It is predominantly characterized by diarrhea and intestinal inflammation. It mainly afflicts chickens and turkeys and is found on a global level. The infective agents are several species of Eimeria and are collectively part of the Coccidia subclass. Coccidia are single-celled, obligate, spore-forming parasites. Coccidia infect a wide variety of animals and are host specific.
There are several Eimeria species and the severity of the disease process depends on which strain is present. Currently, there are nine known species that affect chickens and seven that affect turkeys, all with slightly different presenting factors. Luckily, Eimeria are also species-specific, so varieties of the protozoa that affects chickens cannot pass on to turkeys.
Coccidia spread through the fecal-oral route, so birds become infected by coming into contact with and consuming feed, water, dirt, or bedding that has been compromised with infected feces. The protozoa are referred to as an oocyst, and the infective unit is called a sporulated oocyst. Spores get into a clean flock by traveling there through an infected bird or carrier. Think biosecurity.
Upon ingestion by the host bird the oocyst releases sporozoites. Sporozoites are minute cells that go forth and initiate reproduction of the disease in both sexual and asexual cycles. This leads to the development of thousands of new oocysts in the intestines, where they are shed by the host to sporulate and infect the next bird. A single infective oocyst can create over 100,000 new oocysts within a flock.
Intestines are made up of epithelial cells whose job is to collect the nutrients and water necessary for survival before it passes from the body. It is in these cells where the oocysts grow and reproduce, causing significant trauma. Lesions appear as the oocysts destroy these cells, leading to the primary sign of coccidiosis: Mucous and blood in the stools. If the infection is bad enough the bird will be losing a significant amount of blood, which is the rationale behind the pale comb and skin. The amount and severity of lesions present are directly related to how many sporulated oocysts the bird has ingested.
If exposure to the coccidia is only moderate, the host bird may not show any definite signs or symptoms. This is due to the bird developing short term immunity. Just like vaccines, if a bird is exposed to frequent, small levels of the pathogen they will build up an immunity to that variety. Unfortunately, they will still be susceptible to varieties they haven’t encountered and in addition, it is very possible for a bird to become infected with multiple strains of the pathogen at once.
Since there are many species of coccidia, it can be difficult to determine on symptoms alone which strain is afflicting a flock. Identification of the strain can be done by the microscopic features of the specific cell and the nature of the infection. Different strains affect different areas of the intestinal tract and can create different kinds of lesions. There are also some variations on the sporulation times, and diagnosis is done by a fecal examination or necropsy examination of a deceased bird. Despite the strain, treatment is the same no matter what strain is involved.
The most predominant problem associated with a coccidiosis infection is a compromised immune system, opening the door to secondary infections. Coccidiosis can also lead to necrotic enteritis, which is a secondary intestinal bacterial infection with a high mortality rate.
Prevention is the first step to a healthy flock. Coccidia love humidity and warmth. Warm weather and wet conditions encourage the sporulation of the oocysts and even a seemingly small amount of water can lead to sporulation. Biosecurity is important in preventing a coccidia outbreak. Oocysts can come into contact with a flock by insects, people, equipment, other animals, feed, or bedding.
In addition to excellent biosecurity, vaccines and anticoccidials can be utilized. Chicks can be fed small amounts of the pathogen on gel puck applicators to help develop immunity when they are young, and adult birds can be given anticoccidial compounds directly in their feed. Most importantly, it is crucial to not overcrowd birds and maintain dry and clean bedding. Straw bedding should be avoided because it is difficult to keep dry.
Treatment is straightforward. Medications need to be used, but to ensure the correct drug is provided for the flock, it should be provided by a veterinarian or poultry specialist. Amprolium is used most frequently. Certain antibiotics, like those from the sulfa family, should not be used in layers. Providing additional vitamin K and vitamin A with help with recovery and help reduce the mortality rate.
Coccidiosis can be a costly and devastating disease, but it can be prevented and treated early through good flock management.
All information in this article has been vetted for accuracy by Dr. Sherrill Davison, Poultry Specialist at University of Pennsylvania School of Veterinary Medicine.
Originally published in the December 2019/January 2020 issue of Backyard Poultry and regularly vetted for accuracy.