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Avian Coccidiosis

Coccidiosis is an intestinal tract infection caused by several species of the protozoan parasite Eimeria (sometimes referred to as coccidia). Different species of coccidia target specific organs and areas of the body---such as the intestinal tract, kidneys, liver, and some throughout the body in red blood cells. The severity of the infection (and resulting damage to the chicken's gastrointestinal tract) depends on the number of oocysts ingested and the general health and immunity of the bird.

Although over 1000 species of Eimeria have been identified across numerous animal species, there are nine Eimeria that are of main concern for chickens. The species of Eimeria reported as highly pathogenic are E. acervulina, E. brunetti, E. maxima, E. mitis, E. necatric, E. praecox and E. tenella. Mildly pathogenic species include E. acervulina, E. mitis, and E. mivati, whereas E. praecox and E. hagani are considered to be the least pathogenic.

Chickens become infected by ingesting sporulated oocysts (coccidia "eggs") from the surrounding environment. Chickens who have previously been infected, may develop immunity to the specific species of Eimeria in their environment. However, if their immune system is lowered due to infection with another disease, stress, or exposure to a new species of Eimeria , they may develop coccidiosis. Outbreaks in flocks often occur when birds are stressed, overcrowded, and living in poor sanitary conditions. Even seemingly healthy flocks may be infected with Eimeria, without showing any signs of disease.

When young chickens are exposed to Eimeria early on, as long as there are not excessive levels present in the environment, they will usually develop a natural immunity, without any treatment necessary. Emphasis should be placed on keeping their environment as clean and dry as possible. If excessive levels of Eimeria eggs are present in the environment (such as what would happen when birds are overcrowded), and/or birds become stressed, they will likely require treatment. When adult chickens are introduced into a new environment, without having prior exposure to the particular species of Eimeria while younger, they will not have developed immunity and be very vulnerable to the disease.

The resulting damage caused by Eimeria to the chicken's intestinal lining results in the leakage of proteins, including plasma into the the bowel. This not only interferes with the ability to digest nutrients, but it also greatly increases their risk of developing Necrotic enteritis (NE), allowing Clostridium perfringens to replicate rapidly.

Symptoms of Coccidiosis in Chickens

Signs of coccidiosis in chickens varies depending on the number and species of Eimeria present, site of infection, and the age and overall health status of the bird.
Dysentery is a common sign that occurs when infections are severe---consisting of the appearance of blood and mucus in the feces. Affected birds may also appear fluffed up and depressed (will show decreased activity levels and disinterest in normal chicken activities). They may loose weight or show reduced weight gain if affected during early growth.

How Coccidiosis is Diagnosed in Chickens

Coccidiosis is diagnosed in chickens through a fecal test on the chicken's droppings. Eimeria eggs can be identified when the feces is looked at with a microscope. A Complete Blood Count (CBC) may show decreased red blood cell and total protein level counts in affected birds.

Coccidiosis Treatment for Chickens

Treatment of coccidiosis involves several important components:
  • Anticoccidial agents. It is initially important to control the coccidia with an anticoccidial agent such as amprolium or toltrazuril, in accordance with the manufacturers recommendations.
  • Antibiotics: It is important to control secondary bacterial growth by concurrently administering antimicrobials such as tylosin or amoxicillin. When coccidiosis damages the intestinal wall, it leaves the bird more at risk of developing secondary infections, such as necrotic enteritis.
  • Supportive care: It is very important to keep the bird hydrated and comfortable.
  • Environmental/Management Changes. Slow down oocyst sporulation within the environment where birds live by regularly cleaning the area where chickens live, by removal of the feces and soiled bedding, ensuring it is kept dry (perhaps install better drainage or roof to prevent rain), and/or rotate birds to different areas often. Do not overcrowd birds.
There has been an increased emergence of drug-resistant strains of Eimeria, especially after prolonged uses of the drug. Therefore, it is important to conduct a follow up fecal test following treatment, to evaluate whether the drug was effective against the particular strains of Eimeria present.

Clinical Signs

Hunched up with ruffled feathers
Change in droppings (water, mucous, and blood)
Loss of appetite
Loss of condition
Diarrhea/watery droppings
Stunted growth rate


  • History
  • Clinical signs
  • High fecal oocyst counts (over 50,000 oocysts/gram of feces)


AmproliumMost be given for 5 days straight to be effective.
Toltrazuril6 mg/kg added to drinking water for 2 days. Note - When Toltrazuril is administered, it is important NOT to concurrently give supplements that contain vitamin B, for it will override the effects of the drug.
Sulphonamides2-3 days of daily treatment and repeated in 5 days.
IonophoresWhat is added to 'medicated' chick feed.
VaccinesThere are two types of vaccines that are currently usedlive unattenuated (Coccivac, Advent, Immucox,and Inovocox) and live attenuated (Paracox, HatchPak CocciIII) vaccines.
Supplemental vitaminsMany anticoccidial drugs interfere with the chickens ability to absorb important nutrients; also helps boost their immune system to help them fight off the infection.
AntioxidantsFruits and herbs which contain a good source of antioxidants has been shown to be beneficial---sources such as cranberries, pomegranate, green tea, grape seed extract, rosemary, oregano, curcumin, and many more. Use our herbs and essential oils look up tool.
Essential oilsEssential oils of artemisia, thyme, tea tree, and clove have been shown to be of benefit. Use our herbs and essential oils look up tool.
AntibioticsMay be needed in some cases depending on the severity of the disease.
Supportive care
Environmental modificationsImprove sanitary practices by regularly cleaning the environment where birds are kept, minimizing risk of fecal contamination in feeders and waterers, and expand enclosure or coop area if overcrowding birds.



  • Clean, disinfect, and refill waterers with fresh water daily, to prevent buildup of potentially pathogenic organisms. Position them so as to minimize water spillage onto bedding litter, as moisture promotes the growth of cocci.
  • Do not overcrowd birds.
  • Don't keep birds in the same enclosed area for extended lengths of time, rotate them periodically to another area
  • Keep chickens of different ages separated
  • Practice good sanitation and minimize accumulation of feces by cleaning at least once a week.
  • Design roost areas over screened dropping pits for feces, to minimize contact birds have with feces.
  • Provide apple cider vinegar in the drinking water (1 tablespoon per 5 gallons of water)
  • Purchase resistant poultry breeds, such as the New Hampshire, Rhode Island Red or Leghorns

Scientific References

Good Overviews

Age Range

Coccidiosis occurs most frequently inchickens between 4 to 5 weeks of age.

Risk Factors

  • Overcrowding
  • Mixing chickens of different ages together
  • Unsanitary living conditions (large accumulation of feces)
  • Stress (recent transport, change of ownership or flock mates, sudden temperature change, bullying, stalking predators, improper handling, injury, etc.)
  • Concurrent disease
  • Poor immune status
  • Introduction of a new chicken into the flock
  • Letting chickens recovering from an illness or injury back out into the flock prior to finishing the course of medication