Coccidiosis in Chickens: Symptoms, Evolution & Treatment

By Nick

Coccidiosis is a widespread disease that can quickly wipe out a large part of your flock. It's one of those diseases every chicken owner should be aware of since acting fast is critical in case of an infection.

We'll take you through everything to know about coccidiosis in chickens.

What is Coccidiosis?

Coccidiosis (aka cocci) is a parasitic infection of the stomach and intestines. The parasites on duty are called coccidian protozoa, single-celled organisms that resemble the big brothers of bacteria.

These parasites live in plenty of animals, like dogs and cats, and even humans, but most species have their personalized variety of coccidia. For avian species, they can hop over from geese and ducks to chickens.

Eimeria, a single-celled organism that is causing coccidiosis in chickens

The parasite is exceptionally persistent and can survive multiple years outside the chicken's body. It thrives in dirt and poo. Chickens usually ingest the parasite via contaminated water or food. Once infected, the disease can spread quickly, and the chicken will have red, bloody diarrhea.

Left untreated, coccidiosis can be fatal for your chicken. Luckily you can quickly treat it with antibiotics.

What are the symptoms of coccidiosis in chickens?

The incubation period is 5 to 6 days. Chickens usually go asymptomatic for a couple of days and suddenly become restless and ill on the fourth day after infection. The greatest numbers of deaths occur already on the 5th day.

The most recognizable and well-known symptom is blood in the chicken's droppings. The problem is that chickens regularly have blood in their droppings, which is perfectly normal. They frequently shed their intestinal lining in cecal droppings. You don't immediately have to panic if you see some blood in their poo. However, be careful if their poo is very liquid and bright.

Example of blood in droppings of a chicken to be diagnosed for coccidiosis

And be especially careful if you notice any of the following symptoms:

  • Ruffling of the feathers
  • Weak, restless, lethargic, and falling over all the time
  • Diarrhea and dehydration
  • Pale skin, comb, and wattles compared to other flock members
  • Weight loss and refusing to eat (or growth stop)
  • Laying no (or less) eggs
  • Droopy, dull, or glazed eyes

Chickens fighting a cocci infection are susceptible to other diseases and may show several additional symptoms. Unfortunately, some chickens die from internal damage before showing any signs of illness.

Diagnosis of Coccidiosis

The only way to know if you are dealing with coccidiosis is to get the chicken's droppings checked by a vet. They can quickly diagnose coccidiosis microscopically with a fecal flotation test.

The vet mixes the chicken's stool with a special liquid that makes the parasites float on top. Through the microscope, you can easily recognize the coccidia swimming around. It's the same routine test they use to detect worms and other parasites, so it can be done by any vet, even if they don't treat chickens.

Coccidiosis under the microscope can be easily detected using a float test

Treatment is very effective, especially if it starts soon. Inspection of the droppings can be challenging if the bedding absorbs them. When you suspect something is wrong, use a clean dropping board to capture the poo.

The vet can also make a diagnosis post mortem, which is essential to protect the rest of the flock.

Treatment of Coccidiosis

The most common treatment for coccidiosis is Amprolium. It's a chemical compound that mimics vitamin B1 (thiamin) and prevents the parasite from synthesizing carbohydrates, so it can't replicate and dies. Amprolium is the active ingredient. You can get the drugs over the counter in most countries, albeit under different brand names.

Isolate any infected hens from the rest to prevent further spreading. However, always treat the complete flock, as infected chickens can be asymptomatic. Clean out the chicken coop thoroughly and eliminate all droppings as much as possible. Give some extra attention to the hygiene in their feeding areas and make sure food and water are off the ground.

The blood in the droppings should disappear within 24 hours. The treatment goes in iterations. First, you treat the chickens with medication for a couple of days to kill the living parasites. Then after a couple of days, you repeat the process to kill the parasites that were still in incubation (which is called the prepatent period for parasites).

Vitamin B1

When treating with Amprolium, don't give your chickens extra vitamin B1. It will interfere with the Amprolium that tries to deprive the parasite of its energy sources.

Amprolium, a medicin against coccidiosis, resembles vitamin B1 and mimics it's behavior to prevent coccidiosis to spread

After treatment, you can give some extra vitamin B during recovery, as vitamin B1 is an essential micronutrient that the chicken's body can not make.

Alternatives to Amprolium

Amprolium is not the only possible treatment. Multiple antiprotozoal agents can kill coccidia parasites like Toltrazuril and Sulfonamides. Always follow the recommendations of the vet for the proper medication.

There are no alternatives to proper medicines to treat coccidiosis. However, proper food and supplements can help to boost the chicken's immune system. Some herbs as well as garlic and onion extracts are known to boost the chicken's immune system and improve the microbiome of the intestines. However, they are by no means a replacement for proper medication.

Let's discuss some alternative treatments you might have heard of.

Milk Flush

You might have heard of giving your birds a milk flush to treat coccidiosis. Some people give raw milk to their chickens to provoke diarrhea and clean the intestines. They feed their chickens with yogurt, vinegar, and other probiotics with the idea that the microbes will fight the coccidia in the intestines.

Unfortunately, although they look like giant bacteria cells, these coccidian protozoa are not exactly bacteria. The parasite will not be influenced by other beneficial bacteria or microbes, let alone be eliminated by competitive exclusion.

However, a healthy microbiome is beneficial since the coccidia can wreak havoc on the gut wall. So although probiotics and dairy products will never stop the disease, they can create a healthy environment for fighting coccidiosis and recovery. Scientific research seems to support that assumption. A milk flush to induce diarrhea, on the other hand, will destroy the healthy microbiome.

Diatomaceous Earth (DE)

Some people believe that giving DE to the birds will help against coccidiosis. The underlying idea is that the sharp edges of the fossilized diatoms damage the parasites. Official ATTRA documentation and Indian researchers state that there is no scientific evidence to support this.

That statement largely stands up till now, although some research has found some evidence regarding the use of DE. In 2015, researchers in Poland saw a reduction in Eimeria coccidia after feeding a group of 150 pigeons with grain mixed with diatomite.

Diatomaceous earth for chickens, used in the fight against coccidiosis

The journal of animal science published the results of research performed on lambs, where they observed lower parasite egg counts (175eggs/g vs. 753eggs/g), and they concluded that there may have been a small effect of DE.

Researchers from California and Vancouver found that adding 2% of DE to the diet of egg layers did significantly impact parasite load in the intestines. However, their results varied largely by the breeds. Lowmann Brown egg layers, which are parasite resistant by nature, did not benefit from any DE addition to their feed. But for Bovan Brown hens, adding DE to their diet reduced the amount of Eimeria in the intestines of the chickens. Eimeria is the genus of single-celled bacteria-like parasites that cause coccidiosis in poultry.

Prevention of Coccidiosis

Prevention starts with the vaccination of day-old chicks. If the chicks are not vaccinated, you can opt for medicated starter feed if that's still available in your region. Just don't combine the two. Vaccinated chicks don't need medicated starter feed.

The rest of the preventive measures focus on providing a hygienic, dry and healthy environment for your chickens:

Chicken Owner preparing a hygienic dust bath

Adding probiotics to the food won't help prevent coccidiosis by competitive exclusion directly. The coccidian protozoa are not bacteria. The bacteria or microbes do not influence the parasite and will not take over its place. However, probiotics can boost the microbiome of weak chickens, so they are better prepared to fight off a cocci infection.

Be especially careful with younger chickens. The greatest chance of infection is in birds from four to eight weeks old. They didn't have time to build up any natural immunity yet.

Evolution of Coccidiosis

The lifecycle of coccidiosis is exceptionally complex, and researchers are still uncovering the secrets of this extraordinary part of the animal kingdom. Many details of the core mechanisms were only discovered and described in the last 20 years.

Representation of eimeria protozoa parasite cells with their unique organisms, which are the underlying cause of coccidiosis in chickens

Coccidiosis is not caused by a virus, like fowlpox or Marek's disease.

The parasites responsible for coccidiosis are protozoa, single-celled organisms. These protozoa look a bit like big bacteria, but they come with their own set of exotic cell structures. They are composed of unique organelles like rhoptries and micronemes that seem to be stolen from science fiction literature. Scientists started to realize these protozoa were neither animals nor plants in the eighties. These bastards got their own classification, with the latest taxonomy published as recently as 2000.


There are 50.000 different types of single-cell species in the protozoa kingdom. It's the Coccidia type that is causing the dreaded coccidiosis in animals. And for chickens specific, it's strains of the genus Eimeria. They are part of a group of parasites with the same characteristics, called the Apicomplexa.

Their name is no coincidence, they are called complex, and they certainly live up to their name!

Life Cycle

To understand how coccidiosis develops in your flock of chickens and how to control it eventually, we'll take a deeper dive into the life cycle of these little creatures.

Lifecycle of coccidiosis in chickens, from the oocyst that is ingested, through sporozoites and merozoites and the fertilization phase where gametes form a zygote that is shed out as an oocyst again


It all starts outside the chicken's body, in the dirt, with what's called an oocyst. An oocyst is a parasitic egg that is so exotic and strong that it seems like it's coming from another planet. The shell is even resistant to disinfectants. The oocyst contains a passive form of coccidiosis, and it can survive outside of the chicken's body for multiple years.

Representation of an oocyst that can survive long outside of the chicken's body

When chickens are pecking and scratching in the litter on the ground, they also pick up the tiny oocysts. When an oocyst enters the chicken's body, it immediately activates the coccidiosis strains inside the shell. The chicken's warm and moist internals enable rapid development.

Within 24 hours, new parasitic cellular organisms grow in the oocyst, called sporozoites. These sporozoites are the enemy soldiers that will attack the chicken's body later on.

Representation of the intestins and the traveling of the oocysts to deliver the sporozoites in the chicken's gut


As part of the digestion, chemicals in the stomach and gut of the chicken break down the hard shell of the oocysts. This releases the army of sporozoites inside the intestines of the chicken. The sporozoites attack and force themselves into the gut cells of the chicken.

sporozoites of coccidiosis attacking the chicken's gut cell

When they are inside, they take over the cell and transform it into a factory to create a new kind of parasitic soldier called merozoite.

They create so many merozoites that the original cell will eventually explode. All this happens about four days after the infection. With so many damaged cells in the chicken's intestines, there is plenty of blood in their poo. At this moment, the chicken starts to become seriously ill.


Thousands of merozoites are released into the chicken's body every time a cell explodes. The merozoites are attacking other cells in the body to take over and create even more merozoites. This process repeats multiple times until millions of parasitic soldiers fight in the chicken's body. At this critical point, several chickens will die from internal damage.


After a certain period, the merozoites suddenly stop attacking the chicken's body. They somehow have an attack plan stored in their DNA and know precisely when to stop attacking the chicken from the inside.

fertilization phase of the merozoites of coccidiosis in chickens

Fascinating enough, they start a completely new process where the soldiers suddenly transform into female and male sex cells, called gametes. The sex cells find each other, and - just like in humans - fertilization occurs, which results in the birth of a new parasitic oocyst. This newborn oocyst piggybacks on the chicken's droppings to the outside world. That happens somewhere around the sixth day after infection.


The one oocyst that we started with has now been replicated into half a million new oocysts, spread over the chicken coop, and run. These oocysts are waiting to be picked up by another one of the chickens in the flock. And that's how the disease spreads and can potentially infect the other birds very rapidly.


Coccidiosis is a severe disease caused by a parasite that is very difficult to control. Prevention and vaccination are vital in avoiding coccidiosis in chickens as much as possible, especially in younger birds. It is, however, impossible to avoid altogether. Therefore, it's essential to understand coccidiosis's symptoms and basic mechanics.

Whenever you see blood in the droppings, and you notice any other symptoms, act immediately and check the droppings with a vet. Waiting too long will increase the risk of losing many chickens in your flock.


Nick is a chicken fan, writer, and an all-time chicken fanboy holding a master in engineering. He has a passion for chemistry and he loves running with his border collie that's protecting his flock.

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