Coccidiosis in Piglets: Symptoms, Diagnosis, Prevention and Treatment

Coccidia are single cell protozoan parasites of the families Cystoisospora (Isospora), Cryptosporidium and Eimeria.

Cystoisospora suis (Isospora) is the main pathogen of piglets and is responsible for the most coccidial diarrhoea.

Understanding the life cycle of coccidia is crucial to implement the right preventive and control measures.

Diagram of the coccidia life cycle in a piglet showing oocyst ingestion, intestinal multiplication, and faecal shedding

• Piglets get infected with coccidia when they ingest sporulated oocysts.
• Coccidia multiply rapidly in the gut lining, damaging a pig's ability to absorb nutrients.
• Oocysts can remain in the environment for a long time and are hard to get rid of.

Piglets are infected during the first week of life following ingestion of oocysts that have sporulated in the environment, especially in high temperatures (32–35 °C) and humidity conditions.

Why contaminated farrowing pens are the main source

There is some debate as to whether the sows contribute significantly to the infection; but the main source of coccidia are the oocysts that are left behind by previous litters. Infected pigs can shed thousands of oocysts in their faeces over the course of the disease. Approximately 50% of piglets excrete oocysts by the end of the first week, and oocysts are seen in the faeces of piglets 5 days post infection.

Illustration of a sow with suckling piglets in a farrowing pen, representing the main environment for coccidiosis transmission

The ease of infection and extent of contamination explains why coccidiosis is present in so many farms. Each oocyst has the potential to destroy thousands or even millions of intestinal epithelial cells. The impact is increased by other infections, such as Clostridium spp.

The main symptom of C. suis infection is scour in piglets (diarrhoea).

It is important to differentiate coccidiosis from other enteric pathologies that show yellowish diarrhoea and appear in the first weeks of life. To differentiate them, consider the following:

• Faeces consistency and blood presence
• The age at which the diarrhoea outbreak takes place
• Response to treatment with different antimicrobials

Table 1: Comparison of diarrhoea aspects according to the enteric pathology (adapted from Swine enteric colibacillosis: diagnosis, therapy and antimicrobial resistance / Andrea Luppi)

Main clinical symtoms

Scour in piglets: Watery or creamy diarrhoea, white to yellow, foul odour. If the diarrhoea is severe, piglets become dehydrated, weak, and can die. Nevertheless, mortality is low.

Yellow diarrhoea from piglets with coccidiosis on the slatted floor of a farrowing pen

Most pigs recover from coccidiosis, but by this point the damage has been done. Stunted growth, contamination of the pens with oocysts and subclinical infections are likely to cause significant losses to the farmer.

Close-up samples of piglet faeces showing different consistencies and colours typical of coccidiosis scour

Faeces pictures University of Veterinary Medicine, Vienna

• Stunted growth: undersized piglets, most evident at weaning
• Dehydration: weakened piglets, sunken eyes

Signs across the litter

• High morbidity: most, if not all piglets get sick.
• Onset of the disease is characteristic and an important clue for farmers and veterinarians. Scouring usually starts at days 7 to 10 of age, rarely 5.
• Low mortality: few piglets die, some recover in just a few days.

Coinfections and their consequences

C. suis also makes piglets more susceptible to other pathogens, namely Clostridium perfringens type A, rotavirus and E. coli. Coinfections increase the mortality rate.

There is evidence that coccidia also changes the gut microbiome, making it easier for the dangerous, toxin-producing bacterium Clostridium perfringens and other pathogenic bacteria to thrive.

What about subclinical infections?

One of the greatest concerns for pig farmers is the presence of subclinical infections. These do not have any clinical manifestations, other than poor performance (pigs continue to waste or underperform after weaning).

Weak piglet lying on the pen floor, illustrating poor performance caused by subclinical coccidiosis infection

Clinical history and symptoms identification can help you to suspect a coccidiosis infection at the beginning.

Pay attention to diarrhoea on the second and third week of age that does not respond to antibiotic treatment.

To get a definitive diagnosis, serial sampling is almost always necessary. You may call your vet to perform laboratory examination.

There are several techniques to see and count the number of oocysts in the faeces, in order to confirm parasites and assess the severity of an outbreak:

• Flotation methods
• Autofluorescence method: oocysts show blue autofluorescence under UV light

Faecal examinations (individual piglets/litter) are required during the second week of age and one week later.

Veterinary faecal sampling of a piglet for laboratory diagnosis of coccidiosis using flotation or autofluorescence methods

At weaning, pigs with coccidiosis will weigh 0.3 to 1 kg less than healthy peers. Additional losses accrue from mortality, cost of treatment, and the impact that oocyst shedding will have in future litters.

Coccidiosis is a costly disease for the pig industry.

Icons illustrating the three main consequences of coccidiosis in piglets: diarrhoea, mortality, and stunted growth leading to loss of profitability

The damage that coccidia do to the gut lining renders it unable to absorb nutrients, which results in worse feed conversion rates (FCR), which in turn results in a much lower average daily gain (ADG). Days to slaughter increase, not only due to the lesser weight at weaning, but also because performance is impacted well into the growing-finishing stage.

Subclinical infections are of great concern because, due to lack of diagnosis, we do not really know what we are facing. There is growing evidence that C. suis might cause some pigs to fade post weaning. Some estimate the impact of subclinical infections to be about half that of clinical coccidiosis.

There is no vaccine for coccidiosis in pigs on the market.

To control this disease, there are three methods at our disposal: hygiene, disinfection, and coccidiostats.

Hygiene

Hygiene is paramount. The main source of infection are contaminated environments.

• Daily removal of faeces is crucial, especially in hot and humid conditions that favour sporulation.
• Control pests which can spread oocysts, such as rodents and insects.
• Thoroughly clean pens between farrowings, especially slurry canals.
• Remove bedding frequently.

Disinfection

Oocysts are resistant to most disinfectants, which poses a new challenge for the pig farmer. Only cresol-based products are effective against coccidia.

• Use disinfectants with proven effectiveness against oocysts (ask your vet).
• Steam-cleaning is effective. Flame guns have also been used; be mindful of your local regulations and think safety first.

Coccidiostats

Coccidiostats are drugs that impede the development and shedding of coccidia. They are effective for the control of infection.

Metaphylactic administration of toltrazuril has also been shown to improve performance, due to its positive effect on subclinical infections. Timing of the treatment intervention is important in order to disrupt the development cycle of parasites — early intervention is more effective.

A single dose of toltrazuril can help prevent clinical coccidiosis. Some products contain toltrazuril and iron, to treat and prevent piglet iron deficiency anaemia while, at the same time, taking care of coccidia.

Once coccidia have colonised the gut lining, treatment is of little value.

Sulphonamides have been used to treat coccidiosis, with poor results. From the perspective of rational use of antibiotics on farm, control of coccidiosis should not be based on use of antibiotics.

A common control practice was to add amprolium, monensin or oral sulfa to sow feed. This protocol is of doubtful value, and it is no longer permitted in all countries. Ask your vet for applicable regulations in your country.

Farm worker holding a piglet during routine health management in the farrowing unit

Many veterinarians choose to treat coccidiosis with injected sulphonamides and provide supportive treatment for dehydration as needed. Scour caused by coccidia is not responsive to antibiotics, a sign that could aid in diagnosis by elimination.

Even if there is not much we can do for an individual pig once scouring is present, we should provide metaphylactic treatment — giving medicine to all animals in a litter, even if they show no clinical signs.

Toltrazuril is the most effective coccidiostat at our disposal. It can be given orally or injected.

A strategy that has proven to be of preventive value is to treat suckling piglets with toltrazuril within the first week of life, with clear benefit of early administration during the first days after farrowing. Once the parasite colonises the gut, there is not much we can do. This prophylactic measure reduces scour, oocyst shedding and improves pig performance.

Injectable toltrazuril products can be effective in preventing coccidiosis with a single fixed dose, which minimises handling and saves labour.

• Early infection through contaminated farrowing pens: Piglets ingest sporulated oocysts of Cystoisospora suis during the first week of life, with contaminated farrowing pens — not sows — being the main source of infection.
• Characteristic diarrhoea onset at 7–10 days of age: Coccidiosis in piglets causes a yellow-to-white, foul-smelling scour that typically appears between days 7 and 10, helping to differentiate it from other neonatal enteric diseases.
• Clinical and subclinical coccidiosis cause significant production losses: Even when mortality is low or visible symptoms are absent, coccidiosis can reduce growth rates, impair feed conversion and contribute to poor performance after weaning. Subclinical infections are particularly important because their impact can easily go unnoticed.
• Hygiene and cresol-based disinfection are essential: Because oocysts resist most disinfectants and persist in the environment, daily faeces removal, thorough pen cleaning, and cresol-based products are critical control measures.
• Prophylactic toltrazuril within the first days of life is the most effective intervention: A single dose of toltrazuril administered early disrupts the parasite's development cycle, reduces oocyst shedding, and improves piglet performance through to the growing-finishing stage.
• Diagnosis requires a farm-level approach: Coccidiosis can be difficult to diagnose, particularly when infections are subclinical. Clinical history, age of onset and response to antibiotics can raise suspicion, but serial faecal sampling and laboratory examination are often needed to confirm infection and assess its extent.

References

1. Shrestha, A., Abd-Elfattah, A., Freudenschuss, B., Hinney, B., Palmieri, N., Ruttkowski, B. and Joachim, A. (2015). Cystoisospora suis — A Model of Mammalian Cystoisosporosis. Frontiers in Veterinary Science, 2(68). doi: 10.3389/fvets.2015.00068