Pericarditis in Chickens: Causes of Heart Sac Inflammation and Flock Losses

Pericarditis is inflammation of the pericardium, the thin sac that surrounds the heart. In chickens, this problem usually does not happen by itself. More often, it appears as part of a broader infection affecting the air sacs, liver lining, or bloodstream. On necropsy, your vet may see fibrin, pus, or excess fluid around the heart.

In backyard and production flocks, pericarditis is often linked to colibacillosis, a disease caused by pathogenic E. coli. Merck notes that poultry colibacillosis can cause septicemia, airsacculitis, pericarditis, and perihepatitis. Respiratory disease can set the stage for this by damaging the airways and allowing secondary bacteria to spread deeper into the body.

For pet parents, the hardest part is that affected chickens may look only mildly ill at first. Some birds become quiet, puffed up, or short of breath. Others are found dead with little warning. Because the visible signs are so nonspecific, pericarditis is usually confirmed after death through necropsy and laboratory testing rather than by symptoms alone.

The most common cause is bacterial infection, especially avian pathogenic E. coli associated with colibacillosis. Merck describes pericarditis as one of the classic syndromes seen with poultry colibacillosis. In many flocks, E. coli acts as a secondary invader after stress, poor air quality, overcrowding, or another respiratory disease weakens the bird's defenses.

Respiratory infections are important triggers. Mycoplasma gallisepticum can damage the respiratory tract, and complicated cases often develop secondary E. coli infection with airsacculitis, pericarditis, and perihepatitis. Infectious bronchitis and other respiratory diseases can also increase the risk of deeper bacterial spread, especially when ventilation, dust control, or litter conditions are poor.

Some viral diseases can cause fluid around the heart rather than classic fibrinous bacterial pericarditis. Merck notes that hepatitis hydropericardium syndrome caused by fowl adenoviruses can produce sudden mortality and straw-colored fluid in the pericardial sac, especially in young broiler chickens. Toxins and metabolic problems can also create look-alike lesions, so your vet may need lab testing to sort out the true cause.

At the flock level, risk factors often include poor biosecurity, mixing new birds without quarantine, contact with wild birds, dirty water systems, high ammonia, damp litter, and delayed removal of carcasses. These factors do not guarantee pericarditis, but they make serious infectious disease more likely.

Diagnosis usually starts with the flock story: how many birds are affected, how quickly deaths are happening, whether there are respiratory signs, and the age of the birds. Your vet will also ask about new bird introductions, ventilation, litter moisture, egg production changes, and any recent stressors. In a live bird, the exam may show weakness, respiratory effort, dehydration, or poor body condition, but these findings are not specific for pericarditis.

A necropsy is often the most useful next step. Merck notes that colibacillosis is diagnosed by isolating a pure culture of E. coli from typical lesions or tissues such as heart blood, liver, or bone marrow from a fresh carcass. Your vet or diagnostic lab may also request bacterial culture, PCR, histopathology, or testing for underlying respiratory pathogens like Mycoplasma gallisepticum or fowl adenovirus.

For backyard flocks, submitting a recently deceased bird can be both practical and cost-conscious. As of May 2025, the California Animal Health & Food Safety Laboratory System lists a backyard flock necropsy fee of $35 for up to 2 birds, while broader poultry/game bird necropsy is listed at $150 per group up to 8 birds. Your local lab's fees may differ, but these numbers give a realistic US reference point.

If deaths are sudden and widespread, your vet may also consider reportable diseases such as highly pathogenic avian influenza. In that situation, do not move birds off the property until you have guidance. Exact testing depends on your flock history, region, and what lesions are found.

Prevention focuses on reducing the infections and stressors that let heart-sac inflammation develop in the first place. Good flock management matters. Merck recommends sanitation of water systems and adequate ventilation to reduce ammonia and dust buildup as part of colibacillosis control. Those basics help protect the respiratory tract and lower the chance of secondary bacterial spread.

Strong biosecurity is especially important for backyard flocks. Extension guidance recommends washing hands before and after entering chicken areas, using dedicated footwear or shoe covers, and changing clothes after contact with other poultry or wild birds. Free-ranging birds where wild waterfowl gather can increase infectious disease risk.

Quarantine all new birds before mixing them with your flock, and avoid borrowing equipment without cleaning and disinfection. Remove dead birds promptly, keep litter dry, prevent overcrowding, and clean feeders and drinkers regularly. If your flock has sudden high death rates or many birds become sick at once, contact your vet right away rather than waiting to see if it passes.

Prevention also means buying birds from reputable sources and talking with your vet about flock health planning. In some situations, testing for respiratory pathogens or reviewing vaccination strategy may make sense. The best plan depends on whether your birds are pets, layers, breeders, or part of a mixed-species setup.