Infectious Necrotic Hepatitis in Pigs

Infectious necrotic hepatitis is a severe bacterial liver disease most often associated with Clostridium novyi type B. You may also hear it called black disease in other species. In pigs, it appears to be uncommon, but when it happens, it can cause very rapid illness and sudden death.

The bacteria are spore-forming anaerobes, which means they can survive in the environment and in the intestinal tract for long periods. Trouble starts when spores reach damaged liver tissue and find the low-oxygen conditions they need to multiply. Once active, the bacteria produce toxins that cause liver necrosis and overwhelming toxemia.

For pet pigs and small herds, this condition is especially frustrating because there may be little time between the first subtle change and a crisis. Some pigs show vague signs like lethargy or reduced appetite, while others are found dead without much warning. That is why any sudden illness, collapse, or unexplained death in a pig deserves prompt veterinary attention.

The main cause is infection with Clostridium novyi type B. This organism is considered soilborne and may also be part of the normal intestinal microbiota. By itself, exposure does not always cause disease. The bigger issue is whether spores gain access to the liver and then find the right conditions to activate.

In many species, infectious necrotic hepatitis is strongly linked to preexisting liver injury, especially damage caused by migrating liver flukes. That damage creates oxygen-poor pockets in the liver where clostridial spores can germinate and release toxins. In pigs, the disease is less well described than in sheep and cattle, but Merck notes that pigs can be affected and that C novyi has also been suspected in sudden deaths where obvious liver lesions were not detected.

Other factors that may increase risk include contaminated environments, concurrent disease, and anything that injures liver tissue. Because the condition is uncommon and often diagnosed after death, your vet may also consider other causes of sudden illness or sudden death, including septicemia, toxic exposures, and other clostridial or infectious diseases.

Diagnosis can be challenging in a live pig because the disease often progresses too quickly. Your vet will start with history, recent deaths, housing and pasture exposure, feed changes, and a physical exam of any affected pigs. If a pig is still alive, bloodwork may help assess liver injury and systemic illness, but it may not give a definitive answer.

In many cases, the most useful diagnostic step is a necropsy performed by your vet or a veterinary diagnostic laboratory. Typical findings can include areas of liver necrosis and evidence of severe toxemia. Histopathology and anaerobic bacteriology may support the diagnosis, although clostridial organisms can be difficult to culture if samples are delayed or handled poorly.

Because sudden death in pigs has a broad differential list, your vet may recommend additional testing to rule out other infectious, toxic, or management-related causes. For herd situations, that may include submission of tissues to a diagnostic lab, review of parasite control, and evaluation of environmental risk factors. Prompt sample collection matters, so if a pig dies unexpectedly, call your vet before moving or disposing of the body whenever possible.

Prevention focuses on reducing the conditions that let Clostridium novyi spores activate in the liver. Work with your vet on a herd-health plan that includes sanitation, manure management, feed quality review, and prompt attention to any disease that could damage the liver. If your pigs have pasture access, local parasite risks matter too.

In species where this disease is best studied, liver fluke damage is a major trigger. That means parasite control and environmental management are important parts of prevention when flukes are a concern in your region. Your vet can help decide whether fecal testing, pasture review, or strategic deworming fits your pigs and your area.

Also take sudden deaths seriously. Quick necropsy and laboratory submission can help identify whether infectious necrotic hepatitis is involved and can guide next steps for the rest of the group. In some production settings, clostridial vaccination programs may be considered as part of broader herd prevention, but vaccine use and protocols should be tailored by your vet to the pigs, local disease patterns, and management goals.