Porcine encephalomyelitis, also known as swine polio, is a viral disease that primarily affects the central nervous system of pigs. First identified in the Czech Republic, it was initially referred to as "Jieshen disease." The virus responsible belongs to the Enterovirus genus within the Picornaviridae family, with serotype 1 being the most virulent and the main cause of outbreaks. Other serotypes (2, 3, and 5) are less pathogenic. The virus exhibits strong environmental resistance but can be effectively neutralized by disinfectants such as sodium hypochlorite, 20% bleach, or 70% alcohol.
In terms of epidemiology, pigs are the only natural hosts, with young piglets aged 4 to 5 weeks being most vulnerable. The disease spreads mainly through fecal-oral transmission via contaminated feed or water, though respiratory routes may also play a role. In newly affected areas, the disease can have high incidence and mortality rates, while in endemic regions, it tends to be more sporadic.
Clinically, the incubation period is typically around six days. Early signs include fever (40–41°C), loss of appetite, and lethargy, followed by ataxia, nystagmus, muscle twitching, and head/neck flexion. Severe cases may progress to paralysis, with pigs often lying on their sides or sitting like dogs. Stimuli can trigger abnormal limb movements. Most pigs recover after 3–4 days, but residual paralysis and muscle atrophy may persist. Less virulent strains result in milder symptoms, such as reduced hind leg control, irregular movement, and temporary weakness, which usually resolve within a few days.
Pathologically, lesions are concentrated in the spinal cord’s ventral horn, cerebellar gray matter, and brainstem. Gross changes are minimal, but histopathological examination reveals non-suppurative inflammation, neuronal degeneration, glial cell proliferation, and lymphocytic infiltration. Eosinophilic inclusion bodies are commonly found in neurons, and prolonged infections may lead to muscle atrophy.
Laboratory diagnosis involves isolating the virus from the cerebellum and spinal cord of infected pigs, followed by inoculation into susceptible animals. Serological tests, such as neutralization assays, immunofluorescence, and ELISA, are also used. Neutralizing antibodies can remain detectable for up to 280 days, making them valuable for confirming past infections.
Differential diagnosis includes conditions like porcine hemagglutinating encephalomyelitis, listeriosis, and pseudorabies. Each has distinct clinical features: for example, porcine hemagglutinating encephalomyelitis is more common in very young pigs and causes red blood cell agglutination, while listeriosis presents with septicemia and liver necrosis. Pseudorabies, on the other hand, often leads to reproductive failure in sows and severe neurological symptoms in piglets.
There is currently no specific treatment for porcine encephalomyelitis. Supportive care, including hydration and nursing, can help improve recovery. Some experimental treatments, such as using serum or blood from recovered pigs, have shown limited success. Prevention focuses on strict biosecurity measures, quarantine of new animals, and vaccination. In outbreak situations, inactivated or attenuated vaccines may be used, and sows can be exposed to mild infection before farrowing to build immunity and protect their offspring. Rapid diagnosis and isolation are critical to controlling outbreaks and preventing further spread.
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