Age affected: Newborn, weaners, growers / finishers, gilts, sows, boars (also affects humans, bats, cats, dogs, rats, horses).
Causes: Nipah virus.
Effects: Coughing, fever, respiratory distress, off food, trembling, head pressing, spasms, leg weakness, abortion, stillbirths, death.
Nipah disease is caused by a paramyxovirus called Nipah virus, closely related to the Hendra viruses which have been found in pigs and horses in Australia and which have been associated with fruit bats. The virus has been grown in cell culture, but has been assigned to Hazard Category 4, the highest, because of its effects on man (56 people died of 164 infected in the original outbreak). Infection enters farms in carrier pigs and then spreads by aerosol or contact. The disease affects the lungs but also causes septicaemic signs and can reach the brain to cause central nervous system lesions. Recovered pigs develop antibody.
Mode of transmission
The virus is present in respiratory secretions and spreads from pig to pig via the oronasal route. It originates from fruit bats and is introduced to pigs from their excretions. It can infect a wide range of species including humans. Spread from farm to farm is in carrier pigs, but movement of other infected species may also be involved.
The clinical signs vary with the age group affected. Recently weaned, growing and finishing pigs develop coughing which may be mild, moderate or severe and prolonged almost to the point of retching. Adults are more severely affected, with sows developing moderate dyspnoea (difficulty in breathing) nervous signs, inability to stand, convulsions and die within 6 hours of the onset of convulsions.
Entire litters of sucking piglets may be lost with the sows. They lose condition extremely rapidly prior to death as a result of starvation of the effects of the disease. Boars also develop dyspnoea and convulsions, but have a thick mucopurulent discharge from the nostrils which are covered in flecks of mucous. Affected pigs may develop convulsions prior to death but appear congested (blue) just prior to death which occurs within 6 hours of the onset of the clinical signs. Some animals may become infected and seroconvert without clinical signs being obvious.
Nipah disease occurred in Malaysia and should be suspected in South East Asia where older pigs develop a rapidly fatal respiratory disease in which nervous signs also occur. There may be a history of pig movement from another outbreak or of contact with fruit bats. Clinical signs of headache leading to encephalitis, coma and death may occur in humans in contact with the pigs and similar signs occur in dogs, cats and horses. The past presence of the disease in a herd can be confirmed by a specific IgG capture ELISA using Nipah virus as antigen which can detect specific antibody.
The post-mortem appearance of dead pigs may be suggestive. There is a dependent lobe pneumonia in affected pigs with the intermediate lobe being most severely and consistently affected. The interlobular septae are prominent. The kidneys are enlarged and both the cortex (rim) and medulla (substance) are petechiated (spotted with bleeding points). Haemorrhages have been seen on the brain although not in every case. Similar lesions are present in the other affected species. The virus may be isolated from the affected lung or kidney and demonstrated in the lesions.
Treatment and prevention
There is no treatment. The Malaysian government adopted a slaughter policy and most parts of the world have made the disease notifiable to state veterinarians if suspected. The risk to human health has been of major importance in control. Where the disease is suspected, overalls, mask and goggles should be worn. Affected pigs were slaughtered, the carcasses destroyed and the farms disinfected thoroughly.
Tracing of infected pigs was carried out and all those found slaughtered. Serological testing in the area using the IgG capture ELISA developed in Malaysia resulted in the detection of a few other infected farms where the pigs were then slaughtered. A total of 900,000 pigs were destroyed. At the time of writing the disease has been eradicated, but its ability to move from farm to farm in carrier pigs and the threat it poses to man make it important that it should be identified promptly and eradicated should it ever recur.
Fatal infections can occur in humans. The disease is notifiable and reportable to governments and to OIE.