When pigs circle, have difficulty standing, or lie down and paddle their legs, many pig farmers feel unable to identify the cause, let alone know where to start with prevention and treatment. Pig diseases that cause neurological symptoms are numerous, with varied symptoms and complex causes, making diagnosis difficult and leading to confusion and misdiagnosis. This article provides a detailed analysis of 9 diseases that can cause neurological symptoms in pigs. Only by understanding the characteristics of each disease and analyzing them comprehensively can a diagnosis be made.
Japanese encephalitis
This disease occurs only during the mosquito season from 7-9 months. Affected pigs develop an elevated body temperature; some have mild paralysis of the hind legs, an unsteady gait, toss their heads, and rush about erratically. Pregnant sows may abort, deliver stillborn piglets, or give birth to mummified fetuses. Boars develop enlarged testicles. The aborted fetuses have cerebral edema, congestion of the meninges and spinal cord, and underdevelopment of the cerebrum and cerebellum; they test positive in the fluorescent antibody test. This is a disease shared by multiple animal species, and its causative agent is Japanese encephalitis virus.
Pseudorabies in pigs
This disease is also shared by multiple animal species, and suckling and weaned piglets are susceptible to infection. When suckling piglets develop the disease, symptoms are most severe. The most typical symptom is the piglet lying on its side, with its legs making paddling movements and a small amount of yellowish-white foam at the corners of its mouth. Affected pigs may have muscle tremors, an unsteady gait, ataxia, and nystagmus. Some pigs develop paralysis of the hind legs and exhibit circling or forward and backward movements. Seizure-like episodes and coma are often also observed. The mortality rate among suckling piglets that develop the disease is high and can reach 100%. Pregnant sows may abort or give birth to stillborn piglets, while fattening pigs commonly show respiratory symptoms. Necropsy may reveal meningeal congestion and increased cerebrospinal fluid, necrotic lesions in the pharyngeal lymph nodes, and grayish-white necrotic spots in the liver and spleen. The disease can occur at any time of year. Administering a gene-deleted pseudorabies vaccine to piglets by intranasal drops at birth, followed by a second immunization with an inactivated vaccine at 45 days of age, can effectively prevent pseudorabies.
Rabies in pigs
This disease is shared by multiple animal species and is usually caused by bites from rabid dogs. Rabies in pigs and pseudorabies are two completely different diseases, although their outward symptoms are similar. Affected pigs may be restless and aggressive, with ataxia, salivation, generalized muscle spasms, aimless running, and itching at the bite site. Eventually, affected pigs become completely paralyzed and weak, and prefer to lie in dark places; some exhibit pica. Necropsy may reveal meningeal congestion and hemorrhage, mild cerebral edema, and intracerebral hemorrhage. Brain tissue is prepared as a touch smear and stained with fluorescent antibodies. Under a fluorescence microscope, the presence of yellow-green fluorescent granules in the cytoplasm indicates a positive result. The pathogen is pseudorabies virus.
Streptococcus suis
Streptococcus has multiple serotypes. Common symptoms fall into three types: encephalitis, arthritis, and septicemia. The encephalitic form of Streptococcus suis occurs mostly in piglets around weaning. The body temperature of affected pigs rises to 40.5-42.5°C. They stop eating and become constipated, and have serous, mucoid nasal discharge. Neurological signs include ataxia, aimless wandering, circling, chewing motions, teeth grinding, and lying on their backs. When the hind legs are paralyzed, they lie on their sides. Acute cases often die about 30 hours after onset. Pigs with the arthritic form may also be present in the herd.
Listeriosis in pigs
This disease is caused by infection with Listeria and is also a contagious disease shared by multiple animal species. Pigs of all types are susceptible, and it occurs most often in growing pigs. Affected pigs have abnormal movement, wandering aimlessly or moving in circles, moving backward, or remaining still with their heads pressed against the ground. They may show opisthotonos or a typical star-gazing posture, muscle spasms or convulsions, lie on their sides with their legs making swimming motions, or have paralysis of some limbs. Necropsy reveals congestion and edema of the brain and meninges, as well as signs of septicemia. Body temperature rises to 42°C. The morbidity rate is low, but the mortality rate is high.
Porcine infectious encephalomyelitis
This disease occurs only in pigs; suckling piglets and nursery piglets are most susceptible. Affected pigs develop an elevated body temperature, become restless and excited, rush forward, circle, and have stiff limbs. They fall repeatedly, experience whole-body spasms and opisthotonos, and adopt a dog-sitting or lateral recumbent posture, eventually becoming paralyzed. On dissection, necrosis and degeneration of some nerve cells in the spinal cord gray matter can be seen.
Porcine edema disease
This is an infectious disease that commonly affects piglets after weaning and is caused by Escherichia coli endotoxin. It is triggered by sudden changes in feed or climate, or by stress. Affected pigs develop edema of the head, neck, and eyelids, sometimes extending to the whole body, and show excitement, circling, spasms, convulsions, and incoordination. Their body temperature is not elevated, and they develop paralysis of the hindquarters. Severe edema is present in the greater curvature of the stomach, the large intestine, and the mesentery.
Tetanus in pigs
This disease is caused by wound infection with Clostridium tetani. It occurs sporadically and generally does not cause widespread outbreaks. Affected pigs show muscle stiffness, visible third eyelids, and tense chewing muscles. In severe cases, the jaws are clenched, the ears stand erect, the head and neck are extended, and the legs are spread apart. They are sensitive to stimuli such as light, sounds, and touch, which worsen the muscle rigidity; they may even be unable to stand. Most cases in piglets are caused by inadequate disinfection during castration.
Congenital tremors in piglets
This disease is commonly known as “piglet shakers.” It is seen only in newborn piglets; sows show no symptoms, and it is not transmitted between piglets. Within the same herd, piglets born early in the farrowing season have more severe symptoms, while those born later have milder symptoms. It commonly affects an entire litter, with more severe symptoms; if only a few piglets in a litter are affected, the symptoms are generally milder. In severe cases, the whole body’s muscles tremble and go into spasms. When the piglets have difficulty moving and cannot suckle, they may starve to death. In mild cases, spasms are limited to the muscles of the ears, tail, or head. Tremors lessen or disappear while affected pigs are asleep, and worsen in response to sounds or touch. Pigs that recover naturally return to normal, but grow more slowly. The cause has not yet been clearly established; it may be due to circovirus and mycotoxins.
Summary: There are many causes of “neurological signs” in pigs. In addition to the diseases mentioned above, they may also be caused by parasites (such as Toxoplasma or cysticercosis) or salt poisoning. The most common causes at present are pseudorabies and the encephalitic form of streptococcal infection. In clinical practice, careful observation and differential diagnosis are essential; identifying the cause allows for the fastest prevention and treatment. In addition to viral diseases, sulfonamides may be somewhat effective against encephalitic “neurological signs.” It is recommended that the initial dose be doubled during treatment.