23 The Business of Canadian Hog Farming Better Pork | April 2024 HERD HEALTH CONGENITAL TREMOR Ever wondered why some piglets seem to dance like no one’s watching? By Dr. Hayley Bowling First described in 1922 as “dancing pig disease,” congenital tremor continues to affect farms worldwide. As we learn more about the possible causes of this syndrome, information on strategies for prevention are beginning to emerge. Symptoms Congenital tremor is a neurological condition that affects newborn piglets. Affected piglets present with involuntary shaking of their heads and/or bodies. Typically, piglets with congenital tremor do not shake while they are asleep, but it is constant while they are awake. The tremors may be worsened by stimuli such as handling and sudden noises. Piglets are otherwise normal with no fever or other evidence of systemic illness. Usually, multiple pigs in a litter are affected at a time. “Splay legs” affecting the hind end commonly occur in piglets affected by congenital tremor, which further complicates their ability to move around. The severity can vary widely, from a slight tremor to uncontrollable shaking that prevents them from standing and walking normally. Associated mortality therefore can vary widely as well, from no mortality to significant losses. Increased mortality can result from the inability of affected piglets to suckle shortly after birth, causing reduced colostrum consumption and poor transfer of antibodies from the sow to the piglet. This can result in an increased incidence of scours and other diseases as the piglets are lacking passive immunity from their mother. Reduced milk consumption can also cause reduced growth and increased mortality from starvation. Death can also occur from crushing, as affected piglets are less able to move away from their sow as she lies down. In most cases, the severity of the tremor decreases as piglets age and can be very mild by the time piglets are weaned. Sometimes, however, the tremor can continue into the nursery and even the grower phase. Types and potential causes There are six forms of congenital tremor currently described. They are classified based on various causes. Congenital tremor is grouped into Type A and Type B based on the microscopic changes seen in the central nervous system. Type A typically shows microscopic changes in the cells of the brain and spinal cord such as a reduction of myelination (“insulation”) of the nerve cells. Type B shows no cellular abnormalities. Types AI and AII are caused by viruses that infect the gilt or sow and pass to the developing fetuses during development of the central nervous system. Type AI is caused by classical swine fever virus (CSF or hog cholera). CSF has not been found in Canada and is classified as a foreign animal disease. Type AII is thought to be caused by a recently discovered virus called atypical porcine pestivirus (APPV), also called Pestivirus K. It is thought to be the most common cause of congenital tremor in Canada. This virus is often found in tissues of affected pigs including the brain, tonsils, lymph nodes, spleen, blood, and intestines. APPV may persist in infected pigs for many months (if not for life) and can be shed in feces, saliva, nasal secretions, and semen. Older pigs who are infected later in life typically do not show any symptoms. Most farms notice Congenital tremor usually affects multiple piglets in a litter and most often affects gilt litters. Dr. Hayley Bowling photo
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