Abstract
Congenital tremor type A-II in piglets has been regarded as a transmissible disease since the 1970s, possibly caused by a very recently-described virus: atypical porcine pestivirus (APPV). Here, we describe several strains of APPV in piglets with clinical signs of congenital tremor (10 of 10 farms tested). Piglets on a farm with no history of congenital tremor were PCR-negative for the virus. To demonstrate a causal relationship between APPV and disease, three gilts were inoculated via intramuscular injection at day 32 of pregnancy. In two of the three litters, vertical transmission of the virus occurred. Clinical signs of congenital tremor were observed in APPV-infected newborns, yet also two asymptomatic carriers were among the offspring. Piglets of one litter were PCR-negative for the virus, and these piglets were all without congenital tremors. Long-term follow up of farm piglets born with congenital tremors showed that the initially high viremia in serum declines at five months of age, but shedding of the virus in feces continues, which explains why the virus remains present at affected farms and causes new outbreaks. We conclude that trans-placental transmission of APPV and subsequent infection of the fetuses is a very likely cause of congenital tremor type A-II in piglets.
Highlights
Congenital tremor is a well-known phenomenon in newborn piglets [1], which was first described in 1922, when ‘dancing pigs’ were described by Kinsley [2]
An outbreak of congenital tremor type A-II was diagnosed on a pig farm (Farm 1) located in the Netherlands in early 2012
Piglets born from gilts were primarily affected, and piglets born from higher parity sows occasionally showed clinical signs
Summary
Congenital tremor is a well-known phenomenon in newborn piglets [1], which was first described in 1922, when ‘dancing pigs’ were described by Kinsley [2]. Viruses 2016, 8, 271 articles have been published that describe the same clinical signs under varying names, including shaking pig disease, tremor in pigs, and myoclonia congenita [3,4]. Congenital tremor is characterized by tremors of the head and limbs that vary in severity, but are reducing or even absent during sleep. These tremors can be aggravated by stress, for example excitement and cold. They last for several weeks to months, but most piglets are clinically normal at weaning age, in some severely-affected animals, tremors persist into adult life [5]. Congenital tremors are often complicated with splayed hind legs [6]
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