Atypical Porcine Pestivirus: A Possible Cause of Congenital Tremor Type A‐II in Newborn Piglets

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.

An emerging novel virus: Atypical porcine pestivirus (APPV)

“…In comparison, CT are commonly caused by infectious agents including mild CSFV strain (Type A‐I) and previously unidentified causative agent (Type A‐II). The CT type A‐II is characterized with its sporadic and occasional occurrence in gilt litters, demyelination of the spinal cord and brain in piglets, and low‐moderate mortality of piglets caused by malnutrition . The clinical signs of CT type A‐II could be reproduced on the piglets, farrowed by sows infected with inoculum containing the potential agent 40 years ago, which has provided a powerful evidence to support the assumption that an infectious agent may be responsible for the tremor.…”

“…Pestiviruses, such as CSFV and BVDV have been detected in the boar and bull semens . APPV was detected in the preputial fluids and in the semen of 15% boars, which shows that the disease may be transmitted sexually . In the United States and Europe, the semens were collected from the “healthy” boars without a clinical history of CT.…”

“…CT is the phenomenon of “shaker pigs” or “dancing pigs,” which is characterized with clinical signs of muscular tremor and incapability of standing and feeding on sow's milk in newborn piglets . Severely affected piglets may die later because of inadequate colostrum intake and starvation.…”

“…Referring to the differences in the clinical signs, causes of diseases, and mortality, CT is divided into types A and B . Based on distinct causes of diseases, the type A is further subdivided into five subgroups (types A‐I, II, III, IV, and V) . The types A‐III and IV occur rarely, caused by inherited factors including a sex‐linked inherited defect in Landrace pigs (Type A‐III) and an inherited recessive genetic defect in Saddleback pigs (Type A‐IV), while another type is caused by exposure of specific toxins to the pregnant sows (type A‐V).…”

“…Of these, APPV was first identified by next‐generation sequencing from the samples in the United States in 2015 . Shortly thereafter, it was reported in pigs with CT in the United States, Germany, the Netherlands, Spain, Austria, China, and Brazil (Table ) …”