Identification of a Divergent Lineage Porcine Pestivirus in Nursing Piglets with Congenital Tremors and Reproduction of Disease following Experimental Inoculation

Abstract

Congenital tremors is a sporadic disease of neonatal pigs characterized by action-related repetitive myoclonus. A majority of outbreaks of congenital tremors have been attributed to an unidentified virus. The objectives of this project were to 1) detect potential pathogen(s) in samples from piglets with congenital tremors and 2) develop an infection model to reproduce disease. Using next-generation sequencing, a divergent lineage pestivirus was detected in piglets with congenital tremors. The virus was originally most closely related to a bat pestivirus but is now more closely related to a recently published novel porcine pestivirus provisionally named atypical porcine pestivirus. A quantitative real-time PCR detected the virus in samples from neonatal piglets with congenital tremors from two separate farms, but not in samples from unaffected piglets from the same farm. To fulfill the second objective, pregnant sows were inoculated with either serum containing the pestivirus or PBS (control) by intravenous and intranasal routes simultaneously with direct inoculation of fetal amniotic vesicles by ultrasound-guided surgical technique. Inoculations were performed at either 45 or 62 days of gestation. All sows inoculated with the novel pestivirus farrowed piglets affected with congenital tremors while PBS-inoculated control piglets were unaffected. Tremor severity for each piglet was scored from videos taken 0, 1 and 2 days post-farrowing. Tremor severity remained relatively constant from 0 to 2 days post-farrowing for a majority of piglets. The prevalence of congenital tremors in pestivirus-inoculated litters ranged from 57% (4 out of 7 affected piglets) to 100% (10 out of 10 affected piglets). The virus was consistently detected by PCR in tissues from piglets with congenital tremors but was not detected in control piglets. Samples positive by PCR in greater than 90% of piglets sampled included brainstem (37 out of 41), mesenteric lymph node (37 out of 41), tracheobronchial lymph node (37 out of 41), and whole blood (19 out of 20). Although the first description of congenital tremors was in 1922, this is the first reported reproduction of congenital tremors following experimental inoculation with a divergent lineage porcine pestivirus. Studies investigating disease mechanism, epidemiology, and diagnostic assay development are needed to better understand the pathophysiology of congenital tremors due to this pestivirus.

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

“…The two affected litters showed some piglets with moderate to severe clinical signs of disease, a majority of piglets with mild clinical signs and even some with no clinical signs, similar to what we observe at farms with outbreaks. Our findings are in agreement with the findings by Arruda et al, who experimentally infected fetuses [15], whereas we infected pregnant gilts. Arruda et al [15] also observed large variation in the severity of clinical signs within affected litters.…”

“…All 99 samples (100%) from piglets with disease sampled at 10 different farms were PCR-positive, whereas only six of 66 (9%) of the controls without clinical signs were positive. This strong association was also found by Arruda et al [15]: 15/16 serum samples of congenital tremor piglets PCR-positive, four controls negative; and Postel et al [24]: 6/6 congenital tremor serum sample positive, 2/2 controls PCR-negative.…”

“…Soon thereafter, a link with congenital tremor type A-II was suggested by Arruda et al [15] and Postel et al [24]. The frequent detection and the large genetic variation of the virus in the Netherlands and Spain, in addition to the USA [15,16] and Germany [24,25], shows that APPV has probably spread worldwide. We measured a very strong association with congenital tremor.…”

“…Very recently it has been shown that a novel porcine pestivirus is likely involved in type A-II congenital tremor [15]. This novel pestivirus has been first described by Hause et al [16]: atypical porcine pestivirus (APPV).…”

“…This novel pestivirus has been first described by Hause et al [16]: atypical porcine pestivirus (APPV). Arruda et al [15] inoculated the virus in pregnant sows and the fetal amniotic vesicles of these sows. The sows did not get infected by APPV, yet the birth of piglets with congenital tremor after APPV inoculation in the amniotic fluid provided a strong indication that congenital tremor type A-II is caused by APPV [15].…”