Systematic Epidemiological Investigations of Cases of Senecavirus A in US Swine Breeding Herds

Abstract

Epidemiological investigations were conducted on a case series of six Senecavirus A (SVA)-affected breeding herds in the United States to determine potential routes of introduction and enhance the swine industry's knowledge of SVA's clinical presentation and spread. Each SVA-affected herd was evaluated using a standard form to ensure that all relevant data were collected. The form was used to guide a detailed discussion about the clinical presentation of SVA and risk events that occurred in the 4 weeks prior to the first observation of clinical signs with the herd veterinarian and farm personnel. Each event was then subjectively assigned a risk level of low, medium or high likelihood for SVA introduction by the investigation team. The clinical presentation of SVA varied by case. All SVA-affected herds (six of six) reported increases in pre-weaning mortality and sow anorexia. Vesicular lesions were observed in four of six herds, and mild-to-moderate neonatal diarrhoea was observed in three of six herds. No gross anatomic or histologic lesions were observed in neonatal pigs that tested positive for SVA via PCR. Multiple potential routes of introduction were identified. Events subjectively rated as high risk for SVA introduction were on-farm employee entry (six of six), carcass disposal (four of six), cull sow removal (three of six) and breeding replacement entry (two of six). Non-swine domestic animals, rodents, other visitors, repairs outside swine barns, feed delivery, weaned pig removal and semen entry were assigned a high risk level in one of six herds. Cases occurred in breeding herds of all sizes with variable biosecurity in both swine dense and swine sparse areas.

Update on Senecavirus Infection in Pigs

“…The morbidity and mortality rates of senecavirus-induced disease vary according to the affected pig category. In a herd that is affected for the first time, the morbidity rates range from 4 to 70% depending on the clinical signs and the pig age groups [ 20 , 23 , 33 , 34 , 37 ]. Senecavirus outbreaks presented morbidity rates of 0.5 to 5% in weaned pigs and 5 to 30% in finishing pigs and breeders [ 2 , 20 , 34 ], which varied according to the geographical region and the herd origin.…”

“…Senecavirus outbreaks presented morbidity rates of 0.5 to 5% in weaned pigs and 5 to 30% in finishing pigs and breeders [ 2 , 20 , 34 ], which varied according to the geographical region and the herd origin. Remarkably higher morbidity rates in sows were reported, reaching 70 to 90% [ 37 ]. However, the mortality in these categories is very low (≈0.2%), with pigs recovering soon after the remission of clinical signs that last for 10 to 15 days.…”

Senecavirus A: An emerging pathogen causing vesicular disease in pigs

“…The presence of viral RNA and infectious particles was found in the lungs, the mediastinal and mesenteric lymph nodes, the liver, the spleen, the small and large intestines and the tonsils during the acute phase of disease (12). In newborn pigs, morbidity and mortality rates are considerably higher, especially in one-to four-day-old piglets, with morbidity rates of up to 70% and the mortality rates from 15% to 30% (1,5,15,28). At post-mortem examination, a significant percentage (5-27%) of piglets with diarrhoea showed subcutaneous or mesenteric oedema, and most piglets had milk in the stomach.…”

“…The introduction of SVA can be prevented by adopting strict biosecurity measures. The entry of vehicles, equipment, people, animals and food into pig production facilities must be strictly controlled (1,13). Livestock trailers and carcass-removal equipment were subjectively assessed as the most likely routes of SVA introduction in a risk-assessment study (1).…”

“…The entry of vehicles, equipment, people, animals and food into pig production facilities must be strictly controlled (1,13). Livestock trailers and carcass-removal equipment were subjectively assessed as the most likely routes of SVA introduction in a risk-assessment study (1). Preferably, pigs should be transported by vehicles or livestock trailers that have not been in contact with vehicles, personnel or animals from Senecavirus-positive herds.…”