African Swine Fever Virus load in hematophagous dipterans collected in
outbreaks from Romania: risk factors and implications
Abstract
African swine fever (ASF) is a highly contagious viral disease of suids
that causes significant economic damage. The summer peaks and river
courses have triggered the hypothesis that vectors may be involved in
the transmission of the virus. The aim of our study was to evaluate the
risk factors associated with the presence of ASFV DNA in hematophagous
dipterans and to analyze the relevance of Ct values of the positive
samples in ASF outbreaks in Romania, as an indication for the viral
load. The current study included 99 pools of stable flies (
Stomoxys calcitrans) and 278 pools of biting midges (
Culicoides spp.), collected in June-September 2020, from 30
outbreaks of ASF in domestic swine from backyard farms (BF), type A
farms (TAF) and commercial farms (CF). All extracted DNA was tested for
the presence of ASFV genome using a real-time PCR protocol. Ct values of
39.53 and below were considered as positive. The blood meal source was
identified in the hematophagous insects by using a PCR protocol
targeting the mitochondrial gene cytochrome c oxidase subunit 1. Data
were analyzed using R software v. 4.0.5. In total, 2978 insects (
S. calcitrans n= 198 and Culicoides n=2780) were collected
in 19 outbreaks out of the 30 sampled farms. Ten species of biting
midges were identified. The total number of insect pools showed
significant differences according to the month of sampling, with a
higher number of pools collected in August and September. Overall, 137
pools out of the 377 examined were positive for the presence of ASFV
DNA. There was a higher viral DNA load in farms where pigs were present
at the moment of sampling compared to farms where pigs were already
culled, in S. calcitrans compared to Culicoides spp. and
in CF and TAF compared to BF.