Preliminary analysis of whether mosquitoes can carry and transmit African swine fever

African Swine Fever Virus Load in Hematophagous Dipterans Collected in an Outbreak from Romania: Risk Factors and Implications

African swine fever (ASF) is a contagious viral disease of swine 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. In temperate climates, insect numbers increase in the late summer. Low temperatures and frosts decrease the number of active insects. Their presence is strongly associated with the nearby wetlands or swamps around the farms. 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 obtained following RT-PCR analysis 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 296 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 the ASFV genome using a real-time PCR protocol. Ct values of 39.53 and below were considered as positive (min: 18.19; median: 31.41; max: 39.53). 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, 3,158 insects (S. calcitrans n = 198 and Culicoides n = 2960) were collected in 23 farms of the 30 outbreak 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 395 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.

What Is the Real Influence of Climatic and Environmental Factors in the Outbreaks of African Swine Fever?

Simple Summary

African Swine fever is present on the African, European and Asian continents, causing devastating economic impact due to the mandatory mass depopulation in confirmed outbreaks. Using the data reported by the Romanian National Sanitary Veterinary and Food Safety Authority, we created a database with all the localities from Romania where the outbreaks were confirmed between 2020 and 2021 as well as the geoclimatic features of those areas. The database was then used to statistically analyze the frequency of confirmed outbreaks in relation with specific climatic and environmental factors. Our results show that such studies need to be continued in order to have a better understanding of the geoclimatic risk factors in the transmission of African swine fever virus.

Abstract

African swine fever has a significant economic, social and environmental impact due to official regulation of the disease, namely the mass depopulation of all pigs in confirmed outbreaks. The main objective of the present study was to statistically analyze the possible correlation between the number of outbreaks and infected pigs from backyard farms with the altitude, seasonal average annual humidity, and average temperature during spring, summer, autumn and winter, as well as the distance from forests, rivers, and lakes in Romania. The study included all infected backyard pigs with African swine fever virus (n = 7764) and outbreaks (n = 404) that occurred in Romania between 6 February 2020 and 2 March 2021. The number of infected pigs and ASF outbreaks were significantly higher in localities at altitudes between 100 and 500 m, average annual humidity between 60% and 80%, average spring temperature between 10 and 14 °C, average summer temperature between 16 and 22 °C, average autumn temperature between 10 and 13 °C, average winter temperatures between −1 and 2 °C, and at distances of less than 5 km from the forests, less than 15 km from lakes and less than 5 km from the rivers. The number of affected pigs decreased significantly at summer temperatures below 16 °C.