A Review of African Swine Fever and the Potential for Introduction into the United States and the Possibility of Subsequent Establishment in Feral Swine and Native Ticks

Abstract

African swine fever (ASF) is caused by African swine fever virus (ASFV), which can cause substantial morbidity and mortality events in swine. The virus can be transmitted via direct and indirect contacts with infected swine, their products, or competent vector species, especially Ornithodoros ticks. Africa and much of Eastern Europe are endemic for ASF; a viral introduction to countries that are currently ASF free could have severe economic consequences due to the loss of production from infected animals and the trade restrictions that would likely be imposed as a result of an outbreak. We identified vulnerabilities that could lead to ASFV introduction or persistence in the United States or other ASF-free regions. Both legal and illegal movements of live animals, as well as the importation of animal products, byproducts, and animal feed, pose a risk of virus introduction. Each route is described, and current regulations designed to prevent ASFV and other pathogens from entering the United States are outlined. Furthermore, existing ASFV research gaps are highlighted. Laboratory experiments to evaluate multiple species of Ornithodoros ticks that have yet to be characterized would be useful to understand vector competence, host preferences, and distribution of competent soft tick vectors in relation to high pig production areas as well as regions with high feral swine (wild boar or similar) densities. Knowledge relative to antigenic viral proteins that contribute to host response and determination of immune mechanisms that lead to protection are foundational in the quest for a vaccine. Finally, sampling of illegally imported and confiscated wild suid products for ASFV could shed light on the types of products being imported and provide a more informed perspective relative to the risk of ASFV importation.

Ecological drivers of African swine fever virus persistence in wild boar populations: Insight for control

“…Understanding mechanisms by which pathogens transmit between hosts is key for defining disease risk and for planning effective control strategies. In addition to direct host‐to‐host or vector‐borne transmission, pathogens can spread through environmental sources, such as through contact with fomites (Allerson, Cardpna, & Torremorell, ), ingestion of contaminated drinking water (Breban, ; Kraay et al, ), contact with contaminated soil (Turner et al, ), contact with contaminated carcasses (Chenais, Ståhl, Guberti, & Depner, ), or carcass scavenging (Brown & Bevins, ; Wille et al, ). Environmental sources of infection can promote pathogen persistence by increasing their likelihood of contact with susceptible hosts because many pathogens can remain viable in the environment longer than they can keep a host infectious.…”

Ecological drivers of African swine fever virus persistence in wild boar populations: insight for control

“…Understanding mechanisms by which pathogens transmit between hosts is key for defining disease risk and for planning effective control strategies. In addition to direct host-to-host or vector-borne transmission, pathogens can spread through environmental sources, such as through contact with fomites (Allerson et al 2013), ingestion of contaminated drinking water (Breban et al 2013, Kraay et al 2018), contact with contaminated soil (Turner et al 2014), contact with contaminated carcasses (Chenais et al 2018), or carcass scavenging (Wille et al 2016, Brown and Bevins 2018). Environmental sources of infection can promote pathogen persistence by increasing their likelihood of contact with susceptible hosts because many pathogens can remain viable in the environment longer than they can keep a host infectious.…”

Quantifying the dynamics of pig movements improves targeted disease surveillance and control plans

“…Therefore, there is a need to capture movements between commercial and noncommercial pig 362 farms and vice-versa. Gathering this information becomes more important as the pig industry 363 around the world prepares for the introduction of ASF, which will require tracking animal 364 movements among all pig farms (Brown and Bevins, 2018;Jurado et al, 2018). 365…”