Location: Foreign Animal Disease Research
Title: The pathogenesis of highly virulent African Swine Fever virus infection in domestic pigs challenged by four distinct routes Authors
Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 16, 2013
Publication Date: N/A
Interpretive Summary: The purpose of this study was to compare methods of experimental infection for African Swine Fever (ASF) in order to determine which method is optimal for future research and vaccine development. Groups of pigs were infected with African Swine Fever virus via the upper gastrointestinal tract (intraoropharyngeal), the upper respiratory tract (intranasopharyngeal) and intramuscular routes or through direct contact exposure to infected pigs. Within the first three infection routes, pigs were given either a low, mid, or high dose of virus. Pigs infected via direct contact were exposed to sick pigs for 24, 48 or 72 hours. Among the routes, doses and exposure times, parameters such as clinical signs, the presence of virus within the blood and excretions collected from the tonsil and nasal cavity, as well as macroscopic and microscopic changes within tissues were examined and compared. Within all groups, animals that became infected had clinical signs and changes within tissues that were similar to previously described experimental and natural outbreaks of ASF. Differences amongst the percentage of animals infected per group and the onset and degree of virus within the blood and excretions suggest that the intranasopharyngeal route of infection is the most favorable method to be used for experimental research.
Technical Abstract: In order to optimize novel systems for African Swine Fever Virus (ASFV) vaccine development, domestic pigs were challenged with the highly virulent ASFV-Malawi strain via intraoropharyngeal (IOP), intranasopharyngeal (INP), intramuscular (IM), and direct contact (DC) routes. Direct challenge doses ranged from 10^2 – 10^6 50 percent hemadsorbing doses (HAD^50) whereas contact challenge varied from 24 – 72h of comingling with previously infected pigs. All challenge routes resulted in clinical progression and postmortem lesions similar to those previously described in association with experimental and natural infection. Onset of clinical signs occurred between 1-7 days post inoculation (dpi) characterized by pyrexia and obtundation with variable progression to hematochezia, melena, moribundity and death. Viremia was first detected between 4-5 dpi in all inoculation groups whereas ASFV shedding from the nasal cavity and tonsil was first detected at 3-9 dpi. Overall, IM and DC were the most consistent manners of challenge as reflected by a 100 percent incidence of infection under all exposure doses and times; however these routes suffer from unnatural challenge route (IM) and inability to control dose and timing of challenge (DC). INP inoculation resulted in a consistent progression of disease across a wide range of doses whilst preserving simulation of natural exposure and is therefore considered to be a superior system for pathogenesis and vaccine efficacy investigation.