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Enema infusion technique inappropriate for evaluating viral competence of ticks
M J Turell1, R J Pollack, A Spielman
1Virology Division, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011, USA.
Abstract:
To determine whether anal infusion of virus simulates the natural route of infection rather than intracoelomic injection, we compared the course of Venezuelan equine encephalitis (VEE) virus infection in Amblyomma cajennense (F.) ticks that had been exposed to virus by enema infusion with that in ticks fed on a viremic host or exposed by intracoelomic inoculation. Although virus was detected in virtually all ticks 14 d after exposure, orally exposed ticks contained significantly less virus (10(1.9) plaque-forming units [PFU] per tick) than did ticks infected by enema (10(4.1) PFU per tick) or intracoelomically (10(4.2) PFU per tick). At 42 d after virus exposure, only 1% of 512 orally exposed ticks contained virus, but most enema (77%, n = 43) or intracoelomically (79%, n = 29) exposed ticks were infected. Replication of VEE virus in A. cajennense ticks exposed to virus by enema infusion, therefore, appeared more similar to that of ticks inoculated intracoelomically than to those exposed orally. Thus, because enema infusion may bypass potential midgut infection and escape barriers, this procedure may not be appropriate for determining vector competence in ixodid ticks.
Insights
Anal infusion of Venezuelan equine encephalitis (VEE) virus in ticks does not simulate natural infection routes. This enema method bypasses midgut barriers, making it unsuitable for assessing tick vector competence.
Area of Science:
- Arthropod-borne diseases
- Virology
- Entomology
Background:
- Understanding tick-borne virus transmission is crucial for public health.
- Ixodid ticks are important vectors for various pathogens.
- Accurate methods for studying virus infection in ticks are essential for vector competence studies.
Purpose of the Study:
- To compare Venezuelan equine encephalitis (VEE) virus infection dynamics in Amblyomma cajennense ticks using different exposure routes.
- To evaluate if anal virus infusion accurately mimics natural tick infection pathways.
- To determine the suitability of anal infusion for assessing VEE virus vector competence in ticks.
Main Methods:
- Amblyomma cajennense ticks were exposed to VEE virus via anal infusion, intracoelomic inoculation, or feeding on a viremic host.
- Viral loads were quantified using plaque-forming units (PFU) at 14 and 42 days post-exposure.
- Infection prevalence was assessed at 42 days post-exposure.
Main Results:
- Ticks exposed via anal infusion or intracoelomic inoculation showed significantly higher viral loads at 14 days compared to orally exposed ticks.
- At 42 days, anal infusion and intracoelomic inoculation resulted in high infection prevalence (77% and 79%, respectively), while oral exposure showed very low prevalence (1%).
- Virus replication following anal infusion closely resembled intracoelomic inoculation, not oral exposure.
Conclusions:
- Anal infusion of VEE virus in A. cajennense ticks does not replicate natural oral infection routes.
- The enema method likely bypasses midgut barriers, leading to artificial infection dynamics.
- Anal infusion is not an appropriate method for determining vector competence in ixodid ticks for VEE virus.