Are Insects Ebola's Natural Host/Reservoir?

Are Insects Ebola's Natural Reservoir?

Evidence Supporting Insects as the Vector
- Arthropods were around all of the outbreak sites.
- A single replication study conducted during the late 1970s suggested that Marburg virus (a relative of Ebola) could replicated in Aedes (Stegomyia) aegypti mosquitoes after intrathoracic inoculation (4).
- A case of Marburg Hemorrhagic Fever (MHF) in Zimbabwe coincided with a lesion "compatible with a horsefly or spider bite" (5).
Image from Monath (2)
Evidence Against Insects as the Vector
- Studies of insects found at the outbreak sites have failed to isolate Ebola in an insect (1). However, specimens were not collected at the beginning of the outbreaks, and during the first Ebola Sudan outbreak, DDT was sprayed around the hospital and the surrounding area (2, 3).
- Recent studies to ascertain whether Ebola repilicates in A. aegypti have failed to reproduce the result of the Kunz study (4, 6). However, the recent study did not use the strains of Ebola, Ebola Cote d'Ivoire, Ebola Sudan and Ebola Zaire, that are the causative agents of the outbreaks.
Unresolved Issues
- Only a small fraction of of the specimens collected have actually been tested for Ebola (2).
- Insects that were present at the beginning of the outbreaks have yet to be collected and analyzed.
- The reservoir insect could be a seasonal insect and not be present when insect species are collected for analysis
- A particular type insect could be an intermediate host and not the natural reservoir, or another organism could be the intermediate host obtaining Ebola from a particular insect species.

References:

Breman, Joel, et al. "A Search for Ebola Virus in Animals in the Democratic Republic of the Congo: Ecologic, Virologic, and Serologic Surveys, 1979-1980." Journal of Infectious Diseases. 1999;179(Suppl 1):S139-47.
Monath, Thomas. "Ecology of Marburg and Ebola Viruses: Speculations and Directions for Future Research." Journal of Infectious Diseases. 1999;179(Suppl 1):S127-38.
Lolik, Pacifico. "Containment and Surveillance of the Ebola Virus Epidemic in Southern Sudan." Ebola Virus Haemorrhagic Fever. Berlin: Elsevier/North-Holland Biomedical Press. 1978.
Kunz, C. et al. "Die vermehrung des "Marburg-Virus" in Aedes aegypt. Zentralbl Bakteriol I Orig 1968; 208:347-9.
Conrad J.L. et al. "Epidemiological investigations of Marburg virus diseases, southern Africa, 1975. American Journal of Tropical Medicine and Hygiene 1978; 27:1210-5.
Turrell MJ et al. "Lack of virus replication in arthropods after intrathoracic inoculation of Ebola Reston virus. American Journal of Tropical Medicine and Hygiene 1996;55:89-90.

©1999 Tara Waterman