Transmission of Lyme Disease by Mosquitos and Flies


The classic bulls-eye rash is one that most people are warned to watch out for and are told to seek medical assistance if it appears on the skin. This rash is called erythema migrans and may occur from infection with a bacterium of the genus Borrelia. These bacteria are spirochetes and have a flagellum that aids in mobility. Borrelia burgdorferi is the most common species associated with Lyme disease. Although there are many subspecies that are closely related, only three definitively cause Lyme disease: B. burgdorferi sensu strictoB. afzelii, and B. garinii.

Lyme disease is commonly known to be transmitted from tick bites in North America, Europe, and Eurasia. However, research has shown that insects other than ticks can harbor the bacterium. Based on a study in Germany, it has been shown that Borreliacan survive in mosquitos from larval stages to adult stages without dying(1). Normally, Borrelia produces a protein that allows for its survival in a tick until the tick begins to feed and the bacteria can exit the tick into a new host. The bacteria are less likely to be able to survive in a mosquito’s gut due to chemical differences and gut composition. However, mosquitoes feed more often than ticks, therefore reducing the amount of time needed for the Borreliato survive before transmission to a new host.

Additionally, Borrelia was isolated from mosquitoes and horse flies in a study conducted in 1988 by Magnarelli and Anderson from the Department of Entomology in New Haven, Connecticut. The sources of infection for these insects were not identified in the study. However, it was inferred that the prevalence of Borrelia in these two other winged groups may be due to high concentrations of cattle, horses, and deer that were exposed to Lyme disease through tick bites. The local cattle and large mammals tested had antibodies to Lyme disease, but no spirochetes were isolated.
Although the study did not find a reservoir of infection, it did provide interesting data that showed Borrelia could survive in organisms besides ticks. In addition to larger mammals, mice in the area where the study was conducted were known to be infected with Borrelia and lends evidence that the area the research group sampled from had Borrelia in its sylvatic cycle. Mosquitoes and horseflies that suck blood regularly may have a higher chance of picking up and transmitting Borrelia from one or more infected hosts(2). The paper also cites that although anecdotal, there have been records of deer fly bites and the subsequent development of the erythema migrans rash.
Although there has not been conclusive evidence that mosquitoes and flies can transmit Lyme disease to humans, there have been particular anecdotal cases of transmission in addition to the evidence that Borrelia can survive within these organisms. It may be worthwhile for research organizations to conduct further studies that investigate this non-tick vector mode of transmission because Lyme Disease could be far more prevalent than once thought.
By Anna Klavins
R&D Microbiologist
HARDY DIAGNOSTICS
Sources:
(1)    Sponaugle, R. Lyme Study: How Borrelia Bacteria is Transmitted from Mosquitoes to Humans. Sponaugle Wellness Institute. 2016. https://sponauglewellness.com/lyme-study-how-borrelia-bacteria-is-transmitted-from-mosquitoes-to-humans/
(2)     Magnarelli, L.; Anderson, J. Ticks and Biting Insects Infected with the Etiologic Agent of Lyme Disease, Borrelia burgdorferi. Department of Entomology, The Connecticut Agricultural Experiment Station. New Haven, Connecticut. Journal of Clinical Microbiology; p 1482-1486. 1988.

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