Do mosquitoes spread Lyme disease?

The myth that other insects could possibly spread Lyme disease stems from a study from Germany that evaluated the presence of Lyme spirochetes in mosquitoes. From this study came the patient-culture myth that you could get Lyme disease from mosquito bites.

Mosquitoes, lice and other insects have a different way of digesting their blood meal compared to ticks. When an insect ingests the spirochetes that cause Lyme disease they will be killed in the midgut because insects other than ticks have a different acidity and use proteases, certain digestive enzymes, to digest their meal. The midgut of other insects is hostile to the Lyme spirochete.

Relapsing fever spirochetes can be transmitted by lice. In contrast with Lyme spirochetes they are able to survive the harsh environment of the midgut of lice but relapsing fever is a different disease.

Transmission cycle

A fair amount of studies report the presence of Lyme spirochetes in mosquitoes and most studies found that between 1-3% of the mosquitoes indeed carried the Lyme spirochete. However, the presence of a spirochete in a mosquito doesn’t mean they are able to transmit it to humans. It is not so simple.

When Lyme spirochetes are ingested by ticks they adapt to the new environment by changing their outer surface proteins (osp-A) and remain immobile while the tick molds into the next developmental stage. When the tick feeds in the next stage the dormant spirochetes reactivate. The spirochetes start changing their outer surface proteins again to adapt to a vertebrate host, leave the midgut and disseminate into the saliva glands. From the saliva glands they are inoculated into the skin of the host. These developmental changes in the spirochete take approximately 2 days to complete. Far longer than a mosquito feeds.

Because of this low attachment and feeding time of the mosquito they are unlikely to ingest many Lyme spirochetes and they cannot be transmitted from the mosquito to the host because the mosquito is attached for only 90 seconds which is not long enough to transmit Lyme spirochetes. This is confirmed in studies that also failed to show the ability of mosquitoes to transmit Lyme spirochetes to vertebrate hosts.

Feeding Mechanism

Mosquitoes also feed from vessels and cannulate dermal capilaries and rarely draw blood from the interstitial tissue. The destruction of skin by tick feeding facilitates the uptake of Lyme spirochetes whereas the cannulation of capilaries by mosquitoes does not.

Tick saliva

Besides that mosquitoes do not meet the complex transmission requirements of Lyme spirochetes, ticks secrete saliva into the host. The components of this saliva assists the spirochetes within the new host. Other insects don’t need this protein in their saliva because they feed in a much shorter time and thus don’t have to temporarily shut down the inflammation response around the bite site. Without the assistance of these components of the tick saliva, Lyme spirochetes would be unable to infect a host.

No case reports

There are no case reports of patients that develop an erythema migrans after a mosquito bite in the literature.

Conclusion

It seems unlikely that mosquitoes can transmit Lyme disease.

Some mosquitoes transmit viruses and parasites like Malaria. If you are visiting endemic area for these diseases protect yourself and get the required travel vaccinations. If you develop an erythema migrans, visit a doctor. It might mean that you have overlooked a tick bite.

References