Zika virus is transmitted by mosquitoes.  But mosquitoes also transmit other pathogens, such as malaria and parasitic nematodes.  This project set out to examine whether a relatively benign nematode infection common throughout Latin America – i.e., mansonelliasis – could enhance the transmission of Zika virus by mosquitoes.  Mansonelliasis is one of several diseases caused by a group of nematodes known collectively as filarial worms.  Filarial worms are vector-borne and parasitize all classes of vertebrates, except fish.  There are at least 6 different species that exclusively parasitize humans, including Mansonella ozzardi, the species that causes mansonelliasis in Latin America.  Adult females produce tiny larvae called “microfilariae” that enter the blood and skin of their host.  When ingested by mosquitoes, the microfilariae quickly penetrate the mosquito stomach and move to the thorax where they complete their development.  I speculated that if the same blood also contained Zika virus, then the virus could “hitch a ride” with  penetrating microfilariae and be transported directly into the body of the mosquito without having to first undergo replication in the mosquito stomach.  This would speed up virus development in the mosquito and make mosquitoes able to transmit the Zika virus much sooner than they normally would.  In effect, microfilarial infections could enhance Zika virus transmission.  Before beginning the work, all required compliance issues allowing me to produce Zika virus-infectious mosquitoes and obtain microfilaremic human blood from overseas had to be met.   After approvals were in place, successful laboratory infections of mosquitoes with Zika virus were accomplished in short order.  However, a major setback to the project occurred upon the unexpected and tragic death of my Trinidadian collaborator who was to be the source of Mansonella ozzardi infected blood.  This filarial species is not easy to obtain because it only grows in humans.  Thus the only way to get it is to collect blood from naturally-infected people in Latin America.  Attempts to find another source of this parasite species proved fruitless.  To keep the project going, I chose to use another species of filarial worm – i.e., Brugia pahangi – that can be obtained from an NIH-supported research repository known as BEI Resources.  When Brugia pahangi microfilariae were mixed with Zika virus and fed to mosquitoes, the virus moved into mosquito body cavities more rapidly and in greater proportion than in mosquitoes fed only virus.  Thus, the ability of B. pahangi microfilariae to “enhance” Zika virus infectivity to mosquitoes was confirmed.  To test if Zika virus interacted somehow with B. pahangi microfilariae, I incubated Zika virus with purified B. pahangi microfilariae for several hours, then subjected the microfilariae to extensive washing to the point where there should have been no virus left in the test tubes.  However, when miniscule amounts of the washed microfilariae were injected into mosquitoes, Zika virus was recovered a week later from 4 of 29 (14%) injected mosquitoes, indicating that Zika virus had indeed associated with B. pahangi microfilariae during co-incubation – i.e., Zika virus either stuck to the surface of microfilariae or was swallowed by the microfilariae.  In addition those studies, I also tested  the ability of our local mosquito species to transmit Zika virus.  I found that one of the most aggressive and abundant mosquito species in the northern hemisphere, Aedes vexans, was capable of becoming infected and transmitting Zika virus.  Although this study was somewhat ancillary to my investigation of the interaction of Zika virus with microfilariae, I felt it remained true to the larger goal of the NSF RAPID initiative – i.e., to better understand mosquito transmission of Zika virus.  The project provided excellent training in classic arbovirology techniques for two graduate students and three undergraduate students.  In summary, my students and I were able to show that microfilarial worms, when ingested together with Zika virus by mosquitoes, resulted in an enhanced infection of mosquitoes with Zika virus.  The worms made a difference.

Last Modified: 08/23/2018
Modified by: Jefferson A Vaughan