More than just birds and mosquitoes could play a key role in the spread of West Nile virus (WNV). Scientists recently determined that an uninfected mosquito can get WNV from an infected mosquito when feeding directly next to it on an uninfected mouse. The findings mean the transmission of WNV might be more complex than previously thought; mammals previously considered “dead-end hosts” and those that don’t get WNV infection actually might serve as an avenue for more rapid amplification of the virus.

Stephen Higgs, BSc, PhD, FRES, is editor-in-chief of Vector-Borne and Zoonotic Diseases and associate professor in the Department of Pathology at the University of Texas Medical Branch. He and colleagues performed the non-viremic transmission study in collaboration with a researcher in Oxford, England. In non-viremic transmission, arthropod vectors (such as mosquitoes) become infected with a pathogen before it can multiply or appear in the bloodstream of the host on which the vectors are feeding.

When a mosquito feeds on WNV-positive blood, it picks up a certain amount of virus and the virus level then briefly drops before multiplying in the mosquito’s gut and spreading to its salivary glands. Within seven days of the blood meal, many mosquitoes are capable of infecting a susceptible victim, and within 14 days of infection, almost every susceptible mosquito can serve as a WNV vector.

Higgs says, “Our traditional idea was that in order to become infected, the mosquito needs to feed on a vertebrate host that has the virus in its blood, and that there has to be a certain amount in the blood before the mosquito can become infected” and serve as a vector. Skipping this mosquito-bird-mosquito pattern greatly condenses the virus’ life cycle