Researchers make discoveries on West Nile virus, monkeypox, and yellow fever

Researchers from the University of Texas Medical Branch at Galveston present significant new discoveries on West Nile virus, monkeypox, and yellow fever in four papers in the September issue of Emerging Infectious Diseases, published by the Centers for Disease Control and Prevention. The articles are summarized below, and can be found on the EID web site.

In “Year-Round West Nile Virus Activity, Gulf Coast Region, Texas and Louisiana,” West Nile authority Dr. Robert Tesh and colleagues from UTMB and the Harris County and Galveston County mosquito control offices present the first hard evidence that West Nile virus continues to circulate during winter along the Texas and Louisiana Gulf Coasts. This finding is important to understanding how the virus spreads when mosquito populations increase in the spring, both on the Gulf Coast and farther north where migrating birds can carry West Nile great distances.

Tesh and his colleagues describe a possible new model for studying infections by monkeypox, a relative of the deadly smallpox virus, in “Experimental Infection of Ground Squirrels (Spermophilus tridecemlineatus) with Monkeypox Virus.” Although smallpox has been eradicated from the wild and under treaty is preserved only at a high-security CDC lab in Atlanta and a similar center in Russia, biodefense experts fear other samples of the virus may exist that could pose a grave threat to world health if they fell into the wrong hands, especially since smallpox vaccination is no longer common. Monkeypox affects monkeys in much the same way that smallpox affects humans; it can be used as a substitute for smallpox virus in studies that could lead to treatments for its much more dangerous relative. The discovery that it produces a similar disease in ground squirrels and that these rodents can be employed in experiments instead of monkeys should make such work substantially easier.

UTMB researchers Dr. Stephen Higgs and Dr. Alan Barrett examine the dangers yellow fever still poses for Bolivian cities in “Yellow Fever Virus Infectivity for Bolivian Aedes aegypti Mosquitoes,” testing the idea that the urban areas of Bolivia have been protected from yellow fever outbreaks because the mosquitoes that live there cannot transmit the virus. Laboratory experiments, they report, show that mosquitoes collected in Santa Cruz, Bolivia in 2001 are quite effective at transmitting yellow fever virus—leaving open the question of why yellow fever outbreaks have not occurred there and in other Bolivian urban areas in recent years.

Yellow fever is still a significant public health problem throughout Latin America, despite the existence of an effective vaccine. In “Genetic Divergence and Dispersal of Yellow Fever Virus, Brazil,” scientists from UTMB and the Instituto Evandro Chagras in Belém, Brazil, present a genetic analysis of 79 yellow fever virus samples taken in Brazil between 1935 and 2001, using it to track the development and dispersion of different strains of the virus. The data, they say, suggest that migration of infected people could be an important factor in virus dispersal. Unexpectedly, they also found that virus taken from a patient who died of yellow fever in 1975 was actually a vaccine strain, adding weight to recently raised concerns about adverse effects from use of the 17DD yellow fever vaccine, particularly in patients with weakened immune systems.