Mosquito researchers track dengue fever in Sonora, Mexico

07/07/04



Students in a UA course on the insect biodiversity of Sonora check on a mosquito trap in Guaymas. Photo courtesy of UA Center for Insect Science.

Full size image available through Therese Markow, tmarkow@arl.arizona.edu.

Biologists from the University of Arizona in Tucson are teaming up with health officials from the Mexican state of Sonora to learn more about the mosquitoes that carry dengue and West Nile viruses and about the disease-causing organisms.

The reported number of dengue fever cases in Sonora has been increasing in the last several years, and the disease appears to be moving north. The dengue fever season in Sonora, the Mexican state just south of Arizona, is seasonal and peaks mid-October, after the summer rainy season.

The UA team will travel to Hermosillo, the capital of Sonora, July 15 and 16 to give public health officials a workshop on trapping and identifying various species of mosquitoes. The team will collect mosquitoes in Hermosillo, Guaymas and Navojoa.

Dengue fever is sometimes called "break-bone fever" because the disease is so painful. One form, dengue hemorrhagic fever, is fatal in about five percent of patients. Currently there is no vaccine against the disease.

"The way to look at it is, dengue is an enemy," said Therese Ann Markow, director of the UA Center for Insect Science and Regents' Professor of ecology and evolutionary biology. "The idea is to get to know your enemy well in order to know its weak spots."

Markow is collaborating with Sonoran health officials Dr. Francisco Javier Navarro Gálvez, director general of Servicios de Salud de la Comunidad (director of community health services), and Dr. J. Gerardo Mada Velez, director, Enfermedades Transmisibles por Vector y Zonosis (director of vector-borne diseases).

The newly formed UA-Mexican research collaboration will investigate the ecology, genetics and distribution of various mosquito species in Sonora and of the four types of dengue virus and its close relative, West Nile virus.

"The ecology, distribution and genetics of the mosquitoes and the viruses need to be studied simultaneously to understand how they interact to cause disease," Markow said.

Other UA members of the team are Michael Worobey, an assistant professor of ecology and evolutionary biology, Frank Ramberg, an assistant research scientist in the department of entomology, Sergio Castrezana, an ecology and evolutionary biology graduate student, and Joel Vergara, an entomology graduate student.

In May, Markow offered employees of the Servicios de Salud de Sonora (Sonora's public health agency) the opportunity to attend a UA course on the insect biodiversity of Sonora. She expected one or two people to come to learn about identifying insects and was astonished when 13 people showed up, eager to spend days staring at insects through microscopes.

As a result, she initiated this joint research project on disease-carrying mosquitoes and the viruses they transmit.

She said the Sonoran health department is keen to control and prevent the diseases but has limited expertise and resources in some areas.

"That's where we come in," she said. "We can provide training. The big things are how to identify the mosquito species that transmit the diseases and which molecular techniques can detect the viruses."

"Part of the problem is no one has done a mosquito inventory in the state of Sonora," Markow said. The UA/Mexico collaboration will remedy that by doing a complete survey of the species of mosquitoes in Sonora.

Project members will trap mosquitoes widely throughout Sonora, identify them and test them for the viruses.

In addition to testing the mosquitoes for dengue and West Nile viruses, the researchers will test blood collected from patients to identify which strains of the dengue virus caused the infections.

Sonora once had only two types of the dengue virus but now all four are found there. According to Worobey, that means people have an increased risk of getting dengue fever a second time because, although having one bout of dengue fever makes a person immune to the one type, the person is still susceptible to the other three.

It's only during the second infection with dengue virus that the person has about a five percent chance of developing the even nastier, hemorrhagic form of the disease. In dengue hemorrhagic fever, the person's blood vessels start to leak, causing bleeding from the nose and mouth. Of those people who get the hemorrhagic form of dengue, up to five percent will die, Worobey said.

Joaquin Ruiz, the dean of UA's College of Science, said, "Teri Markow's efforts, both in educating ecologists from Mexico as well as better understanding the transmission of these diseases, is important not only for Sonora but also for Arizona."

Markow and Ruiz will visit Mexico City in August to talk to representatives from the National University of Mexico and from Consejo Nacional De Ciencia Y Tecnologia (CONACyT), Mexico's federal agency to fund research in science and technology, about expanding the scope of the project within Sonora.

Source: Eurekalert & others

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