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Study finds migrant workers at risk of hantavirus exposure

Migrant farm workers are the group most at risk of exposure to the hantavirus in southern New Mexico and the El Paso, Texas, area, a study led by New Mexico State University biochemist Colleen Jonsson suggests.

Jonsson and her colleagues took blood samples from 436 people to determine if people in southern New Mexico are exposed to the hantavirus at rates similar to those in the northern part of the state, where most cases of the often-fatal hantavirus illness have been reported. They also looked for differences between migrant farm workers and the general population.

The researchers found that the rate of exposure to the virus was similar -- just under 1 percent of the people tested had antibodies to the hantavirus, close to the exposure rates found in earlier studies in the Four Corners region. All of those who tested positive in Jonsson's study, however, were migrant farm workers.

"We can't be sure where these people were infected," Jonsson said. "This study alerts physicians to the possibility of hantavirus in migrant workers and it alerts migrant workers to the risks in their jobs."

Results of the study will be published in the journal Virus Research.

Jonsson, whose research focuses on the biochemistry of viruses such as the hantavirus and the AIDS virus, collaborated with NMSU graduate students and with pathologist Brian Hjelle of the University of New Mexico School of Medicine on the study. They worked with public health officials and student volunteers to collect blood samples from 436 people during 1996 and 1997, looking for antibodies that would be present in the blood only if the person had been exposed to the hantavirus.

The study included 115 people in Las Cruces; 114 in Columbus and Deming; 91 in Hatch, Derry and Arrey; and 116 in El Paso.

In El Paso, "we had to go at one o'clock in the morning to the Santa Fe Bridge," where migrant workers gather before traveling by bus to work in the fields of southern New Mexico, Jonsson said.

About 40 people, mostly student volunteers, were involved in the project, she said. Besides collecting blood samples, the researchers "did a lot of education and prevention," she said. "We handed out a lot of educational materials."

The hantavirus, which often causes a fatal respiratory illness, is believed to be transmitted to people who breathe dust particles contaminated with the urine or feces of infected rodents, especially deer mice. Although most of the New Mexico cases of the disease have occurred in the Four Corners area, rodents in the southern part of the state are known to carry the hantavirus, Jonsson said, noting that there are many different strains of the virus.

Studies had been done to determine the prevalence of exposure to the virus in northern New Mexico, but none had been done previously in the southern part of the state, Jonsson said.

Although a majority of the people included in the southern New Mexico sample were not migrant workers, none of the year- round community residents tested positive for hantavirus antibodies, she said. The three farm workers who did test positive -- two in the Deming-Columbus area and one from El Paso -- may have been exposed to the virus during such work activities as cleaning barns or working in grain sheds, she said.

The three positive blood samples represented 0.7 percent of the total. The overall exposure rate in the U.S. population is 0.2 percent, according to a National Health and Nutrition Study of 10,000 samples. A recent study in the Four Corners area found 1.0 percent of 192 samples taken at an Indian Health Service clinic to contain hantavirus antibodies.

The southern New Mexico study started as an honors thesis for NMSU graduate student Joy Brown, who is now doing a medical residency in San Diego, Jonsson said. NMSU doctoral student Liza Gonzalez, who has done research on the hantavirus in Paraguay, also participated in the study, and Elizabeth Lindsey of the NMSU Department of Communication Studies did the statistical analysis of the results.

Jonsson recently was awarded a $1.19 million federal grant to continue her research toward the development of therapeutics for the hantavirus. In addition, she and some of her colleagues are working toward the establishment of a Center for Emerging Pathogen Research at NMSU to focus on illness-causing organisms of rising concern in the border region, such as the hantavirus and drug-resistant forms of tuberculosis.

Karl Hill
Oct. 23, 2000