The federal Centers for Disease Control and Prevention (CDC) in Atlanta have enlisted Sevilleta LTER scientists to assist in identifying the ecological relationships of the recent epidemic of Hantavirus-associated Adult Respiratory Distress Syndrome (HARDS) in the Southwest. The newly-identified disease, which has resulted in 14 deaths since its discovery in early May, is caused by a previously-unknown species of Hantavirus (family Bunyaviridae).
Hantaviruses comprise the virus group responsible for hemorrhagic fever in Asia, Europe, and South America. This new disease causes severe and rapid respiratory collapse, rather than the usual kidney malfunctions associated with hemorrhagic fever. As with other Hantaviruses, the virus appears to be transmitted by rodents, specifically the deer mouse (Peromyscus maniculatus). As of early August, of 55 suspected cases a total of 20 have been positively confirmed to be associated with the newly- discovered Hantavirus; 28 are still under investigation. Originally thought to be restricted to the Four Corners region of New Mexico, Colorado, Arizona, and Utah, the disease has now appeared across New Mexico, and into eastern Texas, Nevada and California. The mortality rate for the disease is currently 60 to 70 %.
In view of the rodent connection with this disease, medical investigators and public health officials were in need of ecological information on the deer mouse and other native rodent species. Anecdotal information from residents in the afflicted areas suggested that rodents were exceptionally abundant over the winter of 1992-93, and officials speculated that, if true, the increased potential for rodent-human contact and disease transmission might account for the sudden epidemic.
Biologists with the Sevilleta LTER and Canyonlands National Park were the only two groups having long-term data on rodent communities in the region. At the request of the CDC and the New Mexico Health Department, LTER researchers James Brunt, Doug Moore, and Bob Parmenter, with the assistance of NSF-REU student Sarah Ernest, provided detailed demographic analyses from 1989-1993 for the 22 rodent species inhabiting the area.
The LTER and National Park Service data showed tenfold population increases in various Pevmyscus species and wood rats (Neotorna spp.) during the spring of 1993. Population increases occurred simultaneously in grasslands, desert shrub lands, and woodlands. Comparisons of the rodent data to the region’s climatological data indicated that the rodent population dynamics were positively associated with the 1992 El Niño and the above-average precipitation during the winter of 1992-93. Parmenter presented the Sevilleta’s findings in mid-July at a Hantavirus conference at the CDC
Headquarters in Atlanta.
The LTER Program will also contribute to the as yet unanswered question: Is this a “newly evolved” virus, or has it actually been in the region for years? The Sevilleta LTER routinely collects museum specimens of rodents from all of its study sites. Under the direction of co-principal investigator Terry Yates (Curator of Mammals, University of New Mexico Museum of Southwestern Biology), LTER field crews collect tissue samples (heart, liver, bone marrow) and blood katyotypes (chromosomal complement of an individual or species) from rodent specimens each year, which are then preserved in ultra-cold freezers at UNM. Once the Hantavirus RNA has been completely sequenced and identified at CDC, virus researchers will then examine the stored LTER tissues to determine if the virus has indeed been present, though undetected, in the region’s rodent populations.
Historically, hemorrhagic fever epidemics in Asia and Europe show dramatic infection increases in autumn, following rodent invasion of houses with the onset of winter and the harvesting of agricultural crops. A similar scenario may await the Southwest, if rodent populations remain high. The results of the LTER analyses are being used to develop rodent/virus sampling strategies and disease prevention plans for human populations. Predictive relationships are being employed to ascertain the likelihood of a sustained population outbreak for the rodents in New Mexico, and to estimate the effectiveness of possible control measures to reduce human-rodent contact. These predictions, along with continued up-to-date measurements of rodent populations at the Sevilleta LTER sites, will contribute insights and direction to the strategies and contingency plans developed by the region’s public health officials to battle the HARDS epidemic.