Skip to main content

The virus that rocked the Four Corners reemerges

Deer mice, like this, were eventually discovered to be the cause of the deadly virus in the Four Corners region, however other rodents across the country can also transmit it. (Image: CDC)

Nearly 20 years ago, an unknown, rapidly fatal disease broke out in the Four Corners area of the United States where the borders of Arizona, New Mexico, Colorado, and Utah meet. Had it not been for the fact that a young, otherwise healthy couple died within a week of each other of similar symptoms, this particular deadly virus might not have been discovered for quite some time.

In May 1993, a 19-year-old male marathon runner died just three days after being admitted to a New Mexico hospital for flu-like symptoms and shortness of breath. His fiancé had died of a similar unexplained respiratory illness only a few days earlier. This led the New Mexico Office of Medical Investigations to take a closer look at the Four Corners area, where within hours they discovered five more cases of young, otherwise-healthy individuals who had died of sudden respiratory failure.

When initial laboratory tests failed to identify the cause of the deaths, the Centers for Disease Control (CDC) was called in. The CDC in conjunction with the state health departments of three of the four states, the Indian Health Service, the Navajo Nation and the University of New Mexico joined forces to try to solve the mystery as well as identify other cases.

The evidence pointed to an unknown virus. Further research, including new methods of looking at the molecular structure, indicated it was a new strain of Hantavirus, one which is typically transmitted to humans by rodents. During the summer of 1993, almost 1,700 rodents of all types were trapped in and around the areas where the victims had lived and worked, in an effort to determine which type of rodent was the cause of the virus. Although several types of rodents were infected, deer mice were the most infected group.

The victims' households were compared with nearby "control" households to determine how the victims might have become infected. What researchers found was that there were more rodents in the victims' households compared to the control households, and also that the victims were more likely to thoroughly clean their homes and to plant, garden, or otherwise work with soil. In this outbreak, the virus killed 13 people — half of those it infected, for a disturbingly high mortality rate of 50%.

In November of 1993, the CDC and the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) independently isolated and grew the virus. The virus was eventually called Sin Nombre Virus (SNV), and the disease named Hantavirus Pulmonary Syndrome (HPS). To go from discovery of a new virus to isolation in a matter of only six months was quite extraordinary.

Once the virus was isolated, it was determined by examining tissue samples that the first known victim of HPS was actually a 38-year-old male victim in Utah in 1959. There were other isolated cases over the years that were also found to be HPS.

It was believed that the Four Corners outbreak occurred because the population of deer mice increased 10-fold from the previous year. The area had been subject to a drought for several years, but heavy snowmelt and spring rains in early 1993 provided a wealth of vegetation and plentiful food sources, leading to the rapid breeding of mice. An increase in mice meant a potential increase in contact with humans.

Although certain strains of the Hantavirus (particularly in South America) allow for person-to-person transmission, no Hantavirus in the United States has ever been found to be transmitted in this way. Transmission occurs by humans being bitten by an infected rodent, or, more commonly, by inhaling aerosolized virus particles from rodent excreta. The general fatality rate is 36%, and there is no cure, only medical intervention to treat the symptoms.

HPS is not isolated to the Four Corners area. It has been found in Florida (the "Black Creek Canal virus," linked to the cotton rat), Louisiana (the "Bayou virus," linked to the rice rat), and even New York ("New York-1 virus," linked to the white-footed mouse). In fact, it has been found in 34 states, although the majority of cases have been found in New Mexico, Colorado, Arizona and California.

In the summer of 2012, the largest outbreak of Hantavirus since 1993 occurred in Yosemite National Park. Ten people were infected, ranging in age from 12 to 56. Three of the victims died. The outbreak occurred in the Curry Village cabins, which have been closed since August. Rodent control measures have been undertaken, as well as measures to educate visitors and staff of the symptoms and potential dangers of the virus. The National Park Service publishes regular updates on its response to the Hantavirus in Yosemite.

Related Links:

Representative Image Caption
Deer mice, like this, were eventually discovered to be the cause of the deadly virus in the Four Corners region, however other rodents across the country can also transmit it. (Image: CDC)
Blog Name