When a mysterious and deadly illness began to sicken members of the Navajo community in the Four Corners region of the Southwestern U.S. in 1993, U.S. Centers for Disease Control and Prevention (CDC) investigators were stumped. However, the cause of the illness was less of a mystery to Navajo elders. Because officials were willing to listen to valuable insight gained from centuries of traditional knowledge, a virus that was previously unknown to infect humans in North America was identified as the source of the disease.
The Mysterious Outbreak
The Four Corners region of the U.S. derives its name from the intersection of 4 states: Colorado, New Mexico, Utah and Arizona. Situated on the Colorado Plateau, the area is known for its stunning natural features, like the Grand Canyon, Painted Desert and Zion National Park. A large portion of this region is within the 27,000 square miles (approximately 70,000 square kilometers) that make up the Navajo Nation.
Featured in countless films and TV shows, the landscape has a rugged and unique beauty that is synonymous with adventure and discovery. The Navajo people have lived in the region for around 1,000 years. Spanish missionaries, who arrived in the area much later, chose the name Navajo, but tribal members call themselves the Diné (the people).
In Spring 1993, this rugged landscape and its people became the focus of national attention after the death of a young Navajo man. He was a competitive marathon runner, and previously in very good health, traveling on a road trip with his family on the morning of May 14, 1993. Seemingly out of nowhere, the man became so severely short of breath that his family called for emergency care at a roadside gas station. By the time the emergency crew arrived, he was in full respiratory failure and later died in a nearby emergency department from florid pulmonary edema. The patient's history revealed that he was traveling to his fiancée's funeral when his severe symptoms began. She had also died from a sudden onset of respiratory edema. Investigators soon discovered more deaths with the same symptoms: fever and myalgia, followed by rapid decline and death within just a few days. Within an 8-week period, 10 people had died. Local officials had stumbled on an outbreak already in progress.
On May 28, New Mexico state health officials requested assistance from the CDC. The epidemiology team quickly narrowed the cause to 3 possibilities: a new, aggressive influenza virus; an environmental toxin or a previously unrecognized pathogen.
Sharing Navajo Knowledge
Indigenous knowledge offers a wealth of insight into the subtle patterns of the land. Passing stories from 1 generation to the next makes history extremely personal. In this way, knowledge becomes more than just the facts in a sequence. The listener gains ownership; it becomes their story as well. The Navajo, like other Native American tribes, have preserved their history and their culture in this way for centuries.
Diné elders and healers recognized a recurring pattern related to the ongoing respiratory outbreak in the Four Corners region. Similar outbreaks had occurred in 1918 and 1933, and there were records of others further back, predating bubonic plague in Europe. These previous outbreaks occurred following years of excess precipitation. The increased rainfall caused by the 1992-1993 El Niño phenomenon led to a bumper crop of pinyon pine nuts, an important food source for the local rodents. This abundant food supply resulted in a rodent population explosion. 
In Navajo tradition, humans and mice come from different worlds and, therefore, should be kept separate. Upsetting the balance with too much intermingling between species can bring on diseases, like what was seen in the Four Corners region. Elders warned their people to be careful of deer mice and prairie dogs, as contact with their waste could spread disease. They recommended burning contaminated clothing and sealing food to protect it from rodent access and contamination.
When CDC investigators met with tribal elders, they were informed of this regional history. One of the first important clues to the identity of the pathogen came from these meetings. Because investigators were willing to seek out local knowledge and take in the wisdom granted to them, they began to make real progress in identifying the mysterious illness.
Integrating International Expertise
The connection between the increased rodent population and outbreak timing was an important breakthrough for the CDC investigative team. Several members had international experience investigating similar cases in Europe and Asia. They noticed pathological similarities between cases observed in the current outbreak and some they had seen in the Eastern Hemisphere. In both European/Asian and Four Corners Region cases, infected individuals demonstrated intravascular fluid levels so depleted that hemoconcentration (increased concentration of blood cells) occurred, leading to elevated hemoglobin and hematocrit. This observation, combined with the knowledge gained from the Diné, led scientists to consider a previously unknown hantavirus as the culprit.
Before this time, hantavirus outbreaks in the Western Hemisphere had only ever been seen in rodents. Despite this and other discrepancies, such as lung-versus-kidney involvement, the team began an extensive rodent-trapping program to test their theory.
Genetic and antibody testing, along with detailed clinical and pathological examinations of more than 1,700 mice, revealed the source of the mysterious illness was, indeed, a previously unknown hantavirus.
The Culprit: Hantavirus
Hantaviruses are a family of viruses belonging to the Orthohantavirus genus and are responsible for severe diseases, including Hantavirus Pulmonary Syndrome (HPS) and Hemorrhagic Fever with Renal Syndrome (HFRS). While hantaviruses are found globally, those found in the Western Hemisphere, specifically North America, are known to cause HPS, while hantaviruses in Europe and Asia more commonly attack the kidneys and cause HFRS. Hantaviruses are spread through the aerosolization of virus particles in rodent waste, or by eating food contaminated with rodent bodily fluids. The hantaviruses found in the U.S. are not documented as transmissible between people. 
Initial symptoms of hantavirus infection are "flu-like," and include fever, headache and muscle pain. These usually begin within 3 weeks of exposure to the virus. In the U.S., severe cases will progress to HPS, which has a 40% mortality rate. Within 24 hours, most HPS patients will experience some amount of low blood pressure. Pulmonary edema and pleural effusion are common, and patients with cardiopulmonary symptoms begin to decline rapidly.
As there is no specific treatment for HPS, early detection and care are critical for successful intervention. Symptom management, such as fluid administration, intubation, ventilation, cardiac monitoring and support, are the only ways to manage severe disease progression. Without adequate care, death usually occurs within 24-48 hours of cardiopulmonary system involvement.
What's in a Name?
Now that the pathogen causing the 1993 HPS outbreak in the Southwestern U.S. had been identified as a novel hantavirus, scientists needed to name it. Standardized nomenclature helps to differentiate specific pathogenic strains or illnesses and facilitates collaboration for future research and treatment. In the past, it was a common practice to name a new pathogen or disease after a famous victim or location. Current guidelines for naming conventions from the World Health Organization (WHO) now discourage this practice. They recommend using generic names based on symptom and victim descriptions, and if the pathogen is known, it should be part of the name as well. Examples of this convention include coronavirus, severe fever with thrombocytopenia syndrome or amyotrophic lateral sclerosis.
Names based on a location or specific population can cause unintentional social, psychological and economic problems for the affected groups by provoking backlash against them. The Navajo experienced this during the 1993 outbreak when the media dubbed it the "Navajo disease." Vacation reservations were canceled, and major events were moved to other locations, dealing a heavy blow to an already fragile tribal economy. Racial stereotyping led to Navajo people being refused service at various businesses, and Navajo students were required to undergo medical testing to visit college campuses.
These experiences were fresh when the time came to name the new virus. In keeping with convention at the time, scientists wanted to name the new pathogen "Muerto Canyon hantavirus," after the discovery location. However, the Navajo tribe objected to using the name of a sacred place. The virus was renamed to "Four Corners virus." Fear of continued stigma meant that locals objected to that name as well. Thus, the virus that caused the HPS outbreak in 1993 is now known as the "Sin Nombre Virus," or the "virus without a name" in Spanish.
For the Diné, it is taboo to speak a loved one's name for 4 days after their death or to say anything negative about them, and silence is considered most respectful. Sin Nombre takes on a poetic meaning in this way. If stating a name gives something power to harm, then refusing to grant a name takes that power away.
The Gift of Knowledge
The Four Corners outbreak demonstrates the immense value of Indigenous knowledge. When lives are at stake, investigators need to use every available resource. The people who have lived with the land for generations may hold the answers to the source of the next emerging infectious disease or the next medical breakthrough. But only if scientists are willing to listen.
