May 31, 2020

Coronavirus: Fewer Infections among High Altitude Peoples

New research published in the journal Respiratory Physiology & Neurobiology has suggested that peoples who are native to extremely high altitude climates may be less prone to infection and the effects of coronavirus. Such peoples included are the Tibetans living in the Himalayas, who have reported a much lower infection rate than the rest of China. The study also found that people in La Paz (capital of Bolivia and the highest capital in the world) are also reporting significantly fewer infections than their counterparts in the department of Santa Cruz (located a few hundred metres above sea level). Although the scientists have warned that the pattern of lower infection rates may not last, they are intrigued by the findings and are starting to focus on the relationship between the virus and altitude. Specifically, the researchers suggest factors including the people living at high altitudes' ability to cope with Hypoxia, dry mountain air, and high levels of UV radiation could all be playing a part in protecting high altitude communities from the virus. 

Below is an article by the Washington Post 

When tourists from Mexico, China and Britain became the first covid-19 fatalities in Cusco, Peru, it seemed as if the onetime capital of the Inca Empire might be headed for a significant outbreak.

Nestled in a picturesque Andean valley, the high-altitude city of 420,000 residents, the gateway to the cloud forest citadel of Machu Picchu, receives more than 3 million international visitors per year — many from pandemic hot spots, including the United States, Italy and Spain.

Yet since those three deaths, between March 23 and April 3, at the start of Peru’s strict national lockdown, there has not been another covid-19 fatality in the entire Cusco region, even as the disease has claimed more than 4,000 lives nationally.

Infections have also remained low. Just 1,062 of Peru’s 164,000 cases come from the Cusco region, meaning its contagion rate is more than 80 percent below the national average.

The relative dearth of cases and deaths in the internationally connected but high-elevation region has prompted speculation here that the novel coronavirus gets soroche, the Quechua word for altitude sickness.

Similar results have been seen elsewhere in the Andes, and in Tibet.

Scientists warn that the apparent pattern might not last, but the as-yet-unexplained phenomenon has them intrigued. Researchers are starting to investigate a possible relationship between the coronavirus and altitude.

In one peer-reviewed study, published in the journal Respiratory Physiology & Neurobiology, researchers from Australia, Bolivia, Canada and Switzerland looking at epidemiological data from Bolivia, Ecuador and Tibet found that populations living above 3,000 meters (9,842 feet) reported significantly lower levels of confirmed infections than their lowland counterparts.

They found that Tibet’s infection rate was “drastically” lower than that of lowland China, the rate in the Bolivian Andes was one-third that of the rest of Bolivia, and the rate in the Ecuadoran Andes was one-fourth that of the rest of Ecuador.

Ecuador has suffered one of Latin America’s worst outbreaks, with more than 39,000 reported cases and more than 3,300 deaths, according to official figures. But it has been centered on the Pacific port of Guayaquil. Bolivia’s 9,982 cases have been concentrated in the department of Santa Cruz, a few hundred feet above sea level. But the department of La Paz, home to the world’s highest capital, has had 507 cases.

The researchers hypothesize that populations living at high altitudes might be benefiting from a combination of an ability to cope with hypoxia (low levels of oxygen in the blood) and a natural environment hostile to the virus — including dry mountain air, high levels of UV radiation and the possibility that lower barometric pressure reduces the virus’s ability to linger in the air.

Other experts question the role of the environmental factors, noting that most coronavirus infections occur indoors, making UV levels irrelevant. But they are calling for more research into high-altitude populations’ response to the coronavirus, including the possibility that when infected, they sicken less and are therefore less likely to seek medical treatment or testing.

“The virus likes people. It doesn’t care about altitude,” says Peter Chin-Hong, who studies infectious diseases at the University of California at San Francisco. “But we’re still learning so much about this disease, and this does provide us with some good clues to try and understand its progression.”

Just three populations in the world have been found to have genetic adaptations to altitude: Himalayans, Ethiopian highlanders and Andeans. Yet Clayton Cowl, a pulmonologist at the Mayo Clinic and a former president of the American College of Chest Physicians, suspects the trend may be more closely related to acclimatization, the body’s ability to adjust temporarily to altitude, than to DNA.

That could explain why the coronavirus is raging on Peru’s Pacific coast, particularly Lima, where most residents descend from Andean ancestors, while the country’s mountain communities have thus far at least avoided the worst.

Cowl notes that prolonged exposure to altitude triggers a chain reaction in the lungs involving a protein known as ACE2 that might prevent pulmonary shunting, a problem common among covid-19 patients.

Ordinarily, when a part of the lung is damaged, the body redirects the flow of blood toward healthier areas that are better able to absorb oxygen. Shunting stops that process of redirection, resulting in hypoxia. It is, according to Cowl, a common element among the roughly 30 percent of covid-19 patients who exhibit mild symptoms yet have unusually low levels of oxygen in their blood — and who sometimes take a sudden turn for the worse.

But any benefits from altitude in coping with a coronavirus infection, Chin-Hong and Cowl said, would come only with full acclimatization, a process that typically takes three months. They both stressed that anyone suffering a coronavirus infection who traveled to a mountain area would normally see their symptoms worsen.

“Otherwise, we could treat them with a hyperbaric chamber,” Cowl said.

“From an epidemiological perspective, it is hard to know what this means. There’s likely to be a variety of factors, but it is truly interesting.”


Photo: A dog watches over La Paz from El Alto, Bolivia. (Aizar Raldes/AFP/Getty Images)