Human illnesses are being transmitted to critically endangered mountain gorillas, putting these rare animals further at risk, new research shows.

Centuries ago, mountain gorillas (Gorilla beringei beringei) lived in relative isolation and were rarely seen by people. Today, they live in just two protected parks, where they are surrounded by human settlements in Rwanda, Uganda and the Democratic Republic of the Congo. Meanwhile, ecotourism provides the bulk of the funding needed to keep these critically endangered primates alive.

The rare species is at risk on multiple fronts, including poaching, slaughter by rebels, and now, human diseases.

According to a study published this week in Emerging Infectious Diseases, respiratory diseases have been on the rise in mountain gorilla populations in recent years. The diseases not only occur more frequently but also have become more severe, and they are now the number-two cause of mountain gorilla deaths.

Now, for the first time, researchers have shown that at least some of these respiratory illnesses are being transmitted to the gorillas by humans.

The study was initiated after a 2009 outbreak hit a gorilla family group in Rwanda. Twelve animals were infected, experiencing coughing, eye and nasal discharges and lethargy. A number of the gorillas were treated with antimicrobial drugs by the Mountain Gorilla Veterinary Project, but two untreated gorillas, an adult female and a three-day-old infant male, died from the infection. Prior to the deaths, the infant's mother was treated for her infection via remote delivery (darts). The adult female died before the veterinarians conducted their "clinical intervention."

Tissue analysis of the dead gorillas found the culprit: an RNA virus called human metapneumovirus (HMPV). The actual cause of death for the adult gorilla was bacterial pneumonia infection, but the paper says the HMPV infection "likely predisposed" her to pneumonia. Researchers found the infant's lungs showed signs of "pulmonary atelectasis, congestion, mild alveolar hemorrhage, and histiocytosis" as well as numerous other problems.

Analysis of the HMPV found in the gorillas linked it to the strain of the virus found in South Africa, although the exact source remains unknown.

In a prepared statement, one of the study's authors outlined how dangerous this situation could be for this endangered species: "Because there are fewer than 800 living mountain gorillas, each individual is critically important to the survival of their species," said Mike Cranfield, executive director of the Mountain Gorilla Veterinary Project and a wildlife veterinarian with the University of California, Davis. "But mountain gorillas are surrounded by people, and this discovery makes it clear that living in protected national parks is not a barrier to human diseases."

As with most well-managed endangered species, some care is taken to help prevent the spread of disease from human visitors. According to the paper, "The Rwandan, Ugandan, and Congolese governments restrict tourist numbers and proximity, and the Congolese wildlife authority mandates that masks be worn by persons visiting gorillas." But unfortunately, that may not be enough.


Photo via Wikimedia Commons