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AnimalsEndangered SpeciesScience

Human Virus Linked to Deaths of Two Mountain Gorillas

'silverback' (male) mountain gorilla

A form of human metapneumovirus (HMPV) has been identified as the likely cause of death in two mountain gorillas, an infant and adult female, following an outbreak of respiratory disease that hit Rwanda in 2009.

This is according to an April 2011 research study, by Palacios et al, published in the CDC’s journal Emerging Infectious Diseases. Quoting the authors:  “We report conclusive evidence for association of a human virus with death in mountain gorillas.”

An unknown number of other gorillas may be carrying the virus. Due to the genetic compatibility of humans and gorillas, wildlife biologists have long feared and predicted the spread of human diseases into this critically endangered population.  Now, it appears, their worst fears may have come true.

Less than 800 mountain gorillas (Gorilla beringei beringei) live entirely within two wildlife parks, encompassed by the Democratic Republic of the Congo, Rwanda, and Uganda. Formerly, the main threats to the gorillas’ survival came from the usual suspects:  poaching, killings by rebel soldiers, and habitat encroachment.

But over the past few decades, a new threat has emerged.

In general, what keeps this secretive primate species hanging on in the survival game is, primarily, revenue from ecotourism. Without this money to pay for law enforcement, monitoring and scientific study, these great apes would surely have been wiped out by poachers, settlers and rebel soldiers decades ago. However, there is also a not-so-beneficial flip-side to this year-round intrusion of admiring tourists: disease contagion (from humans to gorillas). It is estimated that 75% of the population is habituated to humans, meaning that they are so used to us that they no longer run away.

Gorilla Mother and Baby in Volcanoes National Park,  Rwanda
Gorilla Mother and Baby in Volcanoes National Park, Rwanda

According to a three decade long study of mountain gorillas from the Virunga Volcanoes region in Rwanda (Mudakikwa et al), infectious diseases (mostly respiratory) are now second only to trauma in causing sudden death amongst mountain gorillas — accounting for 1 in 5 gorilla death of this kind.

This risk of inter-species transmission of disease has been recognized for sometime. To prevent/minimize this risk, the governments of the three African nations restrict tourist numbers and proximity, and the Congolese wildlife authority mandates that masks be worn by persons visiting gorillas. Despite these measures, the frequency and severity of respiratory illness outbreaks has increased in at least four groups of gorillas from the Virunga Massif. All of the groups were “accustomed to tourism”.

Previous “experimental infections” of cynomologus macaques with HMPV showed only “minimal to mild” symptoms. However, in some primates, HMPV can cause a predisposition to several forms of bacterial pneumonia. This is believed to be the case with the one adult female gorilla noted in the study. The infant gorilla also show signs of respiratory illness , but which were confined to the lungs, whereas the female’s infection was more widespread throughout her body (including the kidneys).

toddler mountain gorilla
A toddler mountain gorilla

The researchers note their assertion that HMPV can be fatal to gorillas is supported by an earlier report of a respiratory outbreak amongst wild chimpanzees (all “human-habituated”) in Western Tanzania, causing the death of several of the apes.

Strains of the virus were recently discovered and described in South African primate populations. The source of the virus is unknown. Responding to critics that might assert the animals became infected during intervention (to treat another illness/injury), the authors of the study note that no vets or park personnel handled the apes during  their illness, stating:

“Although HMPV transmission as a result of human intervention to treat sick animals in the group is possible, it does not explain HMPV in the adult female, which died early in the outbreak before any clinical interventions were conducted.”

The mountain gorilla is, on average, the largest of all gorillas. Though terrestrial and quadrupedal, the ape will climb trees on occasion (if the branches can support its weight) and is capable of bipedal locomotion for up to 20 foot (6.6 meter) spurts. It is primarily an herbivore but will sometimes eat small invertebrates (insects). Its thick fur protects it from the colder temperatures of its preferred mountain habitat.

To protect this critically endangered animal, the authors advocate increased surveillance and monitoring of gorilla habitat (especially areas where human-gorilla contact is maximized, or new, due to conflict). In summation, the authors state:

“Although human proximity to mountain gorillas is essential for their conservation, also crucial is minimizing the risk for human-to–great ape transmission of respiratory pathogens.”

Read the entire report here: Human Metapneumovirus Infection in Wild Moutain Gorillas, Rwanda

For more information about what you can do to help protect mountain gorillas, visit: Mountain Gorilla Conservation Fund

Top image: d_proffer ; CC – By 2.0 (adult male “silverback” mountain gorilla)

Second image: Sarel Kromer ; CC – By – SA 2.0 (Gorilla Mother and Baby in Volcanoes National Park,  Rwanda)

Third image: KMRA ; CC – By 2.5 (a toddler mountain gorilla)




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