Captive western lowland gorillas proven susceptible to COVID-19

Today (January 12, 2021) it was announced that multiple western lowland gorillas at the San Diego Zoo and Safari Park (in Escondido, California) tested positive for SARS CoV-2, the virus that causes COVID-19. To date, no wild, human-habituated eastern gorilla has tested positive for coronavirus.

Scientific research conducted by Gorilla Doctors and collaborators has shown gorillas to be susceptible to human respiratory pathogens. Indeed, respiratory illness is the second leading cause of death in wild gorillas after trauma. When a gorilla exhibits clinical signs of respiratory illness, Gorilla Doctors is able to test for the presence of pathogens (virus, bacteria, parasites, etc.) by collecting fecal samples and running diagnostic tests to try and determine the underlying cause of illness.

Since the arrival of SARS CoV-2, the virus that causes COVID-19 disease, Gorilla Doctors has been operating under the assumption that gorillas are susceptible to the virus, and have expanded our testing to include detection of coronavirus. We are monitoring and testing for caronavirus as well as other known respiratory pathogens when a gorilla is sick. As stated above: to date no wild eastern gorilla has tested positive for SARS CoV-2.

Below we outline the steps taken by Gorilla Doctors and our park partners from first observation of signs of respiratory illness to pathogen detection using fecal samples in wild eastern gorillas. While the gold standard for detecting SARS CoV-2 is a mucosal (oral or nasal) swab, in wild gorillas this requires full immobilization (anesthesia), which is only performed in cases of extreme illness where more hands-on treatment is needed. Fecal sample collection is non-invasive and ideal for monitoring pathogens in wild populations. However, fecal samples are less reliable than mucosal swabs or saliva given the very nature of feces and the presence of multiple types of waste material, including other microorganisms. Therefore, the presence of a specific pathogen in a fecal sample, especially a respiratory virus, may be difficult to detect. That said, over many decades of field experience Gorilla Doctors has developed a working protocol that allows us to effectively monitor wild eastern gorillas for respiratory illness and the emergence of new pathogens.

Step 1: Identifying Clinical Signs of Respiratory Illness in a Wild Gorilla

Wild, human-habituated eastern gorillas are monitored daily by park staff. Gorilla Doctors provides regular training on how to identify clinical signs of illness or injury. When a tracker notices a gorilla with clinical signs of respiratory illness, they notify Gorilla Doctors. Gorilla Doctors then conducts a veterinary monitoring visit to observe the individual gorilla. Clinical signs may include: coughing, nasal discharge, lethargy and poor appetite. Once Gorilla Doctors confirms that the individual is experiencing a respiratory illness, Gorilla Doctors will collect a fresh fecal sample for testing.

Dr. Fred Nizeyimana conducts veterinary monitoring visit. Photo by Skyler Bishop for Gorilla Doctors

Step 2: Collecting a Fecal Sample from a Sick Gorilla

There are two ways to collect a fecal sample from a specific individual gorilla in a group. Very often before gorillas leave their night nests in the morning, they will defecate in the nest. If this behavior in a sick individual is directly observed, Gorilla Doctors can collect the fecal sample from the nest after the gorilla has departed. The second method is again through direct observation of the individual during the day and collecting a sample following defecation. In both cases, sample collection is non-invasive – there is no direct contact with the individual gorilla.

The sample is immediately mixed with a reagent that renders any possible pathogen in the sample inactive. There is no live virus once the fecal sample has been mixed with the reagent. [Note: Fecal samples in general tend to contain low quantities of a specific respiratory pathogen; this also makes it less likely for a respiratory pathogen to be transmitted via exposure to feces.]

While Gorilla Doctors waits for the sample to be tested, we continue active monitoring of the sick individual/s. In most cases, respiratory illness will resolve on its own. When it does not, Gorilla Doctors administers supportive medications (anti-inflammatories, antibiotics, vitamins) through an injection via dart (video below shows clip of a gorilla receiving medication via dart about 30 seconds in). If the illness progresses or the individual’s condition deteriorates, we consult with park authorities and discuss the possibility of a full immobilization using anesthesia to perform a physical exam, collect additional samples and provide further treatment to support recovery. Gorilla Doctors also closely monitors the entire gorilla group to watch for the transmission of the illness to other individuals in the group.

Step 3: Testing a Sample for the Presence of Pathogens

Samples are sent to a laboratory for testing. Testing of fecal samples requires additional steps to process the sample – first removing extra waste materials (e.g. undigested plant material) that could interfere with the detection of a specific pathogen. To test for the presence of a virus, we first use consensus PCR (cPCR, PCR = Polymerase Chain Reaction), to test at the level of the viral family. For example, SARS CoV-2 is a specific coronavirus that belongs to the family Coronaviridae.

cPCR is designed to cast a wide net and allow us to quickly determine the presence of a pathogen within a viral family. Should a sample test positive for coronavirus we can then conduct a second, more involved PCR test using specific primers. These primers are genetic tools that essentially act as “detectives” – when they are mixed with genetic material from a biological specimen they help search for and detect a specific virus in that specimen. Currently, we can also run the specific PCR protocol for SARS CoV-2.

Step 4: Receiving a Positive Test Result

In the case of wild, human-habituated eastern gorillas, receiving a positive test result for a specific pathogen can inform additional treatment and also identifies/confirms that a specific pathogen exists in the population.

Given the recent positive test for SARS CoV-2 in captive western lowland gorillas, we now have evidence that gorillas are indeed susceptible to the SARS CoV-2 virus. The mild respiratory illness exhibited by these positively-tested gorillas is our first evidence of how the virus might affect the health of gorillas but it is too soon to draw any conclusions regarding the severity of illness gorillas may experience. Our vigilance in best practice safety protocols and monitoring for signs of respiratory illness in wild eastern gorillas remains as critical as ever. Prevention is always better than mitigation.

Read the San Diego Zoo and Safari Park Announcement

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