With the current outbreak of Covid-19 occurring across the globe and the rumours that it started from the illegal meat trade in Wuhan, China has prompted more thought into how these diseases spread from animal to human and how to help prevent this. However, it also begs the question that should we be doing something to stop the return spread of disease from us, humans, to animal populations. Particularly those already at risk of extinction or declining populations.
Orangutan with infant - Sabah, Borneo
With the human population reaching 7.8 this year (2020) and a global range with highly efficient transport link between major population hubs it is easy to see why disease can spread so quickly. This high number of individuals also offers a large base for with diseases to evolve within. We see on a regular basis that pathogens in different area of the globe which cause the same disease can different significantly in their genetic make-up. An obvious example of this is drug resistance. Mycobacterium tuberculosis the casuistic agent of tuberculosis has acquired antibiotic resistance in many areas of the globe and certain strains are nearly untreatable, it’s these acquired or mutated genes that can cause problems.
What is causing a human pathogen from mutating to infect a domestic animal with a large range such as a domestic cat or one that has the potential to interact with its own species in the wild such a racing pigeon? Not much. We have seen the reverse happen on a number of occasions. H7N9 - otherwise known as avian flu - has spread from wild birds to humans and has caused the world health organisation (WHO) massive headaches or H1N1, commonly known as swine flu again caused similar concern.
So we have seen this occur in animal populations we are familiar with, but it is from animals with large populations and high human interactions. It is also animal to human transmission. But has it occurred the other way around? This is very hard to test for. Animals of course can’t communicate with a GP in the same way a sick patient might, and their health is monitored primarily by their carer and this is if it is a domestic animal. They might be part of a herd living outside in the elements and many diseases show similar symptoms. Certain symptoms might also just prompt increases in antibiotic doses – but what if the carer can’t afford that or the vet bills? Will the disease be left to spread or the animal killed? Those concerns are for domestic animals which can be slaughtered and bred again so their perceived value may be low and risk of spread might be restricted.
What if those animals the disease has spread to are wild animals? The concerns for monitoring are great but also control is very limited. Wild animals have a range, they interact with other wild animals of all species, they openly defecate along game trails where other animals will walk, it might be part of a pack or herd of family troop, the opportunities for a spread of a pathogen is enormous. But think again, what if this animal was critically endangered? Surely there wouldn’t be a risk of a human pathogen spreading to a critically endangered animal population, but there is and it has happened before.
Orangutan - Sabah, Borneo
Ebola is a word that rings alarm bells in everyone’s ears. The Ebola outbreak of 2014-2016 was the largest and most complex the world had seen. Initially believed to have spread from animals such as fruit bats, porcupines and non-human primates it quickly spread through the west African human population with a case fatality of 50%. It was devastating to human life in the area. However, a key point there is non-human primates. We are very similar to our primate family members in our genetic make-up. We share a lot of the same proteins and metabolites as our monkey pals. This means that very little often has to change in our pathogens so that they suddenly become their pathogens too. There have been reports that in the shadow of each human outbreak of Ebola there have been carcases of chimpanzees and gorillas in the neighbouring forests. In the early 2000’s (2002,2003) there was an Ebola outbreak in the gorilla population of Congo decimated the population there reducing its numbers by up to 95% - one paper reports 5000 gorilla’s killed. This species of Ebola virus (ZEBOV) is known to cause disease in humans and apes alike. It is often suspected that outbreaks start where the territory of apes and humans meet often starting from ape carcases. At the moment there isn’t evidence to suggest the Ebola virus that killed this number of gorillas came directly from a human population or whether it was a mutation within the ape population but it begs the question, why are we allowing this to happen?
It is very difficult to control interactions between humans and wild animals in a forest environment where there are known bushmeat trades and endemic populations living within great ape territories. We could argue that education is the key to advice against contact but this is challenging in people who are reliant on meat for a living. However, there are things that can be done. There are centres around the world that tolerate or even encourage close contact between humans and endangered animals. My recent trip to Borneo demonstrated this perfectly. There are centres that are doing fantastic things for the orangutans with aiding their re-introduction into the wild, with the aim to do so in the territory from which they were rescued, removing the worry about introducing non-endemic genes in an artificial way and allowing only trained staff and medical teams to interact with the animals. However, there are also centres which are tolerating direct human-primate contact with the general public. This is a major concern as people are traveling from all corners of the world to these centres, these people haven’t undergone rigorous health screening before contact is allowed and there is often feeding of human food – I say human because it isn’t food the animal would find in the wild – pathogens and contaminants would easily be transmitted across. How many of these tourists have acquired airplane flu from the air conditioning? How many have asymptomatic infection such as latent Tb (this is prevalent in 25% of the human population)? Some places will ask you to move away from the animals but it isn’t enforced, there are signs up telling people not to get close or feed but again this isn’t enforced... many of the animals at these centres do have the freedom to roam wild as well but are habituated to human contact which historically has kept many animals safe but now this barrier is broken down. If a fatal pathogen gets into one of these wild roaming endangered animals it could wreak havoc in the local population. These populations typically have reduced genetic diversity which is a key correlate for protection against these types of disease epidemics. The greater the genetic diversity the high chance of survival the population will have. But each successive disease outbreak can reduce this in an already limited population.
Orangutan Sheltering from the Rain - Sabah, Borneo
For the sake of these species we are trying to save, so much effort has gone in by so many people that for a single transferred pathogen that can cause fatal disease in one of these species can set back the conservation efforts of decades. It is definitely up to us, the consumer to determine whether the ‘zoo’ or ‘rescue centre’ we are visiting is genuine and really doing what is best for the animals. With the highly popular Netflix series ‘tiger king’ just aired showing the GW zoo claiming to be a rescue centre when it is obviously a breeding centre for privately owned big cats, it brings this topic to the forefront of the publics attention once again.