Writes for Wildlife

celebration and protection of the natural world

Category: Conservation

Zoonoses, Emerging Infectious Diseases and Wildlife

Zoonoses are infectious diseases that can be transmitted between humans and animal species. The infectious agent may be a bacteria, virus, fungus, protozoa or helminth. Zoonoses may be transmitted directly, indirectly or be vector-borne (e.g. via an insect bite). Humans have lived in close contact with animal species for thousands of years, and so while zoonoses are not a new phenomenon, they are receiving more focus recently because of the role they are playing in emerging infectious diseases.

Most emerging infectious diseases (EIDs) are zoonotic pathogens. In fact since the 1940s more than three hundred human diseases have emerged from animals, and of the pathogens which affect humans, the majority (61%) are zoonotic. Many of the zoonoses have reservoirs of infection within wildlife populations. A reservoir of infection is often a group or species of animals which can carry and possibly transmit organisms infectious to humans, without displaying symptoms of disease. (Taylor et al. 2001) EIDs are receiving attention because of the negative impact on human and animal health, with potential associated economic consequences. They may affect farm animal health and welfare as well as wildlife conservation efforts.

The role of wildlife in zoonoses is multifaceted. Anthropogenic factors are driving major changes of wildlife habitats. The increasing global human population and the associated requirement for food, shelter and fresh water creates more opportunities for wildlife interaction and therefore infection.

Climate change and global warming provide conditions where pathogens may be able to exploit a new geographic niche or host species. Most microorganisms have optimum temperature ranges, and environmental changes can lead to alterations in transmission, environmental persistence, or virulence. The consequences of these changes are not always predictable. (Bengis et al. 2004) In countries where water is a limited commodity, water sources can become a location for direct and indirect infection of humans by the wildlife species with which they share this essential resource.

Direct destruction of habitats by humans, means that the wildlife residents are required to relocate, learn new foraging behaviour, or rely on novel food species, all of which creates potential conflict and interactions with humans.

One devastating example of the interconnectedness of wildlife, humans, livestock and disease, and the importance of forests for human health, occurred in Malaysia in the late 90s. Slashing and burning of vast swathes of tropical rainforest provide land for pig farming. The fruit bats who had been displaced from the forest, were forced to forage for fruit on the trees near the pig farms. Pigs ate the pieces of fruit contaminated with bat saliva and urine which fell into their enclosures. The pigs ingested the Nipah virus, which is carried asymptomatically and shed by the bats, and developed severe respiratory and neurological symptoms. For many pigs the first symptom was sudden death. The Pig farming industry collapsed at a massive financial loss to the farmers and the Malaysian economy. In addition to this there were hundreds of humans infected by the virus and more than one hundred people lost their lives. (Aguirre et al. 2012, Kahn, 2011) However, there needs to be caution in the response to identifying the source of infection or the reservoir species. Bats for example, provide many essential ecosystem roles including pollination, insect consumption and seed dispersal; they should not be thought of as primarily a source of infection.

As the human population increases, some communities employ varied means of finding food. In some countries of the world this means that bush meat is being hunted, traded and eaten on a regular basis. Currently over 500 million wild animals each year. Not only is this a threat to several iconic and critically endangered species, but the opportunities for human infection arising from the contact with and consumption of infected animals is increasing. Ebola virus causes a haemorrhagic disease of both humans and great apes; and with no specific treatment, mortality rates in both groups can be high.  (Bermejo, et al. 2006) HIV is also thought to have entered the human population via bushmeat consumption. (Bengis et al. 2004)

Wildlife trade is also big business, with live animals or animal products shipping round the globe. Millions of birds and fish are transported live each year, as well as tens of thousands of primates and reptiles. The trade is estimated to be worth $6 billion. The increase in intensive farming means that an outbreak of disease in a single species can be devastating.

As well as being a source, wildlife can be adversely affected by zoonotic diseases. The impact on human health of Ebola, Rabies, and HIV, which are all zoonotic pathogens, cannot be underestimated as they cause significant morbidity and mortality. However, Humans are also able to infect vulnerable wildlife species. Gorilla tourism in Africa has become a popular way to raise funds to support conservation of this critically endangered species. However Gorilla are susceptible to pathogens any human visitors may be carrying, particularly respiratory viruses. Gorilla have also sustained marked losses due to the recent Ebola outbreaks. (Bermejo, et al. 2006)

Examples of zoonotic diseases – Many pathogens can affect human, livestock and wildlife health. (Image adapted from: GAO analysis of USGS data, 2011)

 

Travel to almost everywhere on the globe is possible; the world is increasingly connected. This means that pathogens, diseased people and animals may also move around with relative ease, meaning that infectious diseases can be difficult to contain or to then trace to a source when an epidemic is under way. A concerted, multidisciplinary, global effort is required to reduce the impact of zoonotic diseases worldwide. There must be collaboration between human health professionals, ecologists, animal health professionals, as well as other involved parties to try to predict, monitor and document diseases. The role that biodiversity plays, in maintaining health cannot be overlooked, and I plan to cover these topics further in future posts.

 

 

References

Aguirre, A., Daszak, P. & Ostfeld, R. (2012). New directions in conservation medicine applied cases of ecological health. Oxford ; New York: Oxford University Press

Bengis RG, Leighton FA, Fischer JR, Artois M, Mörner T, Tate CM. (2004) The role of wildlife in emerging and re-emerging zoonoses. Rev Sci Tech. Aug;23(2):497-511.

Bermejo M., Rodríguez-Teijeiro, J., Illera G., Barroso, A. Vilà, C. Walsh, P. (2006) Ebola Outbreak Killed 5000 Gorillas. Science: Vol. 314, Issue 5805, pp. 1564 DOI: 10.1126/science.1133105

GAO analysis of USGS data (2011)  https://www.gao.gov/assets/590/586047.pdf

Kahn, LH, (2011) https://thebulletin.org/2011/02/deforestation-and-emerging-diseases/

Taylor LH, Latham SM, Woolhouse ME, Risk factors for human disease emergence. Philos Trans R Soc Lond B Biol Sci. 2001 Jul 29;356(1411):983-9. https://doi.org/10.1098/rstb.2001.0888

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Scotland’s Red Squirrels

During spring, red squirrels are focussed on producing and nurturing young. The benefits to us are that there are numerous observable behaviours that can hint that the red squirrels in your area are breeding, even if catching a glimpse of the tiny kits themselves proves difficult. To find out more about red squirrel breeding behaviours, read my article on the Saving Scotland’s Red Squirrels blog.

 

A red squirrel feeding at RSPB Loch Leven earlier this year

Red Squirrels have been declining in Scotland for decades. This native species has struggled with disease and competition from grey squirrels (a non-native species, introduced in the late 1800s) resulting in a vastly diminished red squirrel population. Scotland is home to around 75% of the UK red squirrels, and the Saving Scotland’s Red Squirrels project aims to bolster, conserve and increase the numbers of this iconic species.

There has been some encouraging news for Scotland’s reds recently.  Population decline has slowed and project showed that the numbers in 2017 remained stable. If you spot any red or grey squirrels you can report your sightings which will support this important red squirrel conservation work.

Antarctic Ocean Sanctuary

As the snow in the UK finally melts and we get back to our normal activities, it might be an opportune moment to turn our attentions outward again, beyond our personal environmental challenges, and think globally.

The ‘Beast from the East’ created conditions in Central Scotland not unlike those in Antarctica…

Antarctica is a land of snow and ice and strong winds, but it is also home to a myriad of species and provides important climate services for the earth.

There are no people native to Antarctica, and most of the current residents carry out scientific research. Antarctica belongs to no single country or group and it follows that everyone has a responsibility to safeguard this unique environment. Antarctica is still relatively free from the detrimental effects of human activity, but only creation of an Antarcic Ocean Sanctuary will ensure that this wilderness purity endures.

We still have barely scratched the surface of the species diversity of the Antarctic Ocean. Some resident species have never been observed by a living person. As I mentioned in my conservation medicine post, biodiversity is vital for the health of humans and the planet. Scientists who study this area are amazed by the variety. It is certain that large scale fishing activity or mineral explorations will significantly harm this important ecosystem and research indicates that Antarctic ecosystems take years to recover from damage.

Greenpeace have been integral to protecting the landmass of Antarctica, but there is more that needs to be done to keep this truly pristine wilderness safe from anthropomorphic degradation. Many of the key species that we are familiar with, such as penguins, rely heavily on the health of the surrounding waters as they are ocean hunters. Vast quantities of krill make these oceans an important feeding ground. Krill are vitally important to the food web at all levels, and are the main food source of several whale species which visit these waters.  Seismic blasting, drilling and other mineral prospecting activity adversely affects the natural behaviours of wildlife species. Industrial fishing activities in these waters could have numerous detrimental effects including accidental bycatch, and damage to the sea floor.

The UK government can influence the creation of an Antarctic Ocean Sanctuary in the waters around Antarctica, as they are part of the Antarctic Ocean Commission. The proposed sanctuary is I.8 million square miles (five times the size of Germany). If you would like to be part of creating the biggest ocean sanctuary in the world you can sign the petition here.

If you would like to be entertained by David Harbour (of Stranger Things fame) dancing with the Antarctic penguins on a recent trip with Greenpeace to promote this campaign then by all means click here and enjoy.

 

 

 

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