United in One Health (featured image).
(Source images: pixabay and adapted from mndh)

The concept of One Health ultimately sets its agenda on transcending the apparent borders between mankind, the animal kingdom, and the ecosystem to implement a cross-sectoral approach to prevent and manage health risks.

Taken each pillar individually, cooperation is not uncommon. For instance, trees share resources and send warning signals with the help of belowground fungal networks; meerkats collaborate by way of an elaborate vocal communication system to give their companions a heads up about lurking predators; and even people are able to lend their fellow human beings a hand, as demonstrated by the Living Cities collaborative.

But what we, humans, do not excel in is living sustainably with both our natural environment and our animal peers. For one, climate change is a telling example. The invention of the automated slaughter line for the processing of chicken meat is another expressive illustration.

And it should be self-evident by now that our interconnected nature is not a trivial fact: The SARS-CoV-2 virus is the latest powerful reminder of how fragile and important the relationship between ecosystem, animals, and humans actually is.

What I wish to do in this article is laying bare how the three components of One Health — animal, human, and environment — impact one another based on the discussion of the case study of Japanese encephalitis.

Multidisciplinary Kitchen

Concretely, putting an all-encompassing philosophy of health into practice means finding ways for veterinarians, physicians, environmental and wildlife health practitioners, and social scientists and health workers to collaborate and align their professional compasses.

Other than human collaboration, it also means tackling global health issues by coalescing working methodologies and insights from the three One Health subdivisions into one integrated approach.

Why such a concerted undertaking across a plethora of work fields can prove useful is best epitomized by the words of veterinarian Adam Little: “Compartmentalization of knowledge inhibits progress. In essence, this means that only by collaborative efforts can we properly analyze and address the complex, multi-faceted health problems that society faces today”.

Dozens of initiatives, programmes, legislation proposals, policies, and research papers are contributing to optimize this cross-departmental exercise. To name just a few, there is the One Health Initiative, a European One Health Action Plan against Antimicrobial Resistance, a joint master degree from Massey University (New Zealand) in the field of epidemiology and biosecurity that puts a special focus on zoonotic diseases, the One Health Network in South Asia, and the Netherlands Centre for One Health.

Let us now see how all of this plays out for one particular health problem.

Making the Case for a United Strategy towards Japanese Encephalitis

Japanese encephalitis (JE) is a viral encephalitis — inflammation of the brain — caused by a flavivirus, i.e. an animal virus of the family Flaviviridae, which also includes the Zika virus, the dengue virus, and the yellow fever virus.

JE is predominately present in Southeast Asia, and 87% of the reported human cases between 2011 and 2015 were traced back to India, Nepal, China, and Vietnam. What is more, mostly children and young adolescents run the risk of contracting JE, making it the lead cause of viral childhood encephalitis in Asia.

Geographical regions of risk in Southeast Asia for the case of Japanese encephalitis.
Geographical regions of risk in Southeast Asia for the case of Japanese encephalitis.
Fig. 1. Geographical regions of risk in Southeast Asia for the case of Japanese encephalitis. (Source: CDC).

While the majority of infected people show no or little symptoms, the individuals who do become symptomatic have to deal with a fatality rate of up to 30%. Notwithstanding the fact that there is no antiviral treatment once fallen ill, there are vaccinations available today which will fight off the infection in the event that you get sick in the future.

The JE virus (JEV) is transmitted to humans and horses primarily via mosquitos, most notably the Culex tritaeniorhynchus, though both humans and horses cannot spread it further. On their part, the mosquitoes have acquired the virus by feeding mainly on pigs. However, aside from swine, additional hosts have been identified, such as water birds, chickens, bats, pigeons, reptiles, amphibians, and ducks.

Detailed life cycle of the Japanese encephalitis virus.
Detailed life cycle of the Japanese encephalitis virus.
Fig. 2. Detailed life cycle of the Japanese encephalitis virus. (Source: UC Riverside).

By and large, JEV thrives during rainy and warm seasons in temperate regions, yet all year round in the (sub)tropics. Furthermore, the disease is overall regarded as rural, as the Culex tritaeniorhynchus typically breeds in areas of rice cultivation.

This helps us to understand how, for instance, the black-crowned night heron (a water bird) contributes to disseminating the virus, since it can engage in migratory behaviour to warmer regions during the winter and often resides in rice paddies.

The impact of seasonal migratory behaviour of birds (herons) on the transmission of the Japanese encephalitis virus.
The impact of seasonal migratory behaviour of birds (herons) on the transmission of the Japanese encephalitis virus.
Fig. 3. The impact of seasonal migratory behaviour of birds (herons) on the transmission of the Japanese encephalitis virus. (Source: HealthJade).

How both human and animal health are sensitive to changes in the climate and ecosystem is evident from a couple of observations.

First, Hui Zhang et al. point out that weather and climate changes have influenced the fact that JEV has now been signalled at higher altitudes in Tibet, China. Along similar veins but focusing on Nepal, Meghnath Dhimal et al. assert that climate change can augment the risk of a JE epidemic, given that rising temperatures are related to a higher incidence of JE.

Apart from altitude, James Pearce et al. state that the scope of transmission is even extending into more northerly latitudes. As a case in point, Ioanna Lytra and Nikolaos Emmanouel found a high population of the Culex tritaeniorhynchus in a rice field in Western Greece.

Not just that, the findings of Philip Mellor and Colin Leake suggest that, more generally, a boost in temperature might transform less efficient JEV-carriers into key disease transmitters, thereby plausibly expanding JEV’s geographical reach.

Second, Mukhtor Turaev shows how the black-crowned night heron — a JEV host — is able to migrate beyond its original range while at the same time not shying away from human-formed environments, if put under sufficient ecological pressure.

Third, as a result of increased meat production in Asia — in particular pork, chicken, and duck — and, subsequently, of a shift from rural agriculture to large-scale livestock farming in peri-urban zones, putting a greater number of potential JEV hosts closer to humans amplifies the chances of infection.

And conversely, precisely because of the trend of urbanization, more people move their homes to peri-urban neighbourhoods and therefore partake more frequently in urban animal husbandry as a way to survive.

In addition, even though JE is normally associated with pastoral regions, it is clear that, building on all of the above observations, both JEV transmission risks and JE incidence can no longer be neglected in (peri-)urban surroundings.

Indeed, JEV has been detected in pigs in Can Tho city, Vietnam, in a nine-year-old girl in Delhi, India, in two patients in Bangkok Province, Thailand, in pigs in the outskirts of Phnom Penh, Cambodia, in seven patients across Seoul, Incheon, and Daegu, South Korea, and, most recently, in two individuals in the suburbs of Seberang Perai, Malaysia.

Now that we have seen to which extent the three components of One Health interdepend, how does a One Health approach in the case of JE exactly look like in practice?

One example takes us to Papua New Guinea (PNG). A multi-partner project sponsored by the Australian government was set up between February 2019 and June 2020 to enhance surveillance strategies and response systems, so that JE could be more effectively and rapidly identified and contained. The One Health outlook within the project consisted of facilitating partnerships and coordination between local public health and veterinary organisations in PNG.

Next stop: Bangladesh. Although humans are usually vaccinated to prevent JE, Grand Challenges Canada supported a One Health project between March 2014 and September 2015 whereby pigs in north-western Bangladesh received vaccines to thwart human-animal JEV transmission. In this specific case, it was practical and cost-effective to treat pigs instead of humans, considering a relatively small pig population in the region.

The Animal-Environment-Human interface of the One Health approach.
The Animal-Environment-Human interface of the One Health approach.
Fig. 4. The Animal-Environment-Human interface of the One Health approach. (Source: University of Oslo).

Final destination: Cambodia, Laos, Vietnam, and Myanmar. Backed by Institut Pasteur (IP), this project has the two-fold objective of establishing an extensive body of knowledge around pathogens responsible for JE, among others, as well as strengthening hospital capacities to improve diagnosis and patient care. The project embraces a One Health perspective to their field work by amalgamating environmental, epidemiological, and sociological analysis with surveillance, control, and outbreak investigation methodologies.

Moreover, according to the IP project researchers, acknowledging the link between our interconnected nature and the threat of disease transmission provides fertile ground for getting a more substantial grip on the epidemiology of JE.

How Much Do We Wish to See?

Regardless of the current spread of the SARS-CoV-2 virus, many people around the world have been advocating already for years for closer collaboration between animal and human health. Not only that, the changes in our climate and ecosystems in the recent decades — and especially how they affect human and animal well-being — are becoming too prominent to ignore.

For that reason, the more we start to realize that the natural environment, people, and animals is a tightly knitted trinity, the more it might begin to dawn on us that the idea of One Health deserves proper attention in its own right.

Science writer at A Circle Is Round (https://acircleisround.com) • Exploring what science has to tell us about our interconnected nature •

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