Zoonotic pathogens: When disease outbreaks follow unusual patterns

The World Health Organisation (WHO) recently sounded the alarm concerning a growing risk of disease outbreaks in Africa attributable to zoonotic pathogens, after finding a 63 per cent rise in the number of zoonotic outbreaks in the last decade.

Zoonotic diseases (or zoonoses), according to the Centres for Disease Control and Prevention (CDC), are caused by harmful viruses, bacteria, parasites, or fungi that are carried by animals but can sometimes spread to humans.

On July 18, just days after WHO's press conference, Tanzania's Minister for Health, Ummy Mwalimu, confirmed the culprit of more than 20 cases of a mysterious illness resulting in three deaths in Tanzania, to be leptospirosis- a bacterial disease spread mostly by coming into contact with the urine of an infected animal; or water, soil, or food.

A day earlier, Ghana reported its first cases of the Marburg virus after two deaths, with 98 others placed in isolation as suspected contact cases.

The SARS-CoV-2 virus that causes Covid-19 is also zoonotic.

With increased movement of people, exchange of goods and foods within and across borders coupled with environmental degradation has seen diseases previously confined to a limited population spreading widely as people and animals seek favourable surroundings.

The One Health approach that has been defined by an advisory panel of the Food and Agriculture Organisation (FAO), Uneo, the World Organisation for Animal Health (WOAH) and WHO as "an integrated, unifying approach that aims to sustainably balance and optimise the health of people, animals and ecosystems" requires an appreciation of the interconnectedness of human, animal, plant, and other occupants of the biosphere as integral to our collective well-being.

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The One Health approach aims to draw from the expertise of communities and multiple disciplines to tackle zoonotic diseases and other health threats.

In February 2022, Kenya launched its One Health Strategic Plan for the Prevention and Control of Zoonotic Diseases (2021-2025) while the African Union also established an Inter-agency Group on One Health in June this year and tasked with the development of strategy, co-ordination, implementation, monitoring and evaluation of One Health for zoonotic diseases.

The risks presented by 'reverse zoonosis' must also be taken seriously. According to WOAH, reverse zoonosis occurs when a pathogen passes from a human to an animal; most recently exemplified by domestic and wild animals that included dogs, pet hamsters, and deer being infected with SARS-CoV-2 by humans. WOAH notes that thus far, 23 animal species in 36 countries globally have been infected with SARS-CoV-2.

A major concern with reverse zoonosis as stated by WOAH, is the potential for the "further evolution of the virus in animals, and a future reintroduction of the virus into humans at a later date."

We cannot tell what form these evolved viruses might take; or their effects on the human and animal populations, making for a cauldron of uncertainty in terms of mitigation and planning.

Finally, a word of caution: Despite the WHO's legitimate concerns about zoonoses in Africa, there must be as much focus on investigating and determining the causes of outbreaks in other regions of the globe, in view of an emerging trend of zoonotic outbreaks in regions where they have not been historically reported.

As at 21 July, the CDC reported 15,848 cases of monkey pox, of which 15,605 have occurred in countries where monkey pox has not historically been reported. Of the 72 countries reporting cases of monkey pox, only six have historically reported similar cases before.

The question concerning the causes of unusual outbreaks must be approached with an open mind; without a predetermined mindset or bias as to their origins.

In a situation where disease outbreaks seem to following uncommon patterns, care must be taken not to unjustifiably single out a particular region in terms of focus, or in the language used when reporting outbreaks; bearing in mind unintended consequences such as the stereotyping and stigmatising of persons from those regions.

Dr Esther Muiruri is a Bioethicist, lawyer and a visiting course facilitator at Aga Khan University Medical College, EA