Monitoring the Emergence of Infectious Diseases

Zoonotic diseases that pass from animal to human are an international public health problem regardless of location — being infected with Campylobacter from eating undercooked chicken in the U.K. is not uncommon, for example — but in lower-income countries the opportunities for such pathogens to enter the food chain are amplified.

Professor Stephen Baker from Oxford University’s Center for Tropical Medicine and Global Health, Nuffield Department of Medicine, says that where he currently works in Vietnam, and across the region, humans have a very different way of interacting with animals being bred for food than would be familiar to those in the United Kingdom. If one were to travel to the Mekong Delta region (in the south of Vietnam) it would not be uncommon to see people who keep a large variety of farm animals in, or in close proximity to, their houses. It comes as little surprise that in a country where raw pig blood and pig uterus are commonly consumed, the number one cause of bacterial meningitis is Streptococcus suis, a colonizing bacterium of pigs.

The major problem of researching emerging infections is predicting how they arise and how we respond to them once they do.

Given the complexity of zoonotic disease emergence and transmission, it is very rare that an outbreak can be traced back to the first identified human or animal case — known as the “index case” — and this remains a substantial challenge. A lack of effective health and surveillance infrastructures in many lower income countries compounds this issue, as we are wholly reliant on individuals entering the healthcare system and getting diagnosed, which seldom happens.

The ideal scenario is that we can identify new pathogens with zoonotic potential in animals prior to them spilling over into humans. However, if we cannot achieve this we need to be aware of their existence and be able to respond by treating people effectively once they are infected. This means rapidly identifying patients with a particular infection, assessing the severity of their condition and diagnosing the agent. Therefore, having sentinel hospitals with well-trained clinical staff, good diagnostics and microbiology facilities is the best opportunity we are going to have to detect diseases.

The most recent example of this is a case of Trypanosoma evansi infection – a protozoan disease of animals and, rarely, humans – that we identified in a woman attending our hospital with an atypical disease presentation. Ultimately, we were able to trace this infection back to her cutting herself when butchering a buffalo in her family house during New Year celebrations – this was the first reported human case of T. evansi in Southeast Asia. Our ability to interact with animal health authorities permitted access to sampling bovines in the proximity of the patient’s house. We found a very high prevalence of the parasite in the blood of cattle and buffalo close to where the woman lived, highlighting a new zoonotic infection in the region and likely a sustained risk.

Diagnostic information has also been vital in data we published detailing an outbreak of fluoroquinolone-resistant Shigella sonnei. The reason we found this organism was that one of my clinical colleagues was culturing organisms from children with severe diarrheal disease, and realized that these samples had come from children who had been admitted to hospital with a more persistent form of the infection, and several appeared to relapse with the same syndrome. When we investigated the antimicrobial susceptibility profile of the isolated Shigella, we observed that the bacteria were highly resistant to fluoroquinolones – the antimicrobials that are used routinely to treat this infection in Vietnam (and indeed globally). We then conducted more clinical and laboratory investigations and found more cases in Vietnam and further afield. Through genome sequencing and a group of international collaborators, we could accurately piece together the emergence of this novel strain into Vietnam, other parts of Asia, Europe and Australia.

These finding were largely serendipitous, but if you are not looking then you cannot find. Unfortunately, this approach is not a long-term strategy for monitoring and preventing the emergence of such pathogens. Sadly, the infrastructure improvements and long-term health studies that are needed to achieve a more sustainable model in lower income countries are an expensive undertaking, but without them healthcare improvements and changes to infectious disease policy will be difficult to achieve.

Bakers says that Vietnam has changed beyond recognition since his arrival in 2007. Huge economic investment and political stability has had positive effects on healthcare in the country, and across the region. However, many challenges remain; a growing population, increasing demands for animal protein, and the looming cloud of antimicrobial resistance in everyday pathogens suggest that Southeast Asia will continue to be a key region in driving global health security.

— Read more in Stephen Baker, “Emerging infectious diseases in Asia,” Microbiology Today (February 2017)

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