Researchers entering sampling data (photo credit: Zoonoses and Emerging Diseases).

In the cities of developing nations, where unregulated antibiotic use is common and livestock jostle with people amid often unsanitary conditions, scientists have found a potentially troubling vector for the dissemination of antimicrobial resistant bacteria: wildlife.

The epidemiological study published in the June 2019 issue of the journal Lancet Planetary Health shows that urban wildlife in Nairobi carry a high burden of clinically relevant antimicrobial resistant bacteria. The research team included scientists from the International Livestock Research Institute (ILRI), the University of Liverpool and the Kenya Medical Research Institute, among other research institutions.

Antimicrobial resistance is an increasingly serious threat to public health. Through misuse and overuse of antibacterial medication, more and more of the bacterial diseases that were once easily treated with antibiotics have become drug-resistant; these new strains of old germs require expensive and prolonged treatment at best and at worst can be lethal.

The study deployed teams of veterinary, medical, environmental and wildlife personnel to sample 99 households randomly chosen from Nairobi’s socio-economically diverse neighbourhoods.

The study found higher diversity of antimicrobial resistance in livestock and the environment than humans and wildlife. Rodents and birds were significantly more likely to carry resistance to multiple drugs when exposed to human and livestock waste through poor management practices, a common feature of lower-income neighbourhoods.

“This paper shows that contamination of urban environments with antimicrobial resistance is a serious issue. This is not just specific to Nairobi but findings can be extrapolated to other cities in Africa,” said Eric Fèvre, a joint appointed scientist at ILRI and professor of veterinary infectious diseases at the University of Liverpool.

“We tend to think of antimicrobial resistance in primarily medical terms, of developing new drugs and better using old ones. But we need to take an ecological approach to addressing this threat. Urban cities can address this by better urban planning, better waste disposal, better livestock husbandry practices. This can go far toward disrupting antimicrobial resistance exchange between wildlife, livestock and humans,” said Fèvre.

The lead author of the study, James Hassell, said, “Although we found no evidence to suggest that antimicrobial resistance carried by urban wildlife poses a direct threat to human health, that these animals harbour high levels of resistance to drugs used in human and animal medicine is particularly worrisome. Since wildlife are not treated with antibiotics, this is indicative of how pervasive antimicrobial resistance is in urban environments. Species that move freely across cities and further afield could disseminate resistance acquired in urban areas more widely.”

“We cannot address the rise of antimicrobial resistance without focusing on the environmental, ecological and social settings in which humans exist,” said Hassell.

Citation

Hassell, J.M., Ward, M.J., Muloi, D., Bettridge, J.M., Robinson, T.P., Kariuki, S., Ogendo, A., Kiiru, J., Imboma, T., Kang’ethe, E.K., Öghren, E.M., Williams, N.J., Begon, M., Woolhouse, M.E.J. and Fèvre, E.M. 2019. Clinically relevant antimicrobial resistance at the wildlife–livestock–human interface in Nairobi: An epidemiological study. Lancet Planetary Health 3(6): e259–e269.

Smallholder pig production in northern Viet Nam

Farmer Ma Thi Puong feeds her pigs on her farm near the northern town of Meo Vac, Vietnam. Intensification of livestock farming has been found to increase the risk of zoonotic disease transmission (photo credit: ILRI/Stevie Mann).

Modern farming practices, such as intensified livestock production, as well as environmental and biodiversity changes can be linked to the new wave of zoonotic diseases, according to a new study published in the 21 May 2013 edition of the Proceedings of the National Academy of Sciences (PNAS).

Human population growth and the expansion of agriculture to meet the ever-rising demand for food have been identified as the key drivers of recent outbreaks of emerging and re-emerging zoonotic diseases.

These human behavioural changes have led to encroachment of wildlife habitats, resulting in greater interactions between people, livestock and wildlife and increased chances of spillover of potential pathogens from wildlife to livestock and, consequently, people.

“Intensive livestock farming, especially of pigs and poultry, increases the risk of disease transmission due to increased population size and density,” the study reveals.

Environmental changes arising from settlement and agriculture, including land fragmentation, deforestation and replacement of natural vegetation with crops, alter the structure of wildlife population, giving rise to new environmental conditions that favour specific hosts, vectors and pathogens.

The study was carried out in form of a systematic review by a multidisciplinary team of researchers from the International Livestock Research Institute (ILRI) and the Royal Veterinary College, University of London.

The research team sought to analyze qualitatively scientific evidence on the effect of agricultural intensification and environmental change on the risk of zoonoses transmission at the interface of humans, livestock and wildlife.

While the study has identified a clear link between the threat of zoonotic disease and the wildlife-livestock interface, it does not adequately address the complex interactions between the environmental, social and biological drivers of pathogen emergence.

For this reason, there is need to carry out local interdisciplinary studies that can come up with locally relevant solutions to tackle the threat of emerging and re-emerging zoonoses, the authors conclude.

Delia Grace, veterinary epidemiologist and food safety expert at ILRI, is among the co-authors of the study. Grace also leads the agriculture-associated diseases theme of the CGIAR Research Program on Agriculture for Nutrition and Health.

Read the full-text article

Citation: Jones BA, Grace D, Kock R, Alonso S, Rushton J, Said MY, McKeever D, Mutua F, Young J, McDermott J and Pfeiffer DU. 2013. Zoonosis emergence linked to agricultural intensification and environmental change. Proceedings of the National Academy of Sciences of the United States of America (PNAS) 110(21): 8399-8404.