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Increased Human Travel Has Resulted in Imported Malaria in Non-Endemic Countries

A new epidemiological study has mapped the incidence of imported malaria cases globally and provided context for the disease burden in places where the virus is not endemic.

The problems posed by malaria in countries where the virus remains endemic are obvious; however, the profound clinical challenges faced in regions where cases are “imported” are often overlooked.

That may change after the findings of a new epidemiological study published online by the journal The Lancet Infectious Diseases, which effectively maps the incidence of imported malaria cases globally, and provides some context for the disease burden in places where the virus is not endemic. The analysis was performed by an international team of researchers from Europe and Asia.

The authors noted, because clinicians in these countries aren’t typically “looking” for malaria, imported cases are often diagnosed at a later date, are more expensive to treat, and can sometimes result in secondary local transmission. Within malaria-endemic countries, the spread of the disease often increases antimalarial drug resistance, thus, jeopardizing the achievement of long-term eradication goals as established by the World Health Organization and others.

For their research, which was funded by the Bill and Melinda Gates foundation, the authors of The Lancet Infectious Disease paper analyzed a database of publicly available, nationally reported statistics on imported malaria over the past 10 years (from 2005 to 2015)—a period that encompassed more than 50,000 individual cases. They obtained data from 40 non-endemic countries and recorded all geographical variations.

They found that migration of the virus “strongly skewed towards a small number of high-traffic routes, with West Africa accounting for 56% of all imported cases to non-endemic countries with a reported travel destination, and France and the UK receiving the highest number of cases with more than 4,000 reported cases per year on average.” In general, they noted that most of this “movement” occurred between countries historically linked by emigration, language, and/or travel, such as French-speaking West African nations with France. There is strong spatial clustering of plasmodium species types in these areas.

The authors did not respond to requests for comment at press time. However, in their concluding remarks, they wrote, “The substantial growth in the reach and rates of human travel, in particular the air traffic network, in recent decades, has had a major effect on global disease epidemiology, including malaria. Rising rates of travel to and from endemic areas has resulted in imported malaria being frequently reported in malaria-free countries, with occasional secondary transmission… We noted clear and consistent patterns despite differences in data quality, completeness, and temporality, and data being indicative of the different surveillance systems and diagnostic capacities of the reporting countries. Our results underline the substantial geographical heterogeneities that exist in reported malaria case numbers and compositions in non-endemic countries.”

In addition, in a commentary published by the journal in conjunction with the paper, Karin Leder, MD, FRACP, PhD, MPH, DTMH, of the Lin H. Chen School of Public Health and Preventive Medicine at Monash University in Victoria, Australia, noted, “Compilation of various data sources, including the notifiable statistics analyzed by Tatem and colleagues, recognizes that travelers can serve as sentinels to provide information about disease activity in areas visited. Furthermore, travelers can be crucial in the spread of infectious diseases, posing a potential risk to areas that have the Anopheles vector but have eliminated endemic malaria. Additionally, assessment of aggregated data compiled from notification and surveillance activities offers up-to-date epidemiological information about disease activity, which can be used to refine appropriate pre-travel preventive advice and to prioritize diagnostic testing when assessing the ill returned traveler.”

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.