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Imported malaria cases linked to air travel, historical ties between nations
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Air networks, traveler demographics, historical ties between nations and malaria endemicity all contribute to complex patterns by which malaria is spread to nonendemic countries, according to results of a meta-analysis.
“Tackling malaria remains a high priority internationally, with elimination and eradication back on the global agenda. In the past century, more than 50 countries have succeeded in eliminating the disease,” Andrew J. Tatem, PhD, of the department of geography and environment at the University of Southampton, United Kingdom, and colleagues wrote. “Nevertheless, although malaria is no longer endemic in these nations, increasing travel to endemic areas in recent decades means that the malaria-endemic world is becoming increasingly connected by population movements, and that imported malaria cases remain common.”
The researchers reviewed data on malaria cases in 40 nonendemic countries using national reports and searches of PubMed, Web of Science, Google Scholar and standard Google searches. Tatem and colleagues restricted their analysis to data obtained from 2005 to 2015, reviewing more than 50,000 malaria cases.
Researchers described the transfer of infections as “strongly skewed toward a small number of high-traffic routes.” France had more mean annual imported cases of malaria than any other country in the study (average 2,169 cases per year), Tatem and colleagues reported, followed by the U.K. (n = 1,898). The U.S. ranked third, with 1,511 cases, followed by Italy (n = 637) and Germany (n = 401). Ninety-two percent of cases originated in West Africa (56%), East Africa (13%), India (20%) and Papua New Guinea (3%). The strongest paths for malaria were between West Africa and France, as well as West Africa and the U.K., Tatem and colleagues wrote. France and the U.K. had a mean 2,492 cases per year imported from west Africa. However, the researchers pointed out that numerous other routes transferred more than 50 mean annual cases apiece. Those included cases transferred between the U.S. and India (average 149 per year), U.S. and West Africa (n = 716), and U.S. and Haiti (n = 52). Ninety-seven cases were transferred between Australia and Papua New Guinea, and 69 were transferred between the U.K. and Pakistan.
“As many countries move towards national malaria elimination, global eradication moves up the international agenda and the threat of spreading drug resistance grows, there is an increasing focus on malaria importation and the vulnerability of countries to resurgence,” Tatem and colleagues wrote. “Malaria parasites do not respect national borders, and with human mobility continuing to increase in its volumes and reach, increasing global connectivity, control and treatment strategies should account for the continued globalization of malaria.”
“Although the results are fairly intuitive and unsurprising, the relative novelty of this study comes from the fact that it used robust methods to overlay endemic malaria data with travel and migration patterns and species breakdowns to provide a contemporary overview of malaria importations,” Karin Leder, PhD, MPH, of the school of public health and preventive medicine, Monash University, Victoria, Australia, and Lin H. Chen, MD, of Harvard Medical School, wrote in an accompanying editorial.
“The method used could be applied to analyze other infectious disease importation and predict likelihood of disease acquisition.” – by Andy Polhamus
Disclosure: The researchers report no relevant financial disclosures.
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