Unwitting Travelers May Act as Global Malaria Carriers

August 26, 2004
By Corinne Purtill

Travelers could be partly responsible for the spread of drug-resistant malaria across the globe a prospect doctors in Cambodia said was possible but probably a rare occurrence. 

In a paper published in the Friday issue of the journal Science, a group of researchers from the US, UK, South Africa and Thailand reported finding malaria parasites in Africa that had genetic mutations previously found almost exclusively in Southeast Asia. The mutation makes the parasite resistant to fansidar, an inexpensive malaria drug used in sub-Saharan Africa. 

The mutation, Cally Roper and colleagues suggest, was transferred from Southeast Asia to Africa by malaria-infected travelers, who may have unwittingly delivered a crippling blow to Africa's fight against malaria. 

"The resistance [genes] carried by these migrants are now spreading across Africa at an alarming rate, signaling the end of affordable malaria treatment and presenting sub-Saharan Africa with a public health crisis," the authors wrote. 

Cross-continent contamination is possible, said National Malaria Center adviser Dr Seshu Babu on Wednesday. A person bitten in Cambodia by a mosquito carrying the fansidar-resistant parasite, for example, could carry the parasite in his body for 10 days before showing symptoms. If he traveled to another country 
during that time and was bitten by a mosquito there, that mosquito would fly away with the drug-resistant parasite in its system, ready to infect the 
next victim. 

But "the frequency with which this occurs is not so high, not so alarming," Babu said.

Since travelers tend to stay away from the country's most malaria-prone areas, the chances of one becoming infected let alone an international carrier of the disease is low, doctors said. 

"It's not tourists who usually get malaria," said Dr Gavin Scott of the Tropical and Travelers Medical Clinic in Phnom Penh. Prevalent in border areas and 
forests, malaria has mostly been eradicated in tourist stops like Phnom Penh, Siem Reap and Sihanoukville.

According to the Science article, 30,000 malaria cases are brought to developed countries every year through travelers and migrants. The number of cases introducing foreign strains of the disease into countries with a pre-existing malaria problem are unknown, the researchers said.

Two-thirds of malaria parasites in Cambodia, Thailand and Burma are resistant to mefloquine and quinine, two anti-malaria drugs used often in other parts of the world, and "it is only a matter of time before these invade and establish in Africa," the authors wrote. 

To guard against that threat, the article concluded that travelers should be carefully screened before crossing borders an idea health officials in Cambodia dismissed as unrealistic in the face of the country's financial constraints. 

"Like screening for anything, it's costly. Who pays for screening?" Scott said.