Overview of Plasmodium vivax drug resistance:
Whilst our understanding of drug resistant Plasmodium falciparum, the most deadly form of the malaria parasite is quite well understood, the extent and nature of resistance in Plasmodium vivax parasites is for the most part is unknown, a major cause of illness and death especially in Latin America.
Plasmodium vivax infects 19-50 million people with malaria each year. Most of these cases occur in the Asia Pacific region where more than 2.2 billion people are at risk of infection.
Although drug resistance has forced most malaria endemic countries to abandon chloroquine treatment for P. falciparum malaria, chloroquine remains the frontline antimalarial treatment for P. vivax. However, this treatment is under threat from the emergence and spread of chloroquine resistant (CQR) P. vivax strains.
The challenge of eliminating Plasmodium vivax:
National malaria control programmes in the past have focussed their attention falciparum malaria, the more pathogenic form of the malaria parasite. As cases of falciparum malaria have decreased dramatically over the past two decades, the number of vivax malaria cases has actually increased.
There are many reasons for this P. vivax can be difficult to detect since it usually circulates at low levels in the blood. It can be present and infectious to the mosquito vectors, even when the person shows no symptoms. P. vivax can also to lie dormant in a person’s liver, reawakening weeks to months after the first infection to cause relapses of symptomatic malaria.
Chloroquine resistant forms of P. vivax parasite is now present in many countries. As the treatment becomes no longer effective in these regions, treatment failure and relapses is on the rise [1-3]. P. vivax has also developed drug resistance to sulfadoxine-pyrimethamine (SP) and potentially other antimalarial drugs such as mefloquine. See the WWARN Primaquine Literature Review for more information.
How to tackle Plasmodium vivax drug resistance:
Researchers are making significant progress in developing clinical trials protocols and drug susceptibility testing. They are also trying to uncover the mechanisms behind chloroquine resistant P. vivax. Understanding these processes will greatly improve global monitoring of chloroquine resistance.
For a comprehensive review of drug resistant P. vivax see the Chloroquine Resistant Plasmodium vivax Review.
Anstey NM, Douglas NM, Poespoprodjo JR, Price RN (2012) Plasmodium vivax: clinical spectrum, risk factors and pathogenesis. Adv Parasitol 80: 151-201.
Price RN, Douglas NM, Anstey NM (2009) New developments in Plasmodium vivax malaria: severe disease and the rise of chloroquine resistance. Curr Opin Infect Dis 22: 430-435.
Price RN, Tjitra E, Guerra CA, Yeung S, White NJ, et al. (2007) Vivax malaria: neglected and not benign. Am J Trop Med Hyg 77: 79-87.