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Plasmodium vivax malaria accounts for 60-65% of total malaria cases in India. Vivax infections cause significant morbidity since in addition to the primary infection, dormant liver stages (hypnozoites) may re-emerge long after completion of full course of chloroquine treatment (25mg/kg) to cause relapses. The relapse patterns of P vivax are broadly divided into the tropical or Chesson strain type characterized by an early primary attack followed by a short latent period, the appearance of frequent relapses and the St. Elizabeth strain of the temperature type by an early primary attack and a long latent period of 6-14 months followed by relapses . Primaquine is the drug used for radical cure of vivax malaria.
The National Malaria Eradication Programme of India recommends primaquine in a dose of 15 mg/day for 5 days to all vivax malaria patients, which is also followed in the Armed Forces. WHO while advocating the treatment of malaria including prevention of relapses has categorized population based on their immune status with respect to malaria-immune, semi-immune and non-immune. While they advocate a 5 day primaquine regimen for the first two categories, they recommend a 14 day schedule for the non immune population. For some reasons, we in India have considered ourselves as either immune or semi-immune. Practically speaking, there can be no immune population. Further, immunity in malaria is so diverse on account of strain variation within the same species that a migratory or floating population like the Armed Forces can never be considered immune or semi-immune. It has an appropriate label as non-immune since we may be semi-immune to a strain at one place but moving on to another place may not be semi-immune or immune to the strain prevalent there. Most western authorities have also advocated a 14 day primaquine regimen . However. for logistic and financial reasons. 5 day primaquine regimen has been preferred in India.
Various relapse patterns have been reported from different parts of India. Adak et al reported in 1998. three relapse patterns from Northern India-tropical. temperate and intermediate . A recently concluded study from Mumbai has reported a relapse pattern of predominantly tropical type. in which most of the relapses occurred in first 6 months of completion of chloroquine therapy . A comparison of no primaquine. 5 day primaquine and 14 day primaquine has shown that the relapse rate is zero with 14 day regimen, 19.4% with the 5 day regimen and 11.4% with no primaquine regimen .
Another study has shown that rhe relapse rate with 5 day primaquine regimen is 13% , while it was 12.67% on no primaquine regimen as recently reported from Mumbai . All patients who relapsed in this study showed complete response to the 14 day primaquine regimen.
Another aspect that has often been deliberated is, whether the relapses that occur in vivax cases are true relapses or a fresh infection. Scientifically, only polymerase chain reaction test can determine this, which can be undertaken only in special circumstances or for research purpose and not as a routine. The protagon ists of ‘fresh vivax infection’ subscribe to the view on account of endemicity and transmission potential of malaria existing locally. This argument can well be countered in view of the above-mentioned studies wherein the rate of relapse (should we say suffering once again) was zero with 14 day primaquine regimen.
Given the 13-19.4% relapse rate with 5 day primaquine regimen. the tropical type of relapse and complete response to the 14 day primaquine regimen. the utility of the 5 day regimen needs to be considered again. We have also seen cases of vivax malaria that have relapsed after 5 day primaquine regimen (personal communication. data not available).
Based on the available data. we need to revise our existing national policy as well as that in the Armed Forces on radical cure of vivax malaria. Adopting the 14 day primaquine regimen will increase the duration of hospital admission from vivax malaria. but will ultimately decrease the expenditure incurred per patient of vivax malaria. We hope through this communication, to generate opinion from the experts in the field of malariology and also encourage debate on this issue at a larger forum.