Modelling recurrent clinical malaria episodes by Plasmodium vivax infection among children in Ethiopia
Background: Plasmodium vivax malaria is the second most prevalent malaria parasite in the world. It is characterized by recurrent episodes (relapses) produced by latent parasites (hypnozoites) in the liver. This study was intended to identify the associated factors with the first and recurrent confirmed P. vivax clinical episodes.
Methods: A two-year longitudinal cohort study that included weekly active case detection (ACD) of clinical malaria episodes in 2040 children aged <10 years was conducted in 16 villages near the Gilgel-Gibe hydroelectric power dam, between July 2008 and June 2010. A piecewise weibull proportional hazards (PWPH) model was used to identify the associated factors with the first P. vivax episode, whereas a subject frailty term was added to the model for identifying associated factors with recurrent P. vivax clinical episodes. The timing of recurrent episodes was modelled with the calendar and gap timescale.
Results: Overall, 307 (18.4%) children had at least one confirmed P. vivax clinical episode, and 1361 children were not presented any Plasmodium clinical episode during the entire follow up period. Most of children (259, 74.3%) with P. vivax episodes had only one episode, 35 (11.4%) had two recurrent episodes, 10 (3.2%) had three episodes and 3 (0.97%) had four episodes. The home distance to the Gilgel-Gibe dam showed no association with the first and the recurrent P.vivax malaria episodes. Age and season are significant factors in both first and recurrent clinical P.vivax episodes, older children showing a smaller malaria risk. The P.vivax clinical episode recurrence was higher in the long rainy than in the dry season with a hazard ratio (HR) of 2.99 (95% CI = 2.24, 3.99).
Conclusion: The seasonality of P.vivax malaria risk was significantly pronounced, rather than the effect of the Gilgel-Gibe dam on the malaria transmission. The information obtained using the recurrent P. vivax episode data did not result in additional insights to what is seen with the time-to-first episode data. Sustainable prevention and control programs, focusing on the rainfall pattern (season) of Ethiopia and the children's age, should be designed and implemented aiming to reduce the P.vivax malaria incidence.
D. S. Shebeshi,