Abstract
Costa Rica is a candidate to eliminate malaria by 2020. The remaining malaria transmission hotspots are located within the Huétar Norte Region (HNR), where 90% of the country’s 147 malaria cases have occurred since 2016, following a 33-month period without transmission. Here, we examine changes in transmission with the implementation of a supervised seven-day chloroquine and primaquine treatment (7DCPT). We also evaluate the impact of a focal mass drug administration (MDA) in January 2019 at Boca Arenal, the town in HNR reporting the greatest local transmission. We found that the change to a seven-day treatment protocol, from the prior five-day program, was associated with a 98% reduction in malaria transmission. The MDA helped to reduce transmission, keeping the basic reproduction number, RT, significantly below 1, for at least four months. However, following new imported cases from Nicaragua, autochthonous transmission resumed. Our results highlight the importance of appropriate treatment delivery to reduce malaria transmission, and the challenge that highly mobile populations, if their malaria is not treated, pose to regional elimination efforts in Mesoamerica and México.
Highlights
Malaria has been a major infectious disease in Costa Rica’s history [1,2]
Malaria was always present in the Huétar Norte Region (HNR) from 1976 to 2009, the number of cases was very small compared to what was observed in the Huétar Caribe Region (HCR), the main transmission hotspot in Costa Rica (Figure 1A)
In the HNR, transmission dropped following the change from the five-day radical cure to the seven-day treatment (Figure 1E) in 2008 (Figure 3A), where the annual mean malaria cases (±SD) significantly (Welch s t = 4.5, d.f. = 32.381, p-value = 6.8 × 10−5) decreased from 415 ± 511 during 1976–2008 to 8 ± 22 during 2009–2019
Summary
Malaria has been a major infectious disease in Costa Rica’s history [1,2]. Costa Rica is among the 21 countries most likely to eliminate malaria by 2020 [3]. In 1957, Costa Rica created a malaria surveillance and control program (MSCP) following Pan American Health Organization (PAHO) recommendations, and based malaria surveillance on passive case detection by the blood slide examination of patients with malaria symptoms in endemic areas [5,6]. Since 2009, IRS has been only deployed focally following the detection of malaria cases [7] This protocol is still in place [2] to affect a “transmission blockage”, where additional cases are actively searched within 100 m of a diagnosed case, using blood slide examination as a diagnostic, larval peri-domiciliary habitats are treated with larvicides, and three consecutive daily rounds of insecticide thermal fogging using permethrin [1.03% by volume] are applied. Indoor residual spraying with alpha-cypermethrin [0.03 g active ingredient/m2] is performed and IRS treatment is repeated every two months over a six-month period [7]
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