The impact of targeted malaria elimination with mass drug administrations on falciparum malaria in Southeast Asia: A cluster randomised trial.

BACKGROUND: The emergence and spread of multidrug-resistant Plasmodium falciparum in the Greater Mekong Subregion (GMS) threatens global malaria elimination efforts. Mass drug administration (MDA), the presumptive antimalarial treatment of an entire population to clear the subclinical parasite reservoir, is a strategy to accelerate malaria elimination. We report a cluster randomised trial to assess the effectiveness of dihydroartemisinin-piperaquine (DP) MDA in reducing falciparum malaria incidence and prevalence in 16 remote village populations in Myanmar, Vietnam, Cambodia, and the Lao People's Democratic Republic, where artemisinin resistance is prevalent. METHODS AND FINDINGS: After establishing vector control and community-based case management and following intensive community engagement, we used restricted randomisation within village pairs to select 8 villages to receive early DP MDA and 8 villages as controls for 12 months, after which the control villages received deferred DP MDA. The MDA comprised 3 monthly rounds of 3 daily doses of DP and, except in Cambodia, a single low dose of primaquine. We conducted exhaustive cross-sectional surveys of the entire population of each village at quarterly intervals using ultrasensitive quantitative PCR to detect Plasmodium infections. The study was conducted between May 2013 and July 2017. The investigators randomised 16 villages that had a total of 8,445 residents at the start of the study. Of these 8,445 residents, 4,135 (49%) residents living in 8 villages, plus an additional 288 newcomers to the villages, were randomised to receive early MDA; 3,790 out of the 4,423 (86%) participated in at least 1 MDA round, and 2,520 out of the 4,423 (57%) participated in all 3 rounds. The primary outcome, P. falciparum prevalence by month 3 (M3), fell by 92% (from 5.1% [171/3,340] to 0.4% [12/2,828]) in early MDA villages and by 29% (from 7.2% [246/3,405] to 5.1% [155/3,057]) in control villages. Over the following 9 months, the P. falciparum prevalence increased to 3.3% (96/2,881) in early MDA villages and to 6.1% (128/2,101) in control villages (adjusted incidence rate ratio 0.41 [95% CI 0.20 to 0.84]; p = 0.015). Individual protection was proportional to the number of completed MDA rounds. Of 221 participants with subclinical P. falciparum infections who participated in MDA and could be followed up, 207 (94%) cleared their infections, including 9 of 10 with artemisinin- and piperaquine-resistant infections. The DP MDAs were well tolerated; 6 severe adverse events were detected during the follow-up period, but none was attributable to the intervention. CONCLUSIONS: Added to community-based basic malaria control measures, 3 monthly rounds of DP MDA reduced the incidence and prevalence of falciparum malaria over a 1-year period in areas affected by artemisinin resistance. P. falciparum infections returned during the follow-up period as the remaining infections spread and malaria was reintroduced from surrounding areas. Limitations of this study include a relatively small sample of villages, heterogeneity between villages, and mobility of villagers that may have limited the impact of the intervention. These results suggest that, if used as part of a comprehensive, well-organised, and well-resourced elimination programme, DP MDA can be a useful additional tool to accelerate malaria elimination. TRIAL REGISTRATION: ClinicalTrials.gov NCT01872702.

History of malaria treatment as a predictor of subsequent subclinical parasitaemia: a cross-sectional survey and malaria case records from three villages in Pailin, western Cambodia.

BACKGROUND: Treatment of the sub-clinical reservoir of malaria, which may maintain transmission, could be an important component of elimination strategies. The reliable detection of asymptomatic infections with low levels of parasitaemia requires high-volume quantitative polymerase chain reaction (uPCR), which is impractical to conduct on a large scale. It is unknown to what extent sub-clinical parasitaemias originate from recent or older clinical episodes. This study explored the association between clinical history of malaria and subsequent sub-clinical parasitaemia. METHODS: In June 2013 a cross-sectional survey was conducted in three villages in Pailin, western Cambodia. Demographic and epidemiological data and blood samples were collected. Blood was tested for malaria by high-volume qPCR. Positive samples were analysed by nested PCR to determine the Plasmodium species. To identify previous episodes of malaria, case records were collected from village malaria workers and local health facilities and linked to study participants. RESULTS: Among 1343 participants, 40/122 (32.8 %) with a history of clinical malaria were parasitaemic during the cross-sectional survey, compared to 172/1221 (14.1 %) without this history (p < 0.001). Among the 212 parasitaemic participants in the survey, 40 (18.9 %) had a history of clinical malaria, compared to 87 out of 1131 (7.7 %) parasite-negative participants; p < 0.001, adjusted OR 3.3 (95 % CI; 2.1-5.1). A history of Plasmodium vivax was associated with sub-clinical P. vivax parasitaemia in the survey (p < 0.001), but this association was not seen with Plasmodium falciparum (p = 0.253); only three participants had both P. falciparum parasites in the survey and a clinical history of P. falciparum. CONCLUSIONS: A clinical episode of vivax malaria was associated with subsequent sub-clinical parasitaemia. Treatment of P. vivax with artemisinin-based combination therapy without primaquine often resulted in recurrent episodes. Targeting individuals with a history of clinical malaria will be insufficient to eliminate the sub-clinical reservoir as they constitute a minority of parasitaemias.

Persistent Plasmodium falciparum and Plasmodium vivax infections in a western Cambodian population: implications for prevention, treatment and elimination strategies.

BACKGROUND: Subclinical Plasmodium parasitaemia is an important reservoir for the transmission and persistence of malaria, particularly in low transmission areas. METHODS: Using ultrasensitive quantitative PCR (uPCR) for the detection of parasitaemia, the entire population of three Cambodian villages in Pailin province were followed for 1 year at three-monthly intervals. A cohort of adult participants found initially to have asymptomatic malaria parasitaemia was followed monthly over the same period. RESULTS: The initial cross sectional survey in June 2013 (M0) of 1447 asymptomatic residents found that 32 (2.2%) had Plasmodium falciparum, 48 (3.3%) had P. vivax, 4 (0.3%) had mixed infections and in 142/1447 (9.8%) malaria was detected but there was insufficient DNA to identify the species (Plasmodium. species). Polymorphisms in the 'K13-propeller' associated with reduced susceptibility to artemisinin derivatives (C580Y) were found in 17/32 (51%) P. falciparum strains. Monthly follow-up without treatment of 24 adult participants with asymptomatic mono or mixed P. falciparum infections found that 3/24 (13%) remained parasitaemic for 2-4 months, whereas the remaining 21/24 (87%) participants had cleared their parasitaemia after 1 month. In contrast, 12/34 (35%) adult participants with P. vivax mono-infection at M0 had malaria parasites (P. vivax or P. sp.) during four or more of the following 11 monthly surveys. CONCLUSIONS: This longitudinal survey in a low transmission setting shows limited duration of P. falciparum carriage, but prolonged carriage of P. vivax infections. Radical treatment of P. vivax infections by 8-aminoquinoline regimens may be required to eliminate all malaria from Cambodia. Trial registration ClinicalTrials.gov NCT01872702.

Smartphones for community health in rural Cambodia: A feasibility study.

Background: Village Malaria Workers (VMWs) are lay people trained to provide a valuable role in frontline testing and treatment of malaria in rural villages in Cambodia. Emergence of artemisinin-resistant malaria highlights the essential role of such VMWs in surveillance and early treatment of malaria. Smartphone technology offers huge potential to support VMWs in isolated and resource-poor settings.  Methods: We investigated the feasibility of issuing established VMWs with a smartphone, bespoke Android application and solar charger to support their role. 27 VMWs in Kampong Cham and Kratie provinces participated.  Results: 26/27 of the smartphones deployed were working well at study completion twelve months later. Interviews with VMWs using quantitative and qualitative methods revealed pride, ease of use and reports of faster communication with the smartphone. VMWs also expressed a strong wish to help people presenting with non-malarial fever, for which further potential supportive smartphone applications are increasingly available.  Conclusions: As a result of this pilot study, two smartphone based reporting systems for malaria have been developed at the Cambodian National Malaria Center, and the programme is now being extended nationwide. The full code for the smartphone application is made available to other researchers and healthcare providers with this article. Smartphones represent a feasible platform for developing the VMW role to include other health conditions, thus maintaining the relevance of these important community health workers.

A multi-level spatial analysis of clinical malaria and subclinical Plasmodium infections in Pailin Province, Cambodia.

BACKGROUND: The malaria burden is decreasing throughout the Greater Mekong Subregion, however transmission persists in some areas. Human movement, subclinical infections and complicated transmission patterns contribute to the persistence of malaria. This research describes the micro-geographical epidemiology of both clinical malaria and subclinical Plasmodium infections in three villages in Western Cambodia. METHODS: Three villages in Western Cambodia were selected for the study based on high reported Plasmodium falciparum incidence. A census was conducted at the beginning of the study, including demographic information and travel history. The total population was 1766. Cross-sectional surveys were conducted every three months from June 2013 to June 2014. Plasmodium infections were detected using an ultra-sensitive, high-volume, quantitative polymerase chain reaction (uPCR) technique. Clinical episodes were recorded by village health workers. The geographic coordinates (latitude and longitude) were collected for all houses and all participants were linked to their respective houses using a demographic surveillance system. Written informed consent was obtained from all participants. RESULTS: Most clinical episodes and subclinical infections occurred within a single study village. Clinical Plasmodium vivax episodes clustered spatially in each village but only lasted for a month. In one study village subclinical infections clustered in geographic proximity to clusters of clinical episodes. The largest risk factor for clinical P. falciparum episodes was living in a house where another clinical P. falciparum episode occurred (model adjusted odds ratio (AOR): 6.9; CI: 2.3-19. 8). Subclinical infections of both P. vivax and P. falciparum were associated with clinical episodes of the same species (AOR: 5.8; CI: 1.5-19.7 for P. falciparum and AOR: 14.6; CI: 8.6-25.2 for P. vivax) and self-reported overnight visits to forested areas (AOR = 3.8; CI: 1.8-7. 7 for P. falciparum and AOR = 2.9; CI: 1.7-4.8 for P. vivax). DISCUSSION: Spatial clustering within the villages was transient, making the prediction of spatial clusters difficult. Interventions that are dependent on predicting spatial clusters (such as reactive case detection) would only have detected a small proportion of cases unless the entire village was screened within a limited time frame and with a highly sensitive diagnostic test. Subclinical infections may be acquired outside of the village (particularly in forested areas) and may play an important role in transmission.

Association between Subclinical Malaria Infection and Inflammatory Host Response in a Pre-Elimination Setting.

BACKGROUND: Subclinical infections in endemic areas of Southeast Asia sustain malaria transmission. These asymptomatic infections might sustain immunity against clinical malaria and have been considered benign for the host, but if they are associated with chronic low-grade inflammation this could be harmful. We conducted a case-control study to explore the association between subclinical malaria and C-reactive protein (CRP), an established biomarker of inflammation. METHODS: Blood samples from asymptomatic villagers in Pailin, Western Cambodia were tested for malaria by high-volume ultra-sensitive polymerase chain reaction (uPCR) to determine the Plasmodium species. Plasma CRP concentration was measured in 328 individuals with parasitaemia (cases) and compared with: i) the same individual's value at the first time point when they had no detectable parasites (n = 282); and ii) age- sex- and village-matched controls (n = 328) free of Plasmodium infection. Plasma CRP concentrations were compared against thresholds of 3mg/L and 10mg/L. Subgroup analysis was carried out for cases with P vivax and P falciparum mono-infections. RESULTS: Median plasma CRP level for all samples was 0.59mg/L (interquartile range: 0.24-1.64mg/L). CRP concentrations were higher in parasitaemic individuals compared with same-person-controls (p = 0.050); and matched-controls (p = 0.025). 4.9% of samples had CRP concentrations above 10mg/L and 14.6% were above 3mg/L. Cases were more likely to have plasma CRP concentrations above these thresholds than age/sex matched controls, odds ratio 3.5 (95%CI 1.5-9.8) and 1.8 (95%CI 1.1-2.9), respectively. Amongst cases, parasite density and CRP were positively correlated (p<0.001), an association that remained significant when controlling for age and fever. Individuals with P.vivax mono-infections had the highest plasma CRP concentrations with the greatest association with parasitaemia. DISCUSSION: In this setting persistent malaria infections in asymptomatic individuals were associated with moderately elevated plasma CRP concentrations; chiefly evident in cases with P.vivax mono-infections. As well as interrupting malaria transmission within the community, treatment of asymptomatic malaria infections, in particular radical cure of vivax malaria, may benefit the health of infected individuals.

Predictors of immune response and reactogenicity to AS03B-adjuvanted split virion and non-adjuvanted whole virion H1N1 (2009) pandemic influenza vaccines.

In 2009, 943 children aged 6 months to 10 years were randomised to receive two doses of an oil-in water AS03B-adjuvanted split virion or a non-adjuvanted whole virion H1N1 (2009) vaccine. The large numbers allowed investigation of possible predictors of immune response and reactogenicity. We used regression analysis to examine the effect of variables including past receipt of seasonal vaccine, antipyretics post-vaccination, interval between doses and pre-existing antibodies to H1N1 (2009) on immunogenicity. We also examined the relationship between immunogenicity and reactogenicity and whether prior infection or underlying conditions affected reactogenicity. For both vaccines, haemagglutination-inhibition titres were 60% higher in children with fever ≥38 °C after vaccination and 29% lower in those previously given seasonal vaccine. Early use of antipyretics did not affect immunogenicity. Post-vaccination titres were higher with longer intervals between doses and in those with evidence of prior infection, but reactogenicity in the latter was unaffected. In the adjuvanted vaccine group, reactions were more common in children with atopy. Both vaccines were safe and immunogenic in those with prior infection. Reduction in the interval between doses for earlier protection would be at the cost of reduced immunogenicity. The effect of seasonal vaccine on immunogenicity merits further investigation.