Cross-Sectional Study of Asymptomatic Malaria and Seroepidemiological Surveillance of Seven Districts in Gia Lai Province, Vietnam

Background: Malaria elimination by 2030 is an aim of many countries in the Greater Mekong Sub-region, including Vietnam. However, to achieve this goal and accelerate towards malaria elimination, countries need to determine the extent and prevalence of asymptomatic malaria as a potential reservoir for malaria transmission and the intensity of malaria transmission. The purpose of this study was to determine the prevalence of asymptomatic malaria and seropositivity rate in several districts of Gia Lai province in the Central Highlands of Vietnam.

Methods: A cross-sectional survey of asymptomatic malaria and serological testing was conducted in 3,283 people living at 14 communes across seven districts in Gia Lai province from December 2016 to January 2017. Finger prick capillary blood samples were tested for malaria using rapid diagnostic testing and polymerase chain reaction (PCR), as well as detecting antibodies against 3 Plasmodium falciparum and 4 P. vivax antigens by indirect enzyme-linked immunosorbent assay (ELISA). Age-seroprevalence curves were fitted using reverse catalytic models with maximum likelihood.

Results: The study population was predominantly male (65.9%, 2165/3,283), adults (88.7%, 2911/3,283), and of a minority ethnicity (72.2%, 2,371/3,283), with most participants being farmers and outdoor government workers (90.2%, 2,960/3,283). Using a small volume of blood (≈10 μL) the PCR assay revealed that 1.74% (57/3,283) of the participants had asymptomatic malaria ( P. falciparum 1.07%, P. vivax 0.40%, P. malariae 0.15% and mixed infections 0.12%). In contrast, the annual malaria prevalence rates for clinical malaria in the communities where the participants lived were 0.12% (108/90,395) in 2016 and 0.22% (201/93,184) in 2017. Seropositivity for at least one P. falciparum or one P. vivax antigen was 38.5% (1257/3262) and 31.1% (1,022/3,282), respectively. Age-dependent trends in the proportion of seropositive individuals in five of the districts discriminated the three districts with sustained low malaria prevalence from the two districts with higher transmission.

Conclusions: Asymptomatic Plasmodium carriers were found to be substantially more prevalent than clinical cases in seven districts of Gia Lai province, and a third of the population had serological evidence of previous malaria exposure. The findings add knowledge on the extent of asymptomatic malaria and transmission for developing malaria elimination strategies for Vietnam.

About Vysnova and SABER II

Vysnova Partners, Inc. is a leading provider of program management, public health research, acquisition support, and healthcare staffing to Federal clients. Vysnova prides itself in delivering services that improve global understanding of infectious diseases and enhance the quality and delivery of health services through innovation. With a diverse team of project managers, subject matter experts, and technical staff, Vysnova uses evidence-based, yet practical, solutions for better and stronger outcomes.

Vysnova Partners, a global health project management firm, was awarded the Southeast Asia Biosurveillance and Epidemiology Research (SABER) II program in 2018 to provide support for the Naval Medical Research Unit 2 (NAMRU-2) based in Singapore. Vysnova provides support for NAMRU-2 to evaluate novel diagnostics products and therapeutic interventions, test disease control strategies, and develop local expertise to detect and respond to emergent disease threats.  As the holder of the contract, Vysnova will support the ongoing development, performance, and management of research across the Southeast Asia region in collaboration with host-country partners.

The SABER II contract ensures the continuation of our efforts to understand and combat malaria, Zika, MERS-CoV, and other vector-borne illnesses. In addition to working with NAMRU-2 to develop preventative measures against infectious diseases and improve disease surveillance efforts, Vysnova is also working with NAMRU-2 under the Operational Research Support Across Southeast Asia to specifically target malaria infection. Some of Vysnova’s other work in this field includes helping to conduct malaria indicator surveys as a subcontractor to ICF under the seventh phase of the Demographic and Health Survey (DHS) Program for the U.S. Agency for International Development (USAID). Furthermore, Vysnova works with the Department of Health and Human Services at the Center for Disease Control and Prevention (CDC) to work with in-country partners in South America to perform testing and enhance surveillance in order to better understand and fight Zika infection in pregnant women and their children.

Article Type: Research

Funding Information: US Defense Health Program-Research, Development, Testing and Evaluation

Source: Malaria Journal