Adaptation to a Multiplex Bead Assay and Seroprevalence to Rift Valley Fever N Protein: Nampula Province, Mozambique, 2013-2014.

Rift Valley fever virus (RVFV) is endemic in sub-Saharan Africa (SSA), with outbreaks reported in the Arabian Peninsula and throughout SSA. The natural reservoir for RVFV are ruminants, with livestock populations exceeding 50% exposure rates in some areas of SSA. Transmission to humans can occur through exposure to infected livestock products or multiple species of mosquito vectors. In 2013 and 2014, cross-sectional surveys occurred in two districts of Nacala-a-Velha and Mecubúri in northern Mozambique, and participants provided blood samples for later serological assays. IgG against the N protein of RVFV was detected through multiplex bead assay (MBA). Of the 2,278 persons enrolled between the two surveys and study sites, 181 (7.9%, 95% confidence interval (CI): 6.9%-9.1%) were found to be IgG seropositive with increasing seroprevalence with older age and significantly higher seroprevalence in Nacala-a-Velha (10.5%, 8.8%-12.5%) versus Mecubúri (5.7%, 4.5%-7.1%). Seroprevalence estimates were not significantly different between the 2013 and 2014 surveys. Significant spatial clustering of IgG positive persons were consistent among surveys and within the two districts, pointing toward the consistency of serology data for making population-level assumptions regarding RVFV seroprevalence. A subset of persons (n = 539) provided samples for both the 2013 and 2014 surveys, and a low percentage (0.81%) of these were found to seroconvert between these two surveys. Including the RVFV N protein in an MBA antigen panel could assist elucidate RVFV exposure in SSA. IMPORTANCE Due to sporadic transmission, human contact with Rift Valley Fever Virus (RVFV) is difficult to ascertain at a population level. Detection of antibodies against RVFV antigens assist in estimating exposure as antibodies remain in the host long after the virus has been cleared. In this study, we show that antibodies against RVFV N protein can be detected from dried blood spot (DBS) samples being assayed by multiplex bead assay. DBS from two districts in northern Mozambique were tested for IgG against the N protein, and 7.9% of all enrolled persons were seropositive. Older persons, males, and persons residing closer to the coast had higher RVFV N protein seroprevalence. Spatial clustering of IgG positive persons was noted in both districts. These results show low exposure rates to RVFV in these two northern districts in Mozambique, and the ability to perform serology for the RVFV N protein from dried blood samples.

Multiplex serology for impact evaluation of bed net distribution on burden of lymphatic filariasis and four species of human malaria in northern Mozambique.

BACKGROUND: Universal coverage with long-lasting insecticidal nets (LLINs) is a primary control strategy against Plasmodium falciparum malaria. However, its impact on the three other main species of human malaria and lymphatic filariasis (LF), which share the same vectors in many co-endemic areas, is not as well characterized. The recent development of multiplex antibody detection provides the opportunity for simultaneous evaluation of the impact of control measures on the burden of multiple diseases. METHODOLOGY/PRINCIPAL FINDINGS: Two cross-sectional household surveys at baseline and one year after a LLIN distribution campaign were implemented in Mecubúri and Nacala-a-Velha Districts in Nampula Province, Mozambique. Both districts were known to be endemic for LF; both received mass drug administration (MDA) with antifilarial drugs during the evaluation period. Access to and use of LLINs was recorded, and household members were tested with P. falciparum rapid diagnostic tests (RDTs). Dried blood spots were collected and analyzed for presence of antibodies to three P. falciparum antigens, P. vivax MSP-119, P. ovale MSP-119, P. malariae MSP-119, and three LF antigens. Seroconversion rates were calculated and the association between LLIN use and post-campaign seropositivity was estimated using multivariate regression. The campaign covered 68% (95% CI: 58-77) of the population in Nacala-a-Velha and 46% (37-56) in Mecubúri. There was no statistically significant change in P. falciparum RDT positivity between the two surveys. Population seropositivity at baseline ranged from 31-81% for the P. falciparum antigens, 3-4% for P. vivax MSP-119, 41-43% for P. ovale MSP-119, 46-56% for P. malariae MSP-119, and 37-76% for the LF antigens. The seroconversion rate to the LF Bm33 antigen decreased significantly in both districts. The seroconversion rate to P. malariae MSP-119 and the LF Wb123 and Bm14 antigens each decreased significantly in one of the two districts. Community LLIN use was associated with a decreased risk of P. falciparum RDT positivity, P. falciparum LSA-1 seropositivity, and P. malariae MSP-119 seropositivity, but not LF antigen seropositivity. CONCLUSIONS/SIGNIFICANCE: The study area noted significant declines in LF seropositivity, but these were not associated with LLIN use. The MDA could have masked any impact of the LLINs on population LF seropositivity. The LLIN campaign did not reach adequately high coverage to decrease P. falciparum RDT positivity, the most common measure of P. falciparum burden. However, the significant decreases in the seroconversion rate to the P. malariae antigen, coupled with an association between community LLIN use and individual-level decreases in seropositivity to P. falciparum and P. malariae antigens show evidence of impact of the LLIN campaign and highlight the utility of using multiantigenic serological approaches for measuring intervention impact.

Avaliação da posse, acesso, uso de redes mosquiteiras e positividade da malária em dois distritos da Província de Nampula ­ 2013 e 2014 / Assessment of ownership, access, use of mosquito nets and positivity of malaria in two districts of the Province of Nampula ­ 2013 and 2014

Em 2013 o Ministério da Saúde distribuiu redes mosquiteiras impregnadas com insecticida de longa duração (REMTLD) em seis distritos da provincia de Nampula, incluindo Mecubúri e Nacala-a-Velha. Objectivos: Determinar a posse, acesso e uso das redes mosquiteiras e calcular as taxas de positividade dos testes rápidos (TDR) de malária, por agregados familiares (AFs) em 2014 comparando com 2013. Metodologia: Foi realizado um estudo transversal em duas fases: a linha de base em 2013 imediatamente após a campanha e outra um ano depois. Foram seleccionados aleatoriamente 16 agregados familiares (AFs) em 20 conglomerados, totalizando 320 AFs e 1280 membros de AFs por distrito por ano. Foi determinada a posse, acesso e uso das redes distribuídas no acesso universal e calculada a taxa de positividade dos testes rápidos (TDRs) de malária por AFs em 2014 e comparadas com os dados de 2013. Diferenças entre proporções foram calculados usando o Teste Chi-quadrado. Resultados: Em 2013 no dstrito de Nacala-a-Velha dos 1172 membros de agregados familiares (MAFs) 924 (78,8%) tinham acesso a REMTLD contra 51,9% (149/1443) em Mecubúri. Nas crianças abaixo de 5 anos de idade, Nacala-a-Velha, em 2013, teve uma positividade do TDRs de 47,3% contra 65,0% em 2014. Em Mecubúri a positividade em 2013 foi de 74,0% e em 2014 foi de 88,4%. Em 2014 e em Nacala-a-Velha 190/422 (45,0%) do MAFs com acesso a REMTLD foram positivos ao TDR contra 93/155 (60,0%) sem acesso a REMTLD (χ 2 =10,174; p =0,001). Em Mecubúri a positividade do TDR em membros de agregados familiares com acesso a REMTLD foi de 223/337 (66,2%) contra 272/364 (74,7%) sem acesso a REMTLD (χ 2 =6,169; p =0,013) Conclusão: O distrito de Nacala-a-Velha tem mais acesso a REMTLD do que Mecubúri. A positividade dos TDRs é maior em Mecubúri e nas pessoas sem acesso a rede. Recomendações: Educação para uso correcto das redes nas escolas e nos AFs após campanhas; melhorar as coberturas das campanhas

In 2013 the Mozambique Ministry of Health carried out a distribution campaign of long-lasting insecticide-treated bed nets (LLINs) in six districts, including Mecubúri and Nacala-a-Velha Districts, in Nampula Province. This study aimed to determine the coverage of the campaign and its impact on malaria prevalence. Methodology: A cross- sectional study in Nacala-a-Velha and Mecubúri Districts was conducted in two stages: at baseline in 2013 immediately following the campaign and one year later. Surveys were conducted in households randomly selected from 20 clusters in each district. The survey determined ownership of, access to, and use of LLINs. The rate of positivity by malaria rapid diagnostic test (RDT) in household members was compared between 2013 and 2014 and between those with and without access to LLINs. Results: In 2013 in the district of Nacala-a-Velha 924 out of 1172 (78,8%) household members had access to LLINs. Amongst household members in Mecubúri in 2013, LLIN access was 51,9% (749/1443). In children under 5 years of age, Nacala-a-Velha registered a rate of RDT positivity of 47,3% in 2013 vs 65,0% in 2014. For Mecubúri the positivity in 2013 was 74,0% compared to 88,4% in 2014. In 2014 in Nacala-a-Velha, 190/422 (45,0%) of household members with access to an LLIN were RDT-positive, compared to 93/155 (60,0%) of those without access to an LLIN (χ 2 =10,174; p =0,001). In Mecubúri, RDT positivity in those with LLIN access was 223/337 (66,2%), compared to 272/364 (74,7%) in those without access (χ 2 =6,169; p =0,013). Conclusion: LLIN access in Nacala-a-Velha was greater than in Mecubúri. The rate of RDT positivity was greater in Mecubúri and in people without access to LLINs. We recommend education and communication activities in schools and households to encourage LLIN use following distribution campaigns.