First sero-prevalence of dengue fever specific immunoglobulin G antibodies in Western and North-Western provinces of Zambia: a population based cross sectional study.

BACKGROUND: Dengue fever is a tropical infectious disease caused by dengue virus (DENV), a single positive-stranded RNA Flavivirus. There is no published evidence of dengue in Zambia. The objective of the study was to determine the sero-prevalence and correlates for dengue fever specific IgG antibodies in Western and North-Western provinces in Zambia. METHODS: A randomized cluster design was used to sample participants for yellow fever risk assessment. In order to rule out cross reactivity with other flaviviruses including dengue, differential antibody tests were done by ELISA. Data was processed using Epi Data version 3.1 and transferred to SPSS version 16.0 for analysis. Bivariate and multivariate analyses were performed to determine the association of dengue fever with various factors. Unadjusted odds ratios (OR), adjusted odds ratios (AOR) and their 95% confidence intervals (CI) are reported. RESULTS: A total of 3,624 persons were sampled for dengue virus infection of whom 53.3% were female and 23.9% were in the 5-14 years age group. Most persons in the survey attained at least primary education (47.6%). No significant association was observed between sex and dengue virus infection (p = 1.000). Overall, 4.1% of the participants tested positive for Dengue IgG. In multivariate analysis, the association of age with Dengue infection showed that those below 5 years of age were 63% (AOR = 0.37; 95% CI [0.16, 0.86]) less likely to be infected with Dengue virus compared to those aged 45 years or older. A significant association was observed between grass thatched roofing and Dengue infection (AOR = 2.28; 95% CI [1.15, 4.53]) Respondents who used Insecticide Treated Nets (ITN) were 21% (AOR = 1.21; 95% CI [1.01, 1.44]) more likely to be infected with dengue infection than those who did not use ITNs. Meanwhile, participants who visited Angola were 73% (AOR = 1.73; 95% CI [1.27, 2.35]) more likely to be infected with Dengue virus than those who did not visit Angola. CONCLUSION: This study provides the first evidence of dengue infection circulation in both North-Western and Western provinces of Zambia. It is important that surveillance activities for Dengue and diagnostic systems are expanded and strengthened, nationwide in order to capture information related to dengue virus and other flaviviruses.

Distribution of yellow fever vectors in Northwestern and Western Provinces, Zambia.

OBJECTIVE: To determine the distribution of yellow fever (YF) vectors species in Northwestern and Western of Zambia, which sampled mosquitoes inside and outside houses in rural, urban, peri-urban and forest areas. METHODS: Back-pack aspirators spray catches and CDC light traps collected adult mosquitoes including 405 Aedes, 518 Anopheles, 471 Culex and 71 Mansonia. Morphological vector identification and PCR viral determination were done at a WHO Regional Reference Centre (Institute Pasteur Dakar), Senegal. RESULTS: The two main YF vectors were Aedes (Stegomyia) aegypti (Ae. aegypti) and Aedes (Stegomyia) africanus. The first was collected in peri-urban areas and the later was in forest areas, both sparsely distributed in Northwestern Province, where the 0.43 Breteau and 1.92 container indexes, respectively implied low risk to YF. Aedes (Aedimorphus) mutilus; Aedes (Aedimorphus) minutus and Aedes (Finlaya) wellmani were also found in Northwestern, not in Western Province. No Aedes were collected from rural peri-domestic areas. Significantly more Aedes species (90.7%, n=398) than Anopheles (9.1%, n=40) were collected in forest areas (P<0.001) or Culex species (0.2%, n=2) (P<0.001). Ae. aegypti was found only in a discarded container but not in flower pots, old tyres, plant axils, discarded shallow wells, disused container bottles and canoes inspected. CONCLUSIONS: Ae. aegypti and Aedes africanus YF vectors were found in the study sites in the Northwestern Province of Zambia, where densities were low and distribution was sparse. The low Breteau index suggests low risk of YF in the Northwestern Province. The presence of Aedes in Northwestern Province and its absence in the Western Province could be due to differing ecological factors in the sampled areas. Universal coverage of vector control interventions could help to reduce YF vector population and the risk to arthropod-borne virus infections.