Spatial and temporal patterns of dengue transmission along a Red Sea coastline: a longitudinal entomological and serological survey in Port Sudan city

Abstract

Background: Dengue is an emerging health problem in several coastlines along the Red Sea. The objective of the present work is to elucidate spatial and temporal patterns of dengue transmission in Port Sudan.

Methods/findings: A longitudinal study with three cross-sectional surveys was carried out in upper, middle and lower class neighborhoods, from November 2008 to October 2009. Monthly, entomological surveys were followed by serological surveys in dengue vector-positive houses. Meteorological records were obtained from two weather stations in the city during the same time. Overall, 2825 houses were inspected. Aedes aegypti represented 65% (35,714/54,944) and 68% (2526/3715) of the collected larvae and pupae, respectively. Out of 4640 drinking water containers, 2297 were positive for Ae. aegypti. Clay-pots "Zeirr" followed by plastic barrels were key productive containers for pupae of dengue vector, 63% (n = 3959) and 26% (n = 1651), respectively. A total of 791 blood samples were tested using PanBio Capture/Indirect IgM ELISA. Overall, the sero-prevalence rate of dengue ranged between 3%-8% (41/791), compared to an incidence of 29-40 new cases per 10,000 (193/54886) in the same examined population. Lower and middle class neighborhoods had higher entomological indices compared with upper class ones (p<0.001). Although, dengue incidence rate was significantly lower in the middle and lower class neighborhoods (F = 73.97, d.f. = 2, p<0.001), no difference in IgM prevalence was shown. The city is subject to two transmission peaks in the winter (i.e. November-January), and summer (i.e. June-August). The serological peaks of dengue are preceded by entomological peaks that occur before the onset of winter (November) and summer (March) respectively.

Conclusion: Dengue incidence is heterogeneously distributed across the neighborhoods of Port Sudan and exhibits a bi-cyclic intra-annual pattern. Hence, it should be feasible to carry out timely vector control measures to prevent or reduce dengue transmission.

Figure 1. Port Sudan map.

Sketch map of Port Sudan city shows approximate location of the study neighborhoods.

Figure 2. Types of productive containers of dengue vector.

Clay pots and barrels are among the nine productive containers of Aedes aegypti (L) identified in Port Sudan during the study period (November 2008–October 2009).

Figure 3. Monthly total numbers of pupae of Aedes aegypti, P/D and P/C indices in Port Sudan.

Two peaks of pupae indices of Dengue vector: pupae/person Index (P/P) and pupae per Children<5 yrs (P/C), are shown for November and April–May during the period (November 2008–October 2009).

Figure 4. Seasonality of Stegomyia indices in Port Sudan.

The highest Stegomyia indices of Dengue vector, HI, BI and CI was shown for March, April–May and July during the period (November 2008–October 2009).

Figure 5. Monthly larval ratio (late/early stages) of Ae. aegypti in Port Sudan city.

Numbers and ratios of early stages (1st/2nd) and late stages (3rd/4th) of the dengue vector collected.

Figure 6. Association of IgM seroprevalence and entomological indices.

Monthly patterns of IgM seroprelavence and Pupal/Demographic indices of Dengue in Port Sudan city during the period November 2008–October 2009.

Figure 7. Association of meteorological parameters and IgM seroprevalence.

Monthly patterns of meteorological parameters (minimum and maximum temperature and relative humidity), Pupae/person rate and IgM seroprelavence of dengue in Port Sudan city during the period November 2008–October 2009.