Studies on Mosquitoes Anopheles Species Resting Densities Indoors in Kodok Locality, Upper Nile State, South Sudan (2020-2022).

Studies on Mosquitoes Anopheles Species Resting Densities Indoors in Kodok Locality, Upper Nile State, South Sudan (2020-2022).

Venancio A. Okic

Lecturer at Department of Medical Entomology, Faculty of Public and Environmental Health, Upper Nile University, Malakal, South Sudan.

DOI: https://doi.org/10.51584/IJRIAS.2023.8808

Received: 12 July 2023; Accepted: 14 August 2023; Published: 10 September 2023

ABSTRACT

Malaria is a disease caused by the parasite Plasmodium, which is transmitted by the bite of an infected female anopheles mosquito, only the Anopheles genus transmitted malaria to human. Entomological cross sectional studied carried out  over 24 months, period from April 2020 to March 2022 in four areas of the Kodok locality in Upper Nile State in South Sudan to determine indoor resting density and seasonal changes in indoor resting density, additionally to number of Anopheles and other mosquitoes in a given room by using pyrethrum spray sheet collection for mosquitoes collection Bi-monthly from descriptive household, eighty houses and dipper for larvae collection from eight breeding sites to establish active larvae breeding site patterns, seasonal density and seasonal change in larvae density , morphological identification and sorting out of mosquitoes species according to species morphologically characteristics by using key identification of Gillies and de Meillon 1968.

Total mosquitoes collected were 63644 within eighty houses and identified into species; An. gambiae s.s 68% (43084), An. arabiensis 26% (16840) and other mosquitoes 6% (3720). The density vary between different houses ;  An. gambiae s.s 52-67and An. arabiensis 20-28 in rainy (April to October ) season but in dry season (November to March) An. gambiae s.s  2-12 and An. arabiensis 0-5. During the sampling of mosquitoes larvae, a total number 7704 larva collected; anopheles gambiae 88% (6748) and other mosquitoes 12% (956), within eight potential breeding sites, 384 numbers of visit to sites.

Keywords: Kodok locality, Upper Nile State, South Sudan, An. gambiae s.s, An. arabiensis, anopheles density, other mosquitoes, larva density, seasonal change, seasonal density

INTRODUCTION

Nearly half of the world’s population was at risk of malaria, most cases and deaths occur in sub-Saharan Africa with an estimated 241 million cases and 627 000 deaths, Children under 5 years of age are the most vulnerable group affected by malaria; they accounted for about 80% of all malaria deaths in the WHO African Region (1), Malaria is a disease caused by the parasite Plasmodium, which is transmitted by the bite of an infected female anopheles mosquito (2).

The peak up period of transmission is during the rainy season mainly April to October, P. falciparum is the dominant species of parasite and responsible for more than 90% of the cases in South Sudan (3), Anopheles species are anthropophilic, bite in the morning or evening and at night; others feed during the day, they may bite indoors (endophagic) or outdoors (exophagic) behavior (4).

Population density of this species varies seasonally in relationship to rainfall while population density increases quickly with the first rains and the maximum density is reached at the end of the rainy-season (5). Breeding sites in Kodok locality is driven by predominantly shaded swamp and human-made (waste water) throughout the year however; Anopheles gambiae is considered the main malaria vector in Kodok locality and the most abundant species in larval habitats during both the dry and the rainy seasons while An. gambiae s.s was the principal vector in these areas of the study followed by An. arabiensis which are already found to be involved in malaria transmission in kodok locality as in line with ( 6).

Malaria transmission rates can differ depending on local factors such as rainfall patterns, the proximity of mosquito breeding sites to people, and types of mosquito species in the area. Some regions have a fairly constant number of cases throughout the year; these countries are termed “malaria endemic” in other areas; there are malaria seasons, usually coinciding with the rainy season (7).

MATERIALS AND METHODS

Study Area:

Kodok locality located in Upper Nile State in South Sudan at western bank of White Nile River, The estimate terrain elevation above sea level is 306 meters,  Which lies between latitude 90 53’ 00” N and longitude 32⁰  07’ 00” E and with humidity 49. The population estimated 7,709 according to National Census 2012; the natural vegetation consisted of grasses in swamps, and trees (e.g. Acacia spp)

Figure (1) Map of Upper Nile State Showing fashoda county (Kodok) map with boundaries with other counties (Localities)

Study design:

Cross sectional studied was conducted bi-weekly by using pyrethrum spray sheet collection for mosquitoes collection in eighty   houses in four areas; Hai Bilpam, Hai Ochagi, Hai Nevasha and Hai Salam.

Houses

An eighty houses was been examined /day/section, houses were randomly selected from a random list, choosing a first block follow by the third as follow and within block three houses are selected, first house then the fourth house.

Breeding Habitats:

Larval survey was carried out in eight breeding habitats in the areas to collect larvae from two breeding sites per each area and to investigate the permanent and seasonal ones by using dipper.

Entomological sampling method

Entomology studies were conducted over 24 months period from April 2020 to March 2022 in four areas (Hai Bilpam, Hai Ochugi, Hai Nevasha and Hai Salam) in the Kodok locality, for mosquitoes collection bi-monthly chosen the first and third week each month to surveyed descriptive household by using pyrethrum spray sheet collection for indoor resting, collection started from 7:30 to 11:00 a.m. after consent of house occupant. All mosquito collected species was preserved in paper cups covered with netting for each house and room labeled and mosquitoes’ larvae survey sampled by using dipper in swamp and manmade, at the end all species were Sorting and identifying into species by using key identification of Gillies and de Meillon 1968, Gillies and Goetzee 1987, with light microscope and lens, all anopheles larvae are consider as anopheles gambiae ss.

Data analysis:

was done using Package for the Social Sciences (SPSS, version 16).Descriptive analysis was done to obtain the Means or density and species composition by using ANOVA and Statistical variables investigated were; seasonality (dry versus rainy season) and spatial composition.

RESULT

Distribution and spatial relative abundance of anopheles species in study areas:

The distribution of identified members of the mosquitoes  species by studied sites indicated that total number  63644 mosquitoes identified to species; An. gambiae s.s 68% (43084), An. arabiensis 26% (16840) and other mosquitoes 6% (3720) and after that mosquitoes were sorting in to group according to the areas and species composition Hai Bilpam( An.gambiae s.s 65% , An.  arabiansis 28%),Hai Ochugi (An.gambiae s.s 71%, An.  arabiansis 24%), Hai Salam (An.gambiae s.s 68% , An.  arabiansis 27%) and Hai Nevasha (An.gambiae s.s 68% , An.  arabiansis 26% ) and other mosquitoes species are respectively (7%, 5%, 5%, 6% ). The highest number of An.gambiae s.s is in Hai Ochugi 71% whereas the lowest in Hai Bilpam 65% and An.  arabiansis is the highest in Hai Bilpam 28% whereas the lowest in Hai Ochugi 24% as in table (1) that observed each of the An. gambiae and An. arabiensis was prevalent over the other mosquito’s species in the study area.

The density of anopheles gambiae complex per houses through the year:

The density of anopheles per houses (rooms) during the study period  vary between different houses  An. gambiae s.s 52-67 and An. arabiensis 20-28 in rainy season but in dry season An. gambiae s.s  2-12 and An. arabiensis 0-5 table (2),  An. gambiae predominated comparing to total indoor resting mosquitoes species table (1). These species were most abundant in the rainy season, annual indoor resting density for An. gambiae were 661.19 mosquitoes per house.  The high density in April every year as rain started with anopheles gambiae is a lead through the year.

Total number mosquitoes larvae collected and spatial relative distribution :

during the sampling period April 2020 – March 2022, a total larvae were 7704; anopheles gambiae 88% (6748) and other mosquitoes 12% (956), within 8 potential breeding sites (water locations), 384 number of visits and number of anopheles gambiae was recorded in the different areas of the study; Hai Ochugi 87% (1778), Hai Bilpam 87% (1581), Hai Salam 89% (1942) and Hai Nevasha 87% (1447). Mosquitoes species showed that the locality was infested with Anopheles gambiae s.s 88% and other mosquitoes species 12%. Overall, An. gambiae was the predominant in all breeding sites. The density of anopheles gambiae in swamp is high then waste water during the study period.

Table (1): Number of anopheles mosquitoes collected in indoor resting over 24 months in different four areas.

Other mosquitoes included An. pharoensis .Culex and Aedes.

Table (2): Seasonal change indoor resting density of mosquitoes species over 24 months during rainy and dry season with P-Value:

* Significant different at the 0.05 level.

Table (3): The larvae density of anopheles gambiae at different spatial breeding sites over 24 month.

Waste water: water leaking from tape in distribution point.

Table (4): A total number of anopheles gambiae larvae per location in different breeding site over 24 months.

The high percentage of anopheles gambiae was found in Swamp +waste water.

Figure (1): the composition of An. gambiae s.s and An.arabiensis indoor resting at different areas over 12 months

Figure (2): the species composition at the study sites.

Figure (3): Change in anopheles density per month.

Figure (4): the mean composition of An. gambiae s.s and other mosquitoes species in breeding over 12 months of second year.

DISCUSSION

The findings of this study provide solid data that can make this expectation a reality in Kodok locality and other semi-areas with similar ecological conditions. The abundance of Anopheles species in Kodok locality could be attributed to a number of factors, one of which is that some communities in Kodok locality are located along the bank of White Nile River and it experiences seasonal flooding which usually provides favorable temporary and permanent breeding sites for Anopheles gambiae, as in line with (8).  In the first and the second years which mean over 24 months in different four areas, An. gambiae s.s is generally considered to be an efficient vector, due to its very high number and density indoor resting.

 The result reveal that a number of An. gambiae is high then other mosquitoes species (An funestus, Culex and Aedes) indoor resting which are clear in table (1), Hai Ochugi taken the lead overall in high percentage follow by two areas Hai Salam and Hai Nevash and the lowest is Hai Bilpam , also we can found  Anopheles arabiensis accounted being a second vector along with An. gambiae s.s. as in line with (9).

An. arabiansis have highest number and percentage then other mosquitoes species collected indoor resting in Hai Bilpam ,Hai Salam, Hai Nevasha, Hai Ochugi respectively, and other mosquitoes species take less consideration in number and percentage comparing to An. gambiae s.l in Hai Bilpam, Hai Nevasha respectively and two other areas are equally in number and percentage as in line with (10).

 On the seasonal abundance and density of An. gambiae species have improved understanding on vector and its role in malaria transmission, the result confirmed that density of An. gambiae s.s was influence by rain and increased at the begging of the rainy season between April and September as in figure (4) , as in line with (11), the peak density were observed toward the end of the rainy season, the highest percentage An. gambiae s.s found in Hai Ochugi 71% and An.arabiensis 28%, a competition between different areas  show that the density of An. gambiae s.s rising up during the two seasons dry and rainy in all areas follow by Anopheles arabiensis as in line with (12).

The spatial distribution of An. gambiae was aggregated throughout the year, but the degree of aggregation increased during the rainy season as in line with (13), The high-density houses persisted throughout the season, the high-density houses during the dry season differed from those of the rainy season, Only a few highest-density houses during the dry season persisted across two years, finally, the locations of the hotspots within each period (rainy season, and dry season) were similar between years as in appendix table as in line with (14).

 Results of ANOVA significant differences test showed counts of An. gambiae s.s in Kodok locality are significantly higher in houses especially in areas near to swamp and An. arabiensis follow it, that have relation to long-term contribution to malaria cases, An. gambiae are more important because they have role in malaria transmission.

The availability of permanent water sources complements vector survival by ensuring species that are best Adapted to these kinds of habitats such as members of the Anopheles gambiae are able to breed and sustain malaria transmission.

Large permanent habitats with emergent vegetation are known to favor proliferation of Anopheles, the result showed that the locality was infested with Anopheles gambiae s.s larvae 88% and other mosquitos’ species 12%. , An. gambiae was the predominant in all the population densities of the larvae peaked in April and the lowest larvae densities occurred in November to March.

The Anopheles gambiae s s larvae are the most abundant and most infective breeding site found in kodok locality; in Hai salam have highest percentages then three other areas Hai Nevasha, Hai Ochugi and Hai Bilpam but the lowest percentage of other mosquitoes species found in Hai Salam in all breeding sites as in table (6).

 The density of anopheles gambiae in swamp in three areas are high then waste water during the study period especially in Hai salam and An. gambiae population density per swamp were higher for the all sites, The density of larvae in Swamp Breeding sites can contribute strongly to the adult An. gambiae population density as in line with (15).

Species composition and abundance of mosquitoes larvae are positively identified are Anopheles gambiae s.l constituted high percentage then other mosquitoes species. The study showed that mosquito larvae were abundant after rainy seasons due to the formation of larval habitats, particularly at the edges of White Nile River which served to sustain Anopheles populations during the dry seasons and it was observed that habitats that contained growing grass and other vegetation had more Anopheles larvae than habitats without vegetation as in line with (16).

The mean larval densities were significantly higher in the rainy season than in the dry season, An. gambiae s.s also has wide variations with the highest peaks in April up to September as in line with (17).

Results of ANOVA significant differences test showed counts of late instars of anopheline larvae in Kodok are significantly higher in swamp and lower in waste water in relation to long-term contribution to larval productivity, swamp are  more important because they have water available for anopheline larval development long after most of the other habitats have dried up.

Further effects could have been provided by other permanent water sources located outside the study areas but from where no sampling was carried out, A good example is found in River Nile located less than 1 km away from the furthest breeding site in the three areas; well within the flight range of gravid Anopheles gambiae females as in line with (19).

REFERENCES

1. WHO 2020. Republic of South Sudan. Malaria Indicator Survey (MIS) 2017. https://malariasurveys.org/documents]-  World Health Organization 2020. World Malaria Report 2020.
2. WHO 2016. World malaria report day 2016.Geneva, World Health Organization 2016.
3. (MoH, 2006) Ministry of Health, Government of Southern Sudan. Prevention and treatment guidelines for primary health centres and hospitals. http://www.southernsudanmedicaljournal.com/assets/files/misc/SS_Treatment_Guidelines07.pd
4. Lindsay M. Beck-Johnson, William A. Nelson, Krijn P. Paaijmans, Andrew F. Read, Matthew B. Thomas, Ottar N. Bjørnstad, The Effect of Temperature on Anopheles Mosquito Population Dynamics and the Potential for Malaria Transmission, November 14, 2013
5. Gilles, M.T and De Meillon, B. (1968) .The Anophelinae of Africa South of the Sahara (Ethiopian Zoogeographical Region). South African Inst. Med. Res., Johannesburg.No.54.
6. Atieli et,al 2009. Atieli H, Menya D, Githeko A and Scott T (2009) House design modifications reduce indoor resting malaria vector densities in rice irrigation scheme area in western Kenya. Malaria Journal 8: 108.
7. Precious et.al2017. Precious A. Dzorgbe Mattah1,2*, Godfred Futagbi3, Leonard K. Amekudzi4, Memuna M. Mattah5,Dziedzorm K. de Souza6, Worlasi D. Kartey-Attipoe6, Langbong Bimi3 and Michael D. Wilson6 . Diversity in breeding sites and distribution of Anopheles mosquitoes in selected urban areas of southern Ghana-2017.
8. Mike service, 2004. Medical Entomology for Students, third edition 2004, Cambridge University Press.
9. Roll Back Malaria Partnership 2015. Action and investment to defeat malaria 2016–2030. For a Malaria free World. Geneva: World Health Organization (http://rollbackmalaria.org/files/files/aim/RBM_AIM_Report_A4_EN-Sept2015. pdf, accessed 16 November 2016).
10. Nwabor Ozioma Forstinus, Nnamonu Emmanuel Ikechukwu, Martins Paul Emenike, Odiachi Osita, (2015). Anopheline mosquitoes and the malaria scourge International Journal of Mosquito Research 2015; 2(3): 200-207
11. Atieli et,al 2009. Atieli H, Menya D, Githeko A and Scott T (2009) House design modifications reduce indoor resting malaria vector densities in rice irrigation scheme area in western Kenya. Malaria Journal 8: 108.
12. WHO 2020. Republic of South Sudan. Malaria Indicator Survey (MIS) 2017. https://malariasurveys.org/documents]-  World Health Organization 2020. World Malaria Report 2020.
13. EBENEZER, , NOUTCHA, A. E. M., AGI, P. I.,OKIWELU, S. N. and COMMANDER, T.(2014). Spatial distribution of the sibling species of Anopheles gambiae sensu lato (Diptera: Culicidae) and malaria prevalencein Bayelsa State, Nigeria. Parasites and Vectors, 7(1): 32. doi: 10.1186/1756-3305-7-32.
14. OYEWOLE et.al 2005. OYEWOLE, I. O., IBIDAPO, C. A., ODUOLA, A. O., OBANSA, J. B. and AWOLOLA, T. S. (2005). Anthropophilic mosquitoes andmalaria transmission in a tropical rainforest area of Nigeria. Journal of Life Physical Sciences, 2(1): 6 – 10.
15. Thomson et al. 199. Thomson MC, Connor SJ, Quinones ML et al. (1995) Movement of Anopheles gambiae s.l. malaria vectors between villages in The Gambia. Medical and Veterinary Entomology 9, 413–419.
16. Imbahale et.al 2011.Imbahale SS, Paaijmans KP, Mukabana WR, van Lammeren R, Githeko AK, Takken W. A longitudinal study on Anopheles mosquito larval abundance in distinct geographical and environmental settings in western Kenya. Malar J. 2011;10:81.
17. Precious et.al 2017. Precious A. Dzorgbe Mattah1,2*, Godfred Futagbi3, Leonard K. Amekudzi4, Memuna M. Mattah5,Dziedzorm K. de Souza6, Worlasi D. Kartey-Attipoe6, Langbong Bimi3 and Michael D. Wilson6 . Diversity in breeding sites and distribution of Anopheles mosquitoes in selected urban areas of southern Ghana-2017.
18. Kaufmann et.al 2004. 21. Kaufmann C, Briegel H: Flight performance of the malaria vectors Anopheles gambiae and Anopheles atroparvus. J Vector Ecol 2004,29:140-153