ABSTRACT
An update of the mosquito fauna of 15 settlement areas in Kaduna metropolis within the Northern Guinea Savannah zone of Nigeria was made from November 2004 - November 2005. Larval samples were obtained and 15 species of mosquitoes identified comprising of the following; Aedes aegypti L, 138 (1.97%), Ae. vittatus Bigot,103 (1.47%), Ae. simpsoni Theobald, 12 (0.17%), Anopheles species, 4 (0.06%); Culex pipiens molestus Forskal, 3307 (47.30%), Cx. pipiens quinquefasciatus Say, 1836 (26.26%), Cx. pipiens pipiens, 456(6.52%), Cx. decens Theobald, 868 (12.42%), Cx. tigripes Grandpre,31 (0.44%), Cx. univittatus Theobald, 34 (0.49%), Cx. horridus Edwards, 115 (1.64%), Cx. musarum Edwards, 40 (0.57%), Cx. nebulosus Theobald, 4(0.06%), Cx. macfei Edwards,41(0.59%), Cx. duttoni, 2 (0.03%). The most abundant species encountered in all the 15 settlements sampled were Culex. p. molestus and Cx. p. quinquefasciatus. Mosquito species bred in eight different sites identified as major breeding habitats in Kaduna metropolis; the proportion of total catch from these habitats is indicated: Concrete gutters (38.23%), Stagnant pool/pond (29.92%), Peridomestic runoffs (PDRF) (22.3.4%), Clay pot (0.86%), Metal containers (0.59%), Abandoned tyres (2.73%), Plastic containers (1.22%) and Roadside potholes (3.61%). Significant difference in breeding populations was noticed among habitats (P=0.024). Concrete gutters, Stagnant pool/ponds and PDRF were encountered in all settlement areas. There was no significant difference in the total mosquito species sampled among the 15 settlements (P=0.436). The old settlement areas had more mosquito species;(13) in comparism to 11 species in the new settlement areas. Diversity in the mosquito species breeding observed during the wet months was significantly higher than those of the dry months (P=0.004); with the highest species diversity of 11 species in August. There was a preponderance of Culex pipiens complex (Cx. p molestus and Cx. p quinquefasciatus) over other mosquito species and this suggests that environmental degradation by human activities associated with rapid urbanization, has provided numerous insanitary breeding habitats for Culicine mosquitoes, particularly Culex. p. molestus and Cx. p. quinquefasciatus.
CHAPTER 1
1.1 Introduction.
Mosquitoes are slender and relatively small, flying insects measuring about 3mm – 6mm in length; although some species can be as small as 2mm –3mm, while others may be as long as 10mm. The body is distinctly divided into head, winged thorax and abdomen (Service, 1980). There are about 3,100 species of mosquitoes belonging to 34 genera, arranged in 3 subfamilies:
Toxorhynchitinae, Anophelinae and Culicinae. The most important human biting species belong to the genera Anopheles, Culex, Aedes, Mansonia, Haemagogus, Sabethes and Psorophora (Service, 1980). Mosquitoes have a worldwide distribution, they occur through out the tropical and temperate regions and extend their range northwards into the Artic circle; the only area from which they are absent is Antartica (Smith, 1978).
Various species from the genera Anopheles, Culex, Aedes, Mansonia, Haemagous and Sabethes are vectors of human diseases, including; malaria, yellow fever, arboviruses, dengue fever and bancroftian filariasis (Johnson, 1979). Mosquitoes are also in themselves a nuisance to humans because of their biting habits and the sound they produce (Gillet, 1971).
Malaria, transmitted by several Anopheles species is probably the most prevalent and devastating disease of mankind in the tropics. The incidence of malaria worldwide is estimated to be between 300 – 500 million clinical cases each year, with about 90% of these occurring in Africa, south of the Sahara – Mostly caused by Plasmodium falciparum. Malaria (either alone or in combination with other diseases) is thought to kill between 1.1 and 2.7 million people worldwide each year; (WHO, 1997; WHO, 2000). Most of these deaths occur in pregnant women, infants or very young children (Lindsay and Marten, 1998; Joana et al., 2001).
Filariasis, although somewhat limited in distribution than malaria, is a common disease in tropical areas. Lymphatic filariasis (elephantiasis) infects about 120 million people in tropical Africa, India, Southeast Asia, the Pacific Island, South and Central America (WHO, 1997). In recent years, this disease has increased because of urbanization, which has created breeding areas for Culex species of mosquitoes that transmit the nematode, Wuchereria bancrofti, that causes lymphatic filariasis, (Rao et al., 1981).
Aedes aegypti, the vector of Yellow fever in urban areas in Africa is wide spread. It was involved in the 1987 yellow fever epidemic, which occurred in Oyo state, Nigeria, causing hundreds of deaths (WHO, 1988).
Dengue fever is the world is most abundant mosquito borne viral disease, transmitted by Aedes aegypti. Over 250 million people worldwide are at risk of infection, coupled with 20 million annual cases in more than 100 countries (WHO, 1997). Mosquito problems and disease transmission in contemporary Africa still presents an unclear picture, especially in sub Saharan African region, where the vector is regarded a major public health factor.
In Nigeria, about 50 million people suffer from malaria annually and the annual death from the disease is estimated to be about 300,000 individuals,
launched on April 25th, 2000 in Abuja Nigeria has as part of its mandate; to develop new tools for the control and eradication of malaria.
Studies have shown that, in villages, towns and cities, the availability of suitable breeding sites for mosquitoes is related to the geographical location, size of human settlement, standard of living, level of education of the inhabitants and other socio-economic factors (WHO, 1980). Despite the past and current control measures, these disease vectors have continued to be a threat to health and socio-economic development, (Bang et al., 1975). In certain developed countries, eradication programme have been achieved, whereas Nigeria and many Africa countries, some level of mosquito control has been achieved by spraying Organochlorines (Dieldrin or BHC) as contact insecticides. (Malaria unit, 1976). However, short-term larval controls with the insecticide-based control programme ended with reports of the development of resistance to insecticides that was reported (Brown and Pal, 1971; Chandre et al., 1999).
1.2 Justification
Nigeria is undergoing rapid urbanization of settlements in areas where only a scattered rural population existed formerly. This has resulted in some areas being densely populated. In such settings, organised sanitary facilities are usually poor; also sewage disposal depends largely upon the initiative of the individual resident. Where water supply is available, there may be drains, soakage pits, peri-domestic run offs and pools of standing water. Domestic conditions like these are
ideal as breeding sites of some common mosquitoes; such as Culex p. quinquefasciatus (Say) (Subra, 1980). The construction of the surface run-off (gutters/culverts), the provision of open or partially covered soakage pits for houses, the excavation pits made and abandoned by the construction companies at construction sites and cement water reservoirs are also likely to create good and active breeding sites for mosquitoes in urban settlements. This is not only an engineering problem but also has major public heath implication.
Some researchers had studied aspects of mosquito ecology; Hanney (1960) did a general survey of the species of mosquitoes in Zaria province, Northern Nigeria, (Kangimi and Kakuri in Kaduna State) between June 1957 to December 1958. The studies revealed Anopheles gambiae (Giles), Anopheles funestus, An. nili (Theo) and An. wellcomei (Theo) were very much present; they constitute the major potential malaria vectors. While the commonest Culicine vectors were Mansonia africana (Theo), and M. uniformis (Theo).
An intensive study on the ecology of Anopheles gambiae s.l by White and Rosen, (1973) in six villages around Kaduna (Kangimi, Rido, Angwan Mua’azu, Sobawa, Nassarawa and Katabu) revealed An. gambiae (83%) and An. arabiensis (17%). Data obtained form a survey (Gadzama, 1977) on the Main campus A.B.U, Samaru, Zaria revealed Anopheline and Culicine mosquito species, with about 96% being Culicines only. Anyanwu et al. (1999) identified 15 species of mosquito from another survey conducted in some parts of Zaira.
In the proposed study area of Kaduna metropolis, the last of these studies done at the proposed study area was by Rishikesh et al. (1985) who studied seasonal variation of Anopheles gambiae and An. arabiensis in Kaduna, some 20
years ago. Therefore the mosquitoes population structure may have changed during the twenty years period; Thus there is still need for the continuous updating of information on the mosquitos and their breeding habitats in Kaduna metropolis in order to contribute to the pool of information necessary for mosquito and malaria control in the fast growing Kaduna town.
1.3 Aim :
This research aimed at identifying the mosquito species and their habitats in Kaduna Metropolis.
Objectives:
1. To determine the species composition in Kaduna metropolis.
2. To determine the mosquito abundance in Kaduna metropolis.
3. To determine the distribution of mosquito species within the settlements.
4. To determine mosquito breeding habitats in Kaduna metropolis.
1.4 Hypothesis:
1. There is no significant difference in the species of mosquito in Kaduna metropolis,
2. There is no significant difference in the abundance of mosquito species in Kaduna metropolis,
3. The distribution of mosquito species is not different between settlements.
4. The breeding habitats of mosquito species in Kaduna metropolis are similar.
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