Entomological Survey Of Mosquitoes Responsible For The Tranmission Of Lymphatic Filariasis In Three Endemic Villages Of Kano State, Nigeria
M Dogara, H Nock, R Agbede, S Ndams, K Joseph
abundance, endemic, infection rate, infectivity, lymphatic filariasis, mosquito, rate, vector
M Dogara, H Nock, R Agbede, S Ndams, K Joseph. Entomological Survey Of Mosquitoes Responsible For The Tranmission Of Lymphatic Filariasis In Three Endemic Villages Of Kano State, Nigeria. The Internet Journal of World Health and Societal Politics. 2012 Volume 7 Number 2.
Infection by the filarial parasite,
The common clinical manifestations of lymphatic filariasis are acute attacks of adenolymphangitis and disfiguring conditions such as hydrocoele and lymphoedema/elephantiasis (Ahurlu
The World Health Assembly targeted lymphatic filariasis for elimination mainly through a strategy of mass drug administration (MDA) (Abel
Materials And Methods
The Study Area
Kano State is located in the North-western part of Nigeria. The state is situated between latitudes and longititudes, north of the equator and east of Greenwich respectively which is determined as follows: North 100 37, North 100 33, East 70 34 and 90 29 respectively. The State is bordered in the east by Jigawa State, on the west by Katsina State, to the south by Kaduna and Bauchi States. It covers a total area of 20,760 SqKm with 1,754,200 hectares of arable land and 75,000 hectares of forest vegetation and grazing lands. It has an estimated population of about 9,383,332 million people (NPC, 2006).
The state is situated on the Sahel savannah region of West Africa and its climatic condition is tropical having rainy and dry seasons. The length of the wet season is about 100-150 days or five months (from mid-May to mid-October of each year). Rainfall pattern is unimodal; with an average rainfall of 600mm.The dry season lasts for about seven months (from mid-October to mid-May of each year). However, there is the dominance of North Easterly winds, the Harmattan which is cold and dry that extends from November to February of each year. The average maximum and minimum temperature fluctuates throughout the year.
The annual mean ranges from 30C to 35C. High temperatures are recorded during March to May annually while the lowest 13C (sometimes it goes down as low as 10C) is from December to January.
For easy administration the state is divided into 44 local government areas (LGAs). The three LGAs where this study was carried out are Garko located in southern part, Dawakin-Tofa found in the north and Gabasawa in the east.
Survey of Vectors of Lymphatic Filariasis in the Three Villages
The aim of this study is to determine the abundance of the different species of mosquitoes as well as identify the species of mosquito vector(s) responsible for the transmission of lymphatic filariasis in the three villages of Marke, Buda, Gunduwa located in Dawakin-Tofa, Garko and Gabasawa LGAs respectively. These three villages in an earlier study were found to be endemic for lymphatic filariasis with a prevalence of 1.6%.
Collection and Dissection of Mosquitoes
A number of houses in each village were randomly selected for catching and collection of mosquitoes. The purpose of the investigation was explained to the head and members of each of the household selected. Permission to enter each of the household was sought and the right to refuse or withdraw at any time was respected. All catches were done indoors using the Pyrethrum Knock Down (PKD) or Pyrethrum Spray Collection (PSC) methods (Anosike
Collection of the mosquitoes was done after 15minutes by means of a pair of forceps and emptied into labelled Petri-dishes. The date of collection and the number of catches and number of rooms sprayed were recorded for each household in a note book. The prevailing weather conditions at the time of collection and the nature of the settlements as well as activities that favour the breeding of mosquito or otherwise were observed and recorded at the time of collection.
Identification and Dissection of Mosquitoes
The female mosquitoes collected from each household were dissected under a dissecting microscope immediately after collection in the field. A mosquito was placed on the middle of a none-grease slide and identified into genus or species level based on morphological features outlined in Gillett, (1972) under an x40 microscope. The mosquito was separated into head, thorax and abdomen. The head and abdomen were placed on either sides of the slide respectively while the thorax was placed at the middle of the slide. The last two abdominal segments were removed to determine the parity status of the mosquito. The parity status measures whether a female mosquito has completed at least one cycle of reproduction which starts with a blood meal and ends in ovipositoin as against the nulliparous that are yet to lay eggs. Each of the parts was put into a drop of normal saline and squashed by means of the two dissecting pins. The content of the squashed three parts (head, thorax and abdomen) were observed under a light microscope (using x40 objective) for the presence of larval stages L1/L2 and L3 and microfilariae. Identification of the third stage larvae were on the morphological features outline in WHO, (1997b). Observations were carefully recorded in a record book.
The data generated was using simple frequencies and percentages; and then presented in tabular forms. Infection and infectivity rates respectively were calculated using the formulae below:
Collection of Mosquitoes
A total of 1,604 mosquitoes comprising 1,291 females and 513 males were collected from 196 houses in the three villages (Table, I). More mosquitoes were collected in Gunduwa (852 from 105 houses), followed by Marke (448 from 54 houses) and Buda (348 from 37 houses). The overall mean number of mosquitoes caught per house was 8.2; Buda had the highest 9.4, followed by Marke 8.3 and the least was in Gunduwa 8.1. However, the abundance of mosquitoes was observed to depend on the nature of settlements, whether or not animals are reared at the back yard and perhaps the weather prevalent at the time of collection. For example, the high abundance of mosquitoes recorded in Gunduwa was because there is a hamlet, Wailari that has scattered type of settlement and thatched buildings and in most cases animals were raised at the back yards of the houses. In that hamlet alone, 653 mosquitoes were caught from 21 compounds indicating a mean number of mosquitoes per house to be 31 as against 199 mosquitoes from the other four hamlets combined from 84 houses with mean number of mosquitoes caught per house to be 2.3. In Buda, mosquito abundance declined with a break in the rainfall.
Table I: Mosquitoes collected from the study area
Dissection and Identification of Mosquitoes
Of the 1,291 female mosquitoes collected from the three villages, 718 were dissected (Table, II). Only dissected mosquitoes were identified to species level. The parity status of mosquito species composed of 39 nulliparous, 643 gravid and 36 parous. Of the 718 mosquitoes dissected, the most abundant species was Anopheles gambiae, (325) and the least was An. Zimani, (1) (Table, III). Only one mosquito, Culex quinquefasciatus was found to be infected with four larvae (L3) in its thorax at Buda village. The overall infection and infectivity rates were 0.14% and 0.0% respectively. The infection and infectivity rates for Buda where the infection was observed in only one mosquito were 0.7% and 0.0% respectively.
The abundance of mosquitoes, which translates into high or low harvest, was observed to depend on the weather prevalent at the time of collection, the number of houses sampled, the nature of the settlements in the villages and hamlets that make up the villages and animal husbandry practices. High harvest was seen when it rained and in general thatched houses seems to harbour more mosquitoes than unthatched. For instance, Gunduwa village had the highest abundance of mosquitoes because more houses were sampled and the nature of settlements at one of the hamlets, Wailari. The village has scattered type of settlement and majority of the houses are of the thatched type. In addition, animals (cows and goats) are reared at the backyards of most of the houses. The decline in mosquito abundance at Buda was due to a break in rainfall at the time of the mosquito collection. In order of increasing abundance the following mosquitoes were identified and dissected:
In this study, infection was seen in only one
The low infection rate recorded in this study may be because mosquito collection and dissection was not done during the period of peak transmission. It could also be because the prevalence of lymphatic filariasis is low which an indication of light transmission in the villages. In addition, fewer mosquitoes from spray catches would be infective than those from human landing catches as infective larvae are lost during feeding (McMahon
This investigation apart from given an insight into the abundance of mosquito species, has incriminated
The authors are grateful to the Kano State Ministries of Health and Local Government for permission to carry out the work. We also appreciate the support of all the staff of the comprehensive clinics of the three villages, village/ward leaders and the entire people of the three villages where the study was carried out. Financial support in aid of this research by the Management of Federal College of Education, Kano is duly acknowledged.