Introduction

Developmental projects, such as civil engineering constructions, mining and agricultural projects including deforestation, which are intended to improve the quality of life of the people often bring with it favorable conditions for the breeding of large populations of disease vectors and the associated disease burden. Sharma and Upreathy (1982) observed that dams, lakes, irrigation schemes and other developmental projects though essential for the economic growth of many countries, unfortunately cause increases in malaria and other vector-borne diseases such as filariasis, arboviruses and other health problems. Service (1991) noted that the policy, in the 1970s, of clearing forest in Enugu region of Nigeria for planting of the valuable timber trees, teaks and gmelina, increased the people’s exposure to the bites of forest mosquitoes. He noted that the situation was aggravated as a result of rot holes which developed in the tree stumps left behind after clearing operations which later became filled with water and formed ideal larval habitat for Aedes africanus – a yellow fever vector. WHO (1993) observed that schistosomasis infection has increased over the years due to large scale irrigation projects which created new habitats for the aquatic snails.

The permanent site of Nnamdi Azikiwe University, Awka, in Anambra State of Nigeria is a relatively new project development site. Until March 2006, the institution was located at a temporary site within Awka metropolis but today all the departments have relocated to the permanent site. Most lecture halls, offices, research laboratories and access routes are still under construction. The new site is hitherto uninhabited. It was a vast expanse of agricultural land with such poor topographical features as sluggishly flowing streams, water logged land for the most part of the year, marshy terrain and ground water pools formed by collection of rain water in depressions near and around the hostels, lecture halls and administrative blocks. The land was primarily used for cultivation of rice, maize cassava, yam and vegetables. Wild palm trees and forest galleries punctuate the otherwise derived savannah vegetation. Occasionally monkeys are sited in some parts of the campus. Vectors such as tabanids sometimes fly through the windows into offices and lecture halls. Experience from personal interactions with the students and records from the University Medical Centre indicate that many students complain of malaria and other febrile illnesses suspected to be vector-borne. Large populations of people, students, lecturers, administrative staff, construction staff and people from all walks of life with various interests in the University frequent the campus. The general objective of the study was to investigate the man-biting mosquito species and their breeding sites within the permanent site. The specific objectives were to collect outdoor man-biting mosquitoes using human volunteers (Hbc), collect indoor man-biting mosquitoes using pyrethrum knockdown method (PKC) and finally determine their breeding sites through collection of the immature stages of various mosquitoes breeding around the hostels. The choice of the hostels for study was because only the students in the hostels spend 24 hours daily within the University environment.

Materials and Methods

Study Area

Collection of Outdoor biting mosquitoes

Collection of Indoor biting and resting adult mosquitoes

Collection of Immature stages of mosquitoes

Ethical considerations

Results

A total of 1265 mosquitoes were collected as larvae from different breeding sites around the University hostels (table 1). The mosquitoes collected were A. gambiae 267 (12.12%), A. funestus 71(5.61%), C. quinquefasciatus 466(36.84%), C. tigripes 61(4.82%) and A. aegypti 400(31.62%). A. gambiae was collected from clean rainwater pools in concrete mixer tanks used by the contractors, clean water pools in depressions, potholes and gutters. A. funestus was collected in the same habitats with A. gambiae except the concrete mixer tanks. C. quinquefasciatus was collected in polluted water pools in depressions, pot holes and gutters. C. tigripes was collected in both clean and polluted water pools but not in concrete mixers. A. aegypti was collected in small water holdings in discarded tin cans and depressions.

Seventy-two indoor biting and resting adult mosquitoes were collected inside the 9 rooms selected from the ground, first and second floors of the hostels, (table 2). 33 mosquitoes (45.83%) were collected from the 5 rooms in the ground floor, 35 mosquitoes (48.61%) from three rooms selected from the first floor and 4 mosquitoes (5.56%) from one room selected from the second floor. The different mosquito species collected were A. gambiae 50(69.45%), A. funestus 11(15.27%) and C. quinquefasciatus 11(15.27%). All the three species were collected from the three floors of the hostels. The room density of the mosquitoes was 8 mosquitoes per room. Out of every eight mosquitoes in a room, 6 mosquitoes were A. gambiae while A. funestus and C. quinquefasciatus were 1.2 mosquitoes per room respectively.

A total of 132 outdoor biting adult mosquitoes were collected outside the University hostels between 17 and 20 hours (5.00 – 8.00pm) local time; in three consecutive days using human bait method (table 3). The mosquitoes collected were A. aegypti 67(5.75%), A. albopictus 38(28.79%), A. africanus 11(8.33%), A. taylori 2(1.52%), A. gambiae 8(6.06%). A biting / landing rate of 5.97 mosquitoes per man per hour was observed. Out of every 6 mosquitoes that bit man 3 mosquitoes were A. aegypti, 2 were A. albopictus while others were less than one mosquito/man/hour.

Figure 1

Table 1: Mosquito larvae collected from different breeding sites around the University hostels

Figure 2

Table 2: Indoor-biting and resting adult mosquitoes collected inside the University hostels using pyrethrum knockdown method.

Figure 3

Table 3: Outdoor biting adult mosquitoes collected around the hostels using human bait method

Discussion

The study area which is the University Permanent Site could be considered to be a large development site in a formerly uninhabited area with many buildings and access routes still under construction. This also involved massive ecological changes including deforestation, land excavations and landscaping. Civil engineering constructions including roads frequently create land excavations which fill up with rain water and constitute suitable aquatic habitats for various mosquito species and even snail intermediate hosts of schistosomiasis (Youdeowei & Service, 1986). This probably explains the multiplicity of mosquito breeding sites around the hostels. In addition far-reaching ecological changes in an environment often alter the disease patterns in an area by exposure of the inhabitants to the existing pathogens and vectors or by introducing new diseases and pathogens to the area. The collection of two species of urban mosquitoes namely Aedes aegypti and Culex quinquefasciatus and also Anopheles mosquitoes in a relatively new environment corroborates with the observations of Youdeowei and Service (1986), and hence the complaint of the students. The relocation of the University to its permanent site went with it the movement of large populations of both immune and non-immune individuals into the uninhabited area. The students residing in the University hostels were from diverse environmental conditions and immunological status. This has the public health implication of exposing the students and staff populations to various vectors and vector-borne diseases which they had little or no natural resistance to. Youdeowei and Service (1986) observed that movement of populations to formerly uninhabited areas for agricultural purposes, mineral exploitation or road construction usually expose them to a variety of diseases.

The collection of 1265 mosquitoes as larvae from the different breeding sites around the hostels is an indication of intensive breeding of mosquitoes in the area as well as preponderance of their breeding sites. This finding corroborates with the observations of Mbanugo and Okpalaononuju (2003) who noted that the preponderance of mosquitoes in Awka metropolis was due to prevailing habitats in the area. Five mosquito species including A. gambiae, A. funestus, A. aegypti, C. quinquefasicatus and C. tigripes were collected as larvae from the various breeding sites. Although these mosquitoes breed in stagnant water, they differ in microecological requirements in their breeding habitats. The anopheles group were collected from clean water pools scattered around the hostels, the culex group were collected in polluted water pools whereas the aedes group were collected in small water pools in discarded tin cans and utensils. Their breeding ecology is in tandem with the work of Service (1980).

A. gambiae, A. funestus and C. quinquefasciatus were the three species of man-biting mosquitoes caught indoors, with A. gambiae, 50(69.27%), predominating the collection. Culex and anopheles mosquitoes are night biters and usually enter houses to bite their victims when asleep. Gordon and Lavoipierre (1976) observed that the more important vectors of mosquito-borne diseases are those which show a close association with man and prefer him to other animals as source of food. Service (1980) indicated that adults of A. gambiae are mainly anthropophilic, endophagic and endophilic.

The room density of all the mosquitoes caught indoors is 8 mosquitoes / room/night out of which 5.8 or approximately 6 mosquitoes per room/night were A. gambiae while A. funestus and C. quinquefasciatus were 1.2 mosquitoes/room/night respectively. This suggests that approximately 2 mosquitoes may feed on each student per night as the students are allocated four to a room. Out of the 2 mosquitoes, one must be an anopheles. This is of public health interest because anopheles mosquitoes are very efficient malaria transmitters and can infect many people in a place even at lower densities (Service, 1980).

Six mosquito species namely A. aegypti, A. albopictus, A. africanus, A. taylori, C. quinquefasciatus and A. gambiae were caught biting outdoors around the hostels. With the exception of A. gambiae and C. quinquefasciatus which bite mainly indoors but occasionally bite outdoors, the rest were aedes mosquitoes which are diurnal and crepuscular insects (Onyido et al., 2008). Although these Aedes species bite man, they also indiscriminately bite other animals (Onyido et al., 2006 a, b, Service, 1980).

A biting rate of 5.97 mosquitoes / man / hour was recorded outdoors of which 3.04 mosquitoes/man/hour were A. aegypti while 1.72 mosquitoes / man / hour were A. albopictus. In the presence of yellow fever outbreak in the environment, these biting rates are enough to amplify the spread of the infection (WHO, 1986).

From both larvae and adult mosquito collections, eight mosquito species were collected of which four species were aedes mosquitoes while culex and anopheles mosquitoes had two species each. All the four species of Aedes – A. albopictus, A. aegypti, A. africanus and A. taylori are proven vectors of yellow fever and other arboviruses (Gillet, 1972; Service,1980; WHO, 1986) and all have been variously involved in yellow fever epidemics in Nigeria (Lee and Moore 1972, Lee et al. 1974, Service 1974, Fagbani et al. 1975, Savage et al., 1992).

A. gambiae and A. funestus are important vectors of malaria in Nigeria and sub-Saharan Africa (FMOH, 1990; Ukpai & Ajoku, 2001; Matur et al., 2001). Gordon and Lavoiperre (1976) noted that Anopheles gambiae is an important vector of malaria and filariasis in Africa especially in rural communities. Culex quinquefasciatus is an urban mosquito responsible for transmission of filariasis especially Bancroftian filariasis (Amusan et al., 2003). Culex mosquitoes are not only important transmitters of filariasis but also vectors of several of the mosquito-borne encephalitides (Gordon & Larvoiperre, 1976; Service, 1980).

The present study is of public health concern because the mosquito species collected have been implicated in one type of mosquito- borne disease or the other. The students in the hostels are thus exposed to a variety of mosquito-borne diseases. In addition to advising the students to protect themselves from mosquito bites, organized control strategies should be used to reduce mosquito-man contacts vis-à-vis disease transmission among the students. As many students may not afford the daily use of insecticide aerosols in their rooms, it may be necessary to provide mosquito-net screens on the windows and doors to protect both indigent and well-to-do students from mosquito bites.