ABSTRACT
Background: Malaria still remains a life-threatening disease worldwide causing between 190 and 311 million cases of malaria in 2008. Due to the ever increasing resistance to malaria drugs, source reduction has been recognized as a complementary approach to further reduce malaria transmission. Given that the availability of suitable habitats for the oviposition of anopheline mosquitoes increases their breeding and possibly malaria transmission. We proposed that characterizing the breeding site of Anopheles is of major importance for the transition from malaria control to elimination in our study area. However, information on the oviposition sites, characteristics and influencing factors of breeding sites of Anopheles mosquitoes is lacking. This study aimed to determine the preferential oviposition sites, breeding site characteristics and related environmental parameters. Methods: A study was undertaken in Abraka, Delta State to determine the preferential oviposition sites of Anopheles mosquito and characterize such sites. Potential larval habitats that might harbor anopheline immatures were sampled between August and September. The larval sampling was done by the standard dipping method. The habitats were characterized based on substrate type, turbidity, habitat type, algal coverage, canopy coverage, surrounding vegetation, surface debris and distance to the nearest house. A two way analysis of variance (ANOVA) was employed to test for significant difference in the occurrence of anopheline and culicine larvae in the different aquatic habitats sampled. Correlation analysis was used to assess the relationship between the environmental variables and the occurrence of the anopheline larvae in the habitats sampled and also to assess the relationship among the environmental variables examined. Results: A total of 80 aquatic habitats in 8 sites were sampled and 1117 anopheline and 370 culicine larvae were collected. Microscopic identification of the adult Anopheles mosquitoes yielded only Anopheles gambiae. There was no significant difference (P>0.05) in the occurrence of anopheline and culicine larvae in the different habitats sampled, but there was significant difference (P<0.05) for habitat type distribution for anophelines only and culicines only. Correlation analysis revealed that the occurrence of anopheline larvae was correlated with some of the environmental variables examined. Conclusion: The results obtained indicate that Anopheles gambiae prefers open, sunlit and undisturbed habitats for oviposition and that abiotic factors play a vital role in larvae’s habitat preference. Thus such factors should be considered when designing an integrated vector control programs.
ABSTRACT
Aims: To ascertain the gastrointestinal nematode burden on the channids, Parachanna obscura and Parachanna africana (Steindachner, 1879) (Family: Channidae) in the down reaches of Orogodo River at Evboesi and Ekwuoma-Abavo, southern Nigeria and its relationship to the levels of organic pollution. Study Design: A total of 220 channid fish were collected from two stations of the river experiencing different degree of organic pollution and dissected for gastrointestinal nematode parasites Place and Duration of Study: The study lasted for a period of six months (Jan to Jun 2010) with collections of fishes done monthly at two sampling stations of Orogodo River in southern Nigeria. Methodology: A total of 220 channid fishes were examined. Their stomachs and intestines were cut open and the contents were emptied into Petri dishes containing water and were examined for nematode parasites. These were quickly stained with Giemsa stain and viewed under a light microscope. Results: A total of 100 (45.5%) were infected with gastrointestinal nematode parasites. The prevalence of infection reveals that Parachanna obscura recorded 62.5% while Parachanna africana had 66.7% in fishes collected from station 1 and 20.1% and 28.6% respectively from fishes collected at station 2. The nematode parasites recovered were Cucullamus sp., Camallanus sp. and Procamallanus laevionchus. The overall parasitic burden reveals that the prevalence infection was statistically significant (p< 0.05) in the species examined. The distribution of infrapopulations of the parasites varied significantly with size class and weight of the fish peaking in most cases in larger size classes. The chemical parameters of the river water at station 1 showed the water to be stressed with high BOD and nutrients levels when compared with station 2. This may explain the high parasitic burden recorded in the channids at station 1. Conclusion: The intensity of the parasites in the host fish agree with previous hypotheses suggesting that environmental pollution does affect parasite population.