Seasonal Trends in Epidemiological and Entomological Profiles of Malaria Transmission in North Central Nigeria

Abstract

The influence of seasonal changes on epidemiological and entomological indices of malaria transmission in North Central Nigeria was elucidated in a series of studies carried out between January 2004 and December 2009. The climate in the study area was divided into three seasonal periods namely, rainy (May-October), dry (December-March) and transitional (April and November), during which larval and adult anopheline mosquito collections were carried out and assessed for densities, sporozoite infection and parity rates and potentials for malaria transmission. The results indicated that the climate in the study area was clearly seasonal, with close similarities in the patterns of distribution of the climatic factors in the study sites. Mosquito densities, both at the adult and larval stages (i.e., 29.35 +/- 5.10 adult mosquitoes/man/night and 10.36 +/- 3.34 larvae/dip, respectively), were significantly (p<0.05) highest during the rainy season. However, while the former varied significantly in the three seasonal periods, the latter was not significantly different during the dry and transitional seasons. Malaria transmission risks, in terms of sporozoite rates and entomological inoculation rates, was significantly (p<0.05) least in the dry season (i.e., 2.89 +/- 1.25% and 0.37 +/- 0.21 infective bite/man/night, respectively) but the two variables were not significantly (p>0.05) different during the transitional and rainy seasons. Adult mosquito daily survival rate and adult longevity were least in the dry season (26.52 +/- 11.80% and 6.80 days, respectively) and significantly (p<0.05) highest during the rainy season (72.28 +/- 4.00% and 16.95 +/- 4.20 days, respectively). Parous rates of the mosquitoes and duration of sporogony had distinct distribution pattern from the other variables investigated. While, significantly highest parous rates were recorded in the transitional season (86.00 +/- 4.30%), duration of sporogony was not significantly (p>0.05) different during the three seasons. The epidemiology of urban malaria in North Central Nigeria was discussed from the view points of the these results and concluded that the findings should promote the development of informed temporally-targeted vector control programs for the area.

Seasonal Variations in Frequencies of Acute Vaso-Occlusive Morbidities among Sickle Cell Anaemia Patients in Northern Nigeria

“…Stroke was the least common acute vaso-occlusive morbidity seen in this study. Nonetheless, our data revealed increased frequencies during the rainy season with peak values in July and August, which as earlier highlighted is a period of increased malaria vector breeding and parasite transmission [18,19]. The fundamental pathology of stroke in SCA is initiated by haemolysis induced nitric oxide depletion and vasculopathy leading to narrowing of intracranial arterial vessels that are associated with high flow velocities typically detectable by transcranial Doppler ultrasonography [30].…”

“…The rainy season is associated increased stagnant surface water availability and denser agricultural and non-agricultural vegetations, which are conducive for reproduction and survival of mosquitoes in Nigeria [18]. Consequently, the rainy season is a period of intensification of malaria transmission in Nigeria [19]. In addition, malaria infection had also been reported to be the commonest cause [20].…”

Malariometric Indices among Nigerian Children in a Rural Setting

“…Since there is variability in the sensitivity of these indices, multiple estimates of endemicity should be assessed, and the parameter with the highest prevalence be used to inform decision on interventions. This study was conducted in January which is a relatively low malaria transmission period in the country [26]. Since there is seasonal variability in malaria transmission in the country, reporting on point prevalence of malaria parasitaemia is acknowledged as a limitation of the study in determining the endemicity of the disease.…”

Malaria diagnosis and treatment amongst health workers in University of Nigeria Teaching Hospital Enugu, Nigeria

“…There is a high malaria transmission all year-round, with an average malaria incident rate of 15% during dry season and 35% during wet season. [15,16] Children out-patient's clinic is run in rotation by Resident Doctors in Pediatrics Department. They make use of both the hospital main laboratory and a functional side laboratory in Children's Emergency Room for their investigations.…”