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Annals of African Medicine, Vol. 5, No. 1, 2006, pp. 42-45 High Prevalence of Asymptomatic Plasmodium Infection in a Suburb of Aba Town, Nigeria 1R. A. Eke, 2L. N. Chigbu and 3W. Nwachukwu Departments of 1Primary Health Care and, 2Microbiology and Immunology, College of Medicine and Health Sciences, AbiaStateUniversity and 3AbiaStateUniversity Teaching Hospital, Aba, Nigeria Reprint requests to: Dr. Reginald A. Eke, FrankAguMemorialHospital, 21A Park Road, P. O. Box 3309, Aba, Nigeria. E-mail: demregi@yahoo.com Code Number: am06010 Abstract Background:Malaria is endemic in many
parts of the world. Various strategies have been planned to control malaria
from time to time in many places. Whatever may be the strategy the prevalence
of symptomatic and asymptomatic plasmodium parasitaemics has been of prime
importance as useful parameter for its control. It is hoped that malaria
control programme in Nigeria will benefit from prevalence of parasitaemic study
such as this. Key words: Malaria, asymptomatic, control programme Résumé Fond: Le paludisme est endémique dans beaucoup de régions
du monde. De diverses stratégies ont été projetées pour lutter contre le
paludisme de temps en temps dans beaucoup de régions. Quelle que soit la
stratégie, la prévalence du parasitémie symptomatique et asymptomatique de
plasmodium a été d'importance primordiale en tant que paramètre utile pour sa
commande. On l'espère que le programme de lutte contre le paludisme au Nigéria
tirera bénéfice de la prédominance de l'étude parasitémique de ce type. Mots clés: Paludisme, asymptomatique, programme de lutte Introduction Malaria transmission depends on two primary factors. These are location of mosquito breeding sites, and clustering of human habitations where people serving as reservoirs of parasites for mosquito infection live.1 Studies in Senegal and other malaria endemic areas in Africa and other parts of the world have shown high prevalence rate of asymptomatic plasmodium falciparum. 2 The high prevalence provides ready reservoirs of infection making control programme difficult to accomplish. Previous successes in malaria control for example in India and Sri Lanka were primarily attributed to the effects of residual insecticide spraying which severely reduced anopheline population. 3 That coupled with treatment of asymptomatic malaria patients led to the reduction in number of asymptomatic malaria and thus the near elimination of the malaria parasite reservoir. Asymptomatic malaria parasite prevalence knowledge is of prime importance in the control of malaria. Nigeria is matching forward with the roll-back malaria control programme and the study of the degree of prevalence of symptomatic and asymptomatic parasitaemics will help in assessing the level of reservoir of infection. This will influence the necessary programme adjustment to achieve the desired goal. Materials and Method Aba town is made up of two Local Governments-Aba South and Aba North. Aba South, the chosen Local Government has 12 wards out of which ward 3 was chosen. Ward 3 has 16 districts from which one was chosen. The chosen one is at the centre of Ndiegoro flood disaster area. The district was chosen by stratified random selection. The district is in the suburban area of Aba Metropolis. It is an unplanned unsanitary area with almost everything it takes to foster mosquito breeding which include pockets of water, pot-holes, blocked drained and gutter, empty cans, bottles, and receptacles and water bearing plants. The inhabitants are mainly traders and of low income group. About three-quarters of the buildings were not habited as they were submerged at various depths in the flood. The district population was 308 and because of the small population size it was decided to consider the whole 308 for study. The district population was sensitized. It insisted that those found to be parasitaemics whether symptomatic or not should be treated free of charge Despite the sensitization, 25 people refused to participate on religious reasons and 26 people declined for not seeing the importance of the study. Eventually 257 people were those studied. It must be mentioned that the Local Government and the study population gave us their informed consent before we embarked on the study. In compliance with the agreement the study team had with the study population all those found to be parasitaemics were treated with complete doses of 300mg chloroquine base tablets. The children’s dosage of chloroquine was adjusted according to their weight. Medication in all cases was taken before a study team member. Thick and thin smears of blood samples were made from the subjects under study. The smears were taken to a laboratory attached to the district hospital, where they were stained using 2% Giemsa solution for the thick and 100% Leishman solution for the thin film for the identification and speciation of the parasite respectively. The ring forms of the merozoites were identified and counted in 100 filed using x 100 objective lens. The count was done per 200 leucocytes, assuming a leucocyte number of 600/mm3. Individuals who presented with malaria, fever, body pain or headache in addition to microscopy positivity were considered symptomatic. Results The number of subjects studied for the distribution of asymptomatic and symptomatic malaria parasitaemics was 257. The prevalence of asymptomatic and symptomatic parasitaemics by sex is shown in table 1. Out of 117 males examined, 51(43.6%) and 11 (9.4%) were asymptomatic and symptomatic parasitaemics respectively. Also of the 140 females studied, 34 (24.3%) and 20 (14.3%) were asymptomatic and symptomatic parastaemics respectively. A higher distribution of asymptomatic parasitaemics of 51 (43.6%) was noted among males as against females of 34(24.3%), showing a statistically significant difference (p<0.01) using chi-square test. However, a relatively higher distribution of symptomatic parasitaemics among the females of 20(14.3%) was observed as against 11(9.4%) for males. The prevalence of asymptomatic and symptomatic malaria parasitaemics by age is shown in Table 2. The age brackets of 20-39 years and 40-59 years gave almost the same distribution of asymptomatic malaria parasitaemics; 28 (49.1%) and 12 (50%) respectively. The age group 0-4 years gave the least distribution of a symptomatic malaria parasite. A very high distribution of symptomatic malaria parasitaemics 16 (77.3%) was observed in the age group 0-4 years. The distribution of symptomatic malaria parasitaemics got reduced from the ages 15-60 years and above, with the age group 40-59 appearing the least, 1(4.2%). This data showed a statistically significant difference in the age distribution of asymptomatic malaria parasitaemics among the study group (P <0.10) using Chi - square test. Table 1: Sex and prevalence of asymptomatic and symptomatic malaria parasitaemia
Table 2: Age and prevalence of asymptomatic and symptomatic malaria parasitaemia among 257 individuals
Discussion In this study 33.1% of the 257 of the population studied had asymptomatic malaria. That high rate of asymptomatic parasitaemics was almost three folds as much as those with symptomatic infection. This high rate is in line with the findings of other workers in other malaria endemic area.2 The asymptomatic malaria had higher rate of prevalence in males than in females. The difference is statistically significant (p<0.01). The sex difference in the rate may find explanation that the males have more exposure to mosquito biting than the females who at various times in the day may be busy in the warm kitchens of the family. The males may be resting outside being exposed to the mosquito bites. Further work needs to be done to try get to the root of the sex different rate. All age groups should be exposed to plasmodium species and the result in this and other reports 4 confirms this. Although symptomatic malaria is significantly most prevalent in younger age group under 5 years the prevalence of asymptomatic infection is higher in age groups above 5 years. These facts taken together indicate that individuals become immune to malaria as a function of age – function of the number of exposures. Data at table 2 showed a statistically significant difference in the age distribution of asymptomatic malaria parasitaemics among study groups. In Africa, asymptomatic P. falciparum infections are common place and widespread. 5-8 Detection of plasmodium infection by light microscopy is found to be less sensitive than by polymerase chain reaction (PCR). 4 It therefore means that many parasite counts in this study must have been below the microscopic threshold and so many negative cases could have been positive if PCR was the laboratory study method. The implication here is that the rate of parasitaemia in the group studied was definitely very high. There are many more asymptomatic parasitaemics than symptomatic parasitaemics. The asymptomatic parasitaemics are healthy carriers of malaria parasites and serve as reservoir of infection. The symptomatic people can be treated during their clinical manifestation but the asymptomatics remain unnoticed to pose a public health danger to the population as long as there is high mosquito vector density to transmit the parasites. Parasitaemics and in particular asymptomatics are a big threat or challenge to any malaria control programme. For effectiveness, the malaria control programme currently going on in Nigeria and indeed any control programme elsewhere need to take healthy malaria parasite carriers or asymptomatic malaria parasitaemics as reservoirs of infection as serious threat to the success of the programme. The problems it poses needs to be seriously addressed simultaneously with other control strategies. Symptomatic malaria victims can be forced to seek for treatment and from our study findings these are in the minority. That means that the majority of people are public health threat who will continue to be reservoirs of infection and yet have no compulsion to seek for medical treatment. Therefore in any malaria control programme the designers may contemplate including treating the entire population or all the population parasitaemics so as to achieve their desired goal. References
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