Tanzania Health Research Bulletin Health User's Trust Fund (HRUTF) ISSN: 0856-6496 Vol. 8, Num. 2, 2006, pp. 115-118

Tanzania Health Research Bulletin, Vol. 8, No. 2, May, 2006 pp. 115-118

SHORT COMMUNICATION

L.E.G. MBOERA¹*, L. KADETE², A. NYANGE³ and F. MOLTENI⁴

¹National Institute for Medical Research, P.O. Box 9653, Dar es Salaam, Tanzania
²Regional Medical Officer, Iringa, Tanzania
³Regional Medical Officer, Dodoma, Dodoma
⁴National Malaria Control Programme, P.O. Box 9083, Dar es Salaam, Tanzania

* Correspondence: Dr. Leonard E.G. Mboera; Email: lmboera@nimr.or.tz

Code Number: rb06022

Summary: Cross sectional malaria parasitaemia and entomological surveys were carried out in urban Iringa and Dodoma in Tanzania. A total of 395 and 392 schoolchildren (age range= 6-15 years) were screened for malaria parasites in Iringa and Dodoma, respectively. Plasmodium falciparum was the predominant malaria parasite (Iringa= 100%, Dodoma= 97.8%). Malaria parasitaemia was observed in 14.9% and 12% of the schoolchildren in Iringa and Dodoma, respectively. The geometric mean parasite density for P. falciparum was higher (632 parasites/µl) in Iringa than in Dodoma (74.1 parasites/µl). The average spleen rates were 0.5% and 2% in Iringa and Dodoma, respectively. A slightly higher haemoglobin level was observed among schoolchildren in Dodoma (10.2g/dl) than in Iringa (9.5g/dl). Only a few Anopheles gambiae sensu lato were collected indoors in the two areas. On the average 47.3% and 80% of the children in Iringa and Dodoma, respectively were sleeping under mosquito nets. Although malaria endemicity in the two municipalities is low, unplanned rapid urbanisation is likely to change malaria epidemiology in Tanzania. Continuous malaria and mosquito density surveillance should therefore, form an in integral part of the malaria control strategies in urban areas. Communities should be continuously sensitised to use insecticide-treated mosquito nets and strengthen community-based environmental management to minimise malaria breeding sites.

Key words: urban, malaria, schoolchildren, Tanzania

Malaria is the primary cause of ill health in Africa South of Sahara, causing an enormous health and economic burden. It is estimated that malaria causes up to 500 million-illness episodes and over 1.2 million deaths annually worldwide. More than 90% of these illnesses and deaths occur in Africa South of Sahara, the great majority in children under the age of 5 years (Lopes et al., 2006). In Tanzania, malaria is the leading communicable disease problem, affecting over 95% of the population.

A number of malaria epidemiological studies have been conducted in Tanzania, and mostly covering rural population of northeast and south-east Tanzania. There is a significant lack of knowledge on urban malaria in the country, except for Dar es Salaam and Tanga (Yamagata, 1996; Wang et al., 2006). It is estimated that over 33% of the population in Tanzania live in urban areas (Mbogoro, 2002); this being two-folds the proportion lived in 1978. The rapid urbanization in many areas of the country brings about major changes in ecology, social structure and disease patterns. Such changes are likely to alter the frequency and transmission dynamics of malaria, with significant effects on disease-associated morbidity and mortality. It has been reported that uncontrolled urban population growth accompanied with poor housing and lack of sanitation and drainage of surface water can increase mosquito breeding places and humanvector contact (Keiser et al., 2004). This increase in urban population calls for the attention by health authorities and requires up-scaled and adapted strategies for malaria control and other diseases (Yamagata, 1996; Caldas de Castro et al., 2004).

Data on malaria parasitaemia and transmission in many urban areas of Tanzania is scanty. Such information are urgently required to provide rational basis for the design, implementation and monitoring of malaria control programmes. It was therefore, the objective of this study was to determine malaria prevalence and transmission in two municipalities of Iringa and Dodoma in Tanzania.

This study reports results of malariaometric and entomological surveys carried out in Iringa and Dodoma in March 2001. Iringa Municipality (7º49’S, 35º15’E) lies between 1560 and 2000 m. The area receives an annual rainfall of 750-1000 mm between December and April. The mean temperature is about 19ºC and remains relatively low throughout the year. Chipogoro and Gangilonga areas and their respective primary schools were selected for the study. Dodoma Municipality (6º8’S, 35º45’E) lies at an average altitude of 1100m and receives an annual rainfall of 500mm, with most of the rain falling in November-April. Chinagali School in Chang'ombe-Kati and Mlimani School in Kilimani were selected for the malaria surveys. Gangilonga (Iringa) and Kilimani (Dodoma) were located in well-planned areas, with well built houses and good drainage systems. Chipogoro (Iringa) and Chango'mbe-Kati (Dodoma) were located in areas characterised by poor housing and lack of drainage systems.

Malaria parasitaemia surveys were carried among schoolchildren. Each child was examined clinically and thick and thin blood smears were collected from a finger prick. The blood smears were stained with 10% Giemsa in phosphate buffer (pH 7.2) and examined under a microscope in order to identify any malaria parasite species present. Parasite rate, geometric mean parasite density, gametocyte rates and density indices were then determined. Haemoglobin levels was determined from a sample of 50 schoolchildren in each of the school. Each child screened for malaria parasite was asked whether he/she slept under a mosquito net the previous night.

Entomological surveys were conducted in the same areas where the malariometric surveys were done. Mosquito collections were made using pyrethrum spray catch technique between 06.00 and 09.00hr in 10 houses selected randomly. All mosquitoes collected were morphologically identified, sorted according to site of collection, house, date and species. Female Anopheles gambiae sensu lato and An. funestus were dissected to determine parity by observing the degree of coiling of ovarian tracheoles (Detinova & Gillies, 1964). Salivary glands of parous mosquitoes were examined for malaria parasites using standard dissection techniques (WHO, 1975).

All malariometric and entomological data were entered into EXCEL and Epi-Info 6 and analysed by STATA version 6 (Stata Corporation, USA). Sexual and asexual parasite rates and geometric mean parasite density were then calculated. Assuming an average of 8000 leukocytes per microlitre of blood, the number of parasites/μl was estimated by multiplying by a factor of 40 for asexual forms of malaria parasites.

In Iringa a total of 395 schoolchildren (age range=6-15 years), were screened for malaria parasites. Plasmodium falciparum accounted for 100% of the malaria parasites observed. The overall mean malaria prevalence rate was 14.9% (59/395)(Table 1). Parasite rate was significantly higher among schoolchildren in Ipogoro (19.5%) than Gangilonga (10.3%) (P<0.05). The geometric mean parasite densities were 491 and 773/μl in Ipogoro and Gangilonga, respectively. Gametocytes and spleen enlargement were observed in 0.5% of the children. The haemoglobin levels among schoolchildren in Iringa ranged between 9.3g/dl in Gangilonga and 9.7g/dl in Ipogoro. Among the schoolchildren, 47.3% (187/395) were using mosquito nets. Of these 64.2% were from Gangilonga and 35.8% were from Ipogoro.

In Dodoma a total of 392 schoolchildren (age range= 6-15 years) were screened for malaria parasites of which 12% (47/392) were infected. P. falciparum accounted for 97.8% (46/47) of all species of malaria parasites observed. A mixed infection of P. falciparum + P. malariae was found in one (2.2%) child. The geometric mean of parasite density was slightly higher among schoolchildren in Mlimani (84 parasites/μl) than Chinangali (65 parasites/μl). Gametocytes were observed in 0.76% (3/392) of the children examined. The spleen rate among schoolchildren was slightly higher (3%) in Chinangali than Mlimani (1%). Similarly, the mean haemoglobin level was slightly higher in schoolchildren from Chinangali (10.5g/dl) than Mlimani (9.9g/dl). Twenty-six per cent and 32% of the children in Chinangali and Mlimani, respectively had haemoglobin levels below 10g/dl. On the average 80% of the children in Dodoma were sleeping under mosquito nets.

A total of 665 mosquitoes were collected in Iringa. Of these, 99.4% were Culex quinquefasciatus and An. gambiae s.l + An. funestus accounted for 0.6% of the mosquitoes collected. Only one An. funestus mosquito was collected at Ipogoro. In Dodoma, a total of 229 mosquitoes were collected, of which 171 (74.7%) were caught in Changombe- Kati and 58 (25.3%) in Kilimani. Cx quinquefasciatus accounted for 98.7% and An. gambiae s.l. for 1.3% (3/229) of the total mosquito collection. All the An. gambiae mosquitoes were collected at Kilimani.

Like in many other places in Tanzania, P. falciparum was the predominant species of malaria in Iringa and Dodoma (Mboera, 2000). The mean malaria prevalence rates of 12-14.9%, indicate that the two urban areas are characterised by low malaria transmission. Similar findings have been reported in Iringa town during the 1960s (Clyde, 1967). Higher malaria parasite rates among children have been reported in nearby Iringa Rural district (Lemnge, 1990; Njunwa, 2000; Mboera et al., 2001) and Dodoma Rural district (Clyde, 1967; Irare & Lemnge, 1988; Wakibara et al., 1997).

In Iringa, a significantly higher malaria parasitaemia was observed among schoolchildren in Ipogoro than Gangilonga. However, the difference in parasitaemia between the two study locations in Dodoma was not significant. Some studies have already reported a high degree of heterogeneity in malaria burden in urban environments. It has been observed in Dar es Salaam, that the malaria prevalence rates among schoolchildren were higher as one move from the central to peripheral zones of the city (Yamagata, 1996). This can be explained by the fact that, the peripheral areas, which are usually, with poor drainage, provides much ample breeding sites than the central well-planned parts of towns. Moreover, it has been established that urban malaria prevalence rates show large variation, ranging from as low as 1% in city centres to more that 90% in suburbs. These variations may be attributed to various factors including weather, house locations proximal to wetlands, urban agricultural practices as well as infrastructure, including drainage and type of housing.

The low parasite rates observed in Dodoma could be explained by ecological and climatic difference between the two areas. Dodoma is located in the central plateau characterised by low (500mm) precipitations. Iringa is in the southwestern highlands receiving on average >850mm of rainfall per year. Moreover, findings from this study indicate that there was relatively high mosquito net coverage in Dodoma than in Iringa. However, it could not be established whether or not the nets were treated with insecticides.

In both Iringa and Dodoma, a proportion of schoolchildren were found to have mild to moderate anaemia. Anaemia is a major health problem in Tanzania, especially among young children. The 2004-05 Tanzania Demographic and Health Survey showed that 72% of the children had some level of anaemia. One-fourth of children had mild anaemia, 43% had moderate anaemia, and 4% had severe anaemia (TDHS, 2005). According to TDHS (2005) the prevalence of anaemia in children in Dodoma is 26.1% (mild) and 37.8% (moderate) whereas in Iringa it was 25.1% (mild) and 21.5% (moderate). Previous studies have reported anaemia in 33.8% and 21.3% of the pupils examined at Kikombo and Mlezi (in the suburbs of Dodoma), respectively (Irare & Lemnge, 1988).

Although the number of Anopheles gambiae s.l. during the study period was low, the species is likely to play a major role in malaria transmission in two municipalities. It is likely that few breeding sites for An. gambiae were available at the time of survey and that malaria transmission in the two areas is seasonal, depending on climate. Dodoma region is known for its unstable malaria, a characteristic of semi-arid zones (Mboera, 2004). Iringa at >1560 is also likely to experience seasonal unstable malaria. It has long been known that, in these areas, any change in temperature, relative humidity or rainfall can have a major impact on malaria transmission and possibly leading to epidemics. Constant monitoring of malaria incidence, and mosquito abundance and increased sporozoite rate is therefore, important for early detection of malaria outbreaks.

Rapid urbanisation is likely to change malaria epidemiology in Tanzania. Currently, over one-third of the population lives in urban areas, which are mostly characterised by poor infrastructure and poverty. The increase in malaria incidence at health care facilities and the established malaria endemicity as shown in this study, calls for initiation of effective malaria strategies that are appropriate in urban settings. Continuous malaria and mosquito density surveillance should form an in integral part of the malaria control strategies in such areas. Communities should be continuously sensitised to use insecticide-treated mosquito nets to protect themselves against malaria. Moreover, community-based environmental management to minimise malaria breeding in urban areas should be strengthened.

Acknowledgements

We extend our thanks to the teachers of the schools involved in the study (Ipogoro and Gangilonga in Iringa and Mlimani and Changombe-Kati in Dodoma) for the co-operation and enthusiasm. We are grateful to H. Ndenge, F. Maghondi, E. Thomas,

E. Challo, R. Kihongozi, L. Kisanga and Y. Gwila (Dodoma) and A. Kihatura, F. Mgohamwende, M. Mohamedi, T.M. Kimbe and B. Mkumbwike (Iringa) for their excellent field and laboratory assistance. This study received financial assistance from the Italian Co-operation through the Tanzania Ministry of Health.

References

• Caldas de Castro, M., Yamangata, Y., Mtasiwa, D., Tanner, M., Utzinger, J., Keiser, J. & Singer, B.H. (2004) Integrated urban malaria control: a case study in Dar es Salaam, Tanzania. American Journal of Tropical Medicine and Hygiene 71, 103-117.
• Clyde, D.F (1967) Malaria in Tanzania. London, Oxford University Press.
• Detinova, T.S. & Gillies, M.T. (1964) Observations on the determination of the age composition and epidemiological importance of populations of Anopheles gambiae and Anopheles funestus Giles in Tanganyika. Bulletin of the World Health Organization 30, 23-28.
• Irare, S.G. & Lemnge, M.M. (1988) Malaria and splenomegaly prevalence, haemoglobin status of the population and Plasmodium falciparum response to a number of antimalarials in Dodoma. Annual Report of the National Institute for Medical Research 7, 15-16.
• Keiser, J., Utzinger, J., Caldas de Castro, M., Smith, T.A., Tanner, M. & Singer, B.A. (2004) Urbanization in sub-Saharan Africa and implication for malaria control. American Journal of Tropical Medicine and Hygiene 71, 118-127.
• Lemnge, M.M. (1990) Malaria in underfives and pregnant women in Pawaga, Iringa: In vivo response of Plasmodium falciparum to 4aminoquinolines and pyrimethaminesulfalene (Metakelfin®). Annual Report of the National Institute for Medical Research 9, 21.
• Lopes, A.D., Mathers, C.D., Ezzati, M., Jamison, D.T. & Murray, C.J.L. (2006) Measuring the global burden of disease and risk factors. In: Global Burden of Disease and Risk Factors (eds.
• A.D. Lopes, C.D. Mathers, M. Ezzati, D.T. Jamison & C.J.L. Murray). Oxford University Press and the World Bank.
• Mboera, L.E.G. (2000) Fifty Years of Health Research in Tanzania. An annotated bibliography. 373 pp. DUP (1996) Ltd.
• Mboera, L..E.G. (2004) Environmental and socioeconomic determinants of malaria epidemics in the highlands of Tanzania. Tanzania Health Research Bulletin 6, 11-17.
• Mboera, L.E.G., Kamugisha, M.L., Rumisha, S.F., Kisinza, W.N., Chuwa, G.J., Mkumbwike, B., Khihatura, A., Kadete, L., Mgohamwende, F., Kitua, A.Y. & Molteni, F. (2001) Malaria epidemiological studies in Iringa Rural District, Tanzania. Report submitted to the National Malaria Control Programme, Ministry of Health, Dar es Salaam, Tanzania. June 2001.
• Mbogoro, D.K. (2002) Population Housing Census Results. United Republic of Tanzania. Dar es Salaam.
• Njunwa, K.J. (2000) Intense malaria transmission in Mtera Dam area: need for promoting insecticide treated nets among fishermen, TANESCO staff, and villagers living around the dam. Tanzania Health Research Bulletin 2, (2 Suppl.) 22-23.
• TDHS (2005) Tanzania Demographic and Health Survey 2004-05. National Bureau of Statistics and ORC Macro. Dar es Salaam, Tanzania
• Wakibara, J.V., Mboera, L.E.G. & Ndawi, B.T. (1997) Malaria in Mvumi, central Tanzania and the in vivo response of Plasmodium falciparum to chloroquine and sulfadoxinepyrimethamine. East African Medical Journal 74, 69-71.
• Wang, S.J., Lengeler, C., Mtasiwa, D., Mshana, T., Manane, L., Maro, G. & Tanner, M. (2006) Rapid urban malaria appraisal (RUMA) II: Epidemiology of urban malaria in Dar es Salaam (Tanzania). Malaria Journal 5, 28. doi: 10.1186/1475-2875-5-28.
• WHO (1975) Manual on Practical Entomology in Malaria: Part II - Methods and Techniques. WHO Offset Publications No. 13, Geneva.
• Yamagata, Y. (1996) Final Report of the Japanese International Cooperation Agency (JICA)-Urban Malaria Control Project. Dar es Salaam, Tanzania.

Copyright 2006 - Health User's Trust Fund (HRUTF)

The following images related to this document are available:

Photo images