Memórias do Instituto Oswaldo Cruz Fundação Oswaldo Cruz, Fiocruz ISSN: 1678-8060 EISSN: 1678-8060 Vol. 90, Num. 5, 1995, pp. 559-560

RESEARCH NOTE

High Prevalence of Malaria in a Village of the Colombian Pacific Coast

Code Number: OC95112
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Laboratoire de Biologie Parasitaire et de Chimiotherapie, Museum National d'Histoire Naturelle, 61 rue Buffon 75231, Paris cedex 05, France *Departamento de Microbiologia, Facultad de Salud, Universidad del Valle, Cali, Colombia **Instituto de Salud del Pacifico, Av. Simon Bolivar No.17-44, a.a. 20513, Buenaventura, Colombia ***Fundacion FES, Cra 5 No.6-05, a.a. 5744, Cali, Colombia

Key words: Plasmodium falciparum - Plasmodium vivax - Colombia

Very little is known about the present malaria prevalence in the Colombian Pacific coast. In an epidemiological survey made in Cupica (northern part of the Pacific coast), during April 1989, the prevalence of malaria infection was found to be 11.32% of which 87.5% was Plasmodium falciparum, and 12.5% P. vivax (W Rojas et al. 1992 Parasitol Today 8: 141-144). In a study made during one of the peaks of transmission (May-June 1986), in six villages of the Naya river basin, situated in the southern Pacific coast, the survey of parasitemias by thick blood smears revealed a low mean prevalence of 0.95 +/- 1.02%. Among the positive cases, 89.6% were P. falciparum infections, 9.2% were P. vivax and 1.2% were P. malariae or mixed infections (E Sevilla-Casas 1993 Soc Sc Med 17: 1155-1167).

FIGURE

The present study was undertaken during the first two weeks of June 1994, in the village of Zabaletas, located at about 25 km from Buenaventura, the main port of the Pacific coast and not far away from Cupica and from the Naya basin, as shown on the map. Zabaletas is a rural settlement of black autochthonous people with 560 inhabitants belonging to 172 families. The place is surrounded by tropical forest and crossed by a large river. The mean annual temperature is about 28 C and the mean annual rainfall is 7500 mm. Human activities are forest exploitation, fish farming and cultivation of tropical fruits such as banana, chontaduro (Pyrenoglyphis major), borojo (Boroja patinoi) and yucca roots (Manihot spp.).

The study was performed by collecting blood and preparing thick smears which were then stained with Giemsa. Subjects were selected at random, independently on the presence of malaria symptoms, and a total of 318 persons were examined. Smears were considered negative after the examination of one hundred fields.

TABLE Prevalence of malaria in Zabaletas by age, during June 1994

------------------------------------------------------------
                               Age in years
         ---------------------------------------------------
                         0-4   5-9    10    14   >44  Total
------------------------------------------------------------
Persons examined           49   47    68    109   18   318
Positive for malaria 
(%)      12(24.5) 18(22.1) 15(22.1) 17(15.6) 3(16.7) 65(20.4) 
Relative %
of PF
infections                 75    66.7 72.2   70.6  33.1  72.3
Symtomatic Pf
infections                  1     2    0      1      0     4
Symtonmatic Pv
infections                  3     1    0      2      2     8
-------------------------------------------------------------

The blood of 65 persons (20.4%) presented malaria parasites. The distribution among sexes was equal, with 50.8% and 49.2% for women and men, respectively. The analysis of the distribution by age groups, as shown in the Table, indicates that it was homogenous. The malaria prevalence showed a trend to decrease in the groups above 15 years old, but this result was not statisticaly significant (p>0.05, c2 test). The absence of variation in the prevalence of malaria in the different age groups indicates a low level of immunity. The prevalence in the age group 2-9 years was 26.7%, indicating a mesoendemic situation for malaria in this area, according to the Yaounde classification (WHO 1964, Non Serial Publication, WHO Edition, GenIve). 72.3% of positive cases were found to be P. falciparum infections, and 27.7% to be P. vivax infections. The prevalence of symptomatic infections was only 8.5% (4 cases) for P. falciparum , but 44.4% (8 cases) for P. vivax. The very low number of symptomatic cases did not allow a precise analysis of correlation with age. No case of severe malaria was recorded during the survey. Parasitemias in both P. falciparum and P. vivax infections were lower than one parasite per field, except for the following four P. vivax cases: one 7 year old patient presented one parasite per field and three patients presented from two to 20 parasites per field, two of them were 7 years old and one was 40 years old. Therefore, no correlation between the levels of parasitemia and the age could be evidenced.

According to a study on the malaria occurence in the district of Buenaventura (including Zabaletas) during 1987 to 1993, two annual peaks of transmission could be evidenced, in April-May and September-October (F Mendez, JG Carrasquilla, submitted to Colombia Med). The relatively high prevalence of malaria in this area (although it was observed at the end of a period of high transmission) as compared to previous studies performed during a similar period of the year, in neighbouring localities of the Colombian Pacific coast (Rojas et al. loc. cit., Sevilla-Casas loc. cit.) could be due to the specific environmental situation of Zabaletas. Numerous large water tanks are located very close to the village and used for fish breeding. Houses are made of wood and very open in order to provide ventilation due to the high temperature. Use of bednets is not frequent because of economical and cultural reasons. Anopheles nuneztovari is the predominant mosquito species in the village (DPT, unpublished data). The adult mosquito develops its larvae phase in water tanks, and have intra-domiciliary biting habits, as shown by P Fajardo and A Alzate (1987 Colombia Med 18: 14-18). Hence, it is not surprising that transmission of malaria could be frequent in this place, leading to the high prevalence observed in our study. An aditional human risk factor could be trees felling, as A. neivai is also present (DPT, unpublished data), and the abundance of bromeliads in the forest surrounding the village provides an excellent environment for its breeding. Both A. nuneztovari and A. neivai have been demonstrated to be vectors of malaria in the Pacific coast of Colombia (Fajardo, Alzate loc. cit., H Carvajal et al. 1989 Trans R Soc Trop Med Hyg 83: 609). The large predominance of P. falciparum infection appears to be a characteristic of the malaria in the Colombian Pacific coast, as shown in other studies (Rojas et al. loc. cit., Sevilla-Casas loc. cit.). Black people are mostly Duffy negative and it could be the reason for the refractoriness to P. vivax in most of them.

Further studies on the malaria transmission in Zabaletas are required in order to set up a more effective prevention strategy. Curiously, 44% of the P. vivax cases were symptomatic, whereas only 8% of P. falciparum were symptomatic and the four cases of high parasitemia were of P. vivax. Such finding deserve further studies such as the blood typing of the populations specially for the highly susceptible cases of P. vivax infected individuals.

Acknowledgments: to the personel of the Division de Patologias Tropicales (DPT) of Buenaventura for field work and providing entomological data.

Received 30 October 1994

Accepted 31 May 1995

Copyright 1995 Fundacao Oswaldo Cruz

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