Annals of Tropical Medicine & Parasitology
ISSN: 0003-4983 (Print) 1364-8594 (Online) Journal homepage: http://www.tandfonline.com/loi/ypgh19
Malaria in Nigeria: a revisit L. A. Salako, F. O. Ajayi, A. Sowunmi & O. Walker To cite this article: L. A. Salako, F. O. Ajayi, A. Sowunmi & O. Walker (1990) Malaria in Nigeria: a revisit, Annals of Tropical Medicine & Parasitology, 84:5, 435-445, DOI: 10.1080/00034983.1990.11812493 To link to this article: http://dx.doi.org/10.1080/00034983.1990.11812493
Published online: 15 Nov 2016.
Submit your article to this journal
Article views: 2
View related articles
Citing articles: 52 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ypgh19 Download by: [Cornell University Library]
Date: 01 July 2017, At: 04:24
Annals ofTropical Medicine and Parasitology, Vol. 84, No.5, 435-445 (1990)
Malaria in Nigeria: a revisit Bv L.A. SALAKO*
Clinical Pharmacology Unit, University College Hospital, lbadan, Nigeria F. O.AJAYI
Department if Pharmacology, Ogun State University, Sagamu, Nigeria A. SOWUNMI AND 0. WALKER
Clinical Pharmacology Unit, University College Hospital, lbadan, Nigeria Received 4 December 1989, Revised 25 June 1990, Accepted 4 July 1990 The frequency of asymptomatic malaria parasitaemia was investigated in rural and urban schoolchildren aged six to 12 years in southwestern Nigeria between January 1987 and October 1988. Asymptomatic parasitaemia was detected in the rural school-children all year round with the lowest parasite rate in january and the highest injuly, corresponding to the mid-dry and wet seasons respectively. Asymptomatic parasitaemia was also common amongst urban school-children, but the frequency was lower than in the rural children. Parasite density was ,; 1000 !!1- 1 in 42% of parasite-positive asymptomatic children and was > 10 000 !!1- 1 in only 20% of them. Mass treatment with chloroquine, to which the parasites were fully sensitive, was followed by the same rate of re-infection in the parasitepositive and parasite-negative groups. Of7713 patients clinically diagnosed as having malaria 4425 were found to have parasitologicallyproven malaria, and of these 4239 had pure Plasmodium Jalciparum malaria. Of the patients with falciparum malaria only 4·6% were below the age of one year. In 47% the parasite count was ,; 1000 !!1-', and it was over 10 000 !!l- 1 in 37% and over 250 000 !!1- 1 in 16%. There was no significant difference between the asymptomatic children and the acutely ill patients in the percentage with parasite densities ,; 1000 !!1- 1, but the percentage with parasite densities > 10 000 !!1- 1 was significantly greater in the acute malaria patients than in those with asymptomatic parasitaemia.
The epidemiology of malaria in West Africa was extensively studied in the 1950s in response to the need to obtain more information on the disease in that region at the beginning of the malaria eradication era (Bruce Chwatt, 1951a,b; Archibald, 1956; Archibald and Bruce Chwatt, 1956). Although the eradication programme was never prosecuted in West Africa, the information gathered from these studies formed the basis of the control programmes which have been used in the area up to the present time. The striking features of the surveys ofthe 1950s was that malaria in West Africa was uniformly holoendemic in all the countries, and was as much a disease of the urban as it was of the rural areas (Bruce Chwatt, 1951a,b). In spite of marked changes in the ecology and environment since the 1950s which could well have affected vector distribution and behaviour and, therefore, malaria transmission in West Africa, malaria is still controlled there as if the epidemiology described in the 1950s has remained unchanged till the present time. A recent study in The Gambia (Greenwood, 1986) has shown that, in that small country, malaria is now mesoendemic, is seasonal in its occurrence and is relatively rare in urban areas. A re-evaluation of the epidemiology in other countries of the region is therefore indicated. *Address correspondence to: Professor L. A. Salako, Department of Pharmacology and Therapeutics," University ofibadan, Ibadap, Nigeria. 0003-4983/90/050435 +II $03.00/0
© 1990 Liverpool School ofTropical Medicine
436
MALARIA IN NIGERIA
One of the strategies employed by malaria-endem~c countries in Africa to reduce morbidity and mortality is that of treating all cases of pyrexial illness without obvious localizing signs as malaria on the grounds that most of them would have been proved to be malaria if parasitological examination had been done. This assertion has been called to question by several studies in different parts of Africa which have shown that only about 40% of such clinical diagnoses could be confirmed parasitologically (Hendrickse et al., 1971). In spite of these doubts about the rationality of the practice it has continued until now, at least because chloroquine, the drug that is used in treatment, is safe and cheap. However, with the increasing spread and severity of chloroquine resistance in Africa (Fogh et al., 1979; Kyronseppa et al., 1984; Le Bras et al., 1986; Neequaye, 1986; Menon et al., 1987; Oduola et al., 1989), alternative drugs which are more expensive and less safe than chloroquine are now being introduced in control programmes, and this calls for a re-evaluation of the indications for treatment, especially the rationale for treatment without parasitological diagnosis. This paper investigates the prevalence of asymptomatic malaria parasitaemia in primary school children in rural and urban areas of southwestern Nigeria, the influence of mass treatment on re-infection rate, and the frequency of parasitologically-proven malaria in patients clinically diagnosed as having malaria. MATERIALS AND METHODS The study was in two parts; one a study of asymptomatic malaria parasitaemia in primary school children, and the other a study of the prevalence ofparasitologically-proven malaria in hospital patients clinically diagnosed as having malaria when presenting with a pyrexial illness for which no other cause was found.
Study 1 (a) All the 212 children ( 100 boys and 112 girls aged six to 12 years) in a rural area near Lafenwa, Abeokuta, southwestern Nigeria were screened quarterly for malaria parasitaemia over a period of 12 months from January to December 1987. Blood was obtained by finger prick using a disposable stylet. A thick film was made in a standard manner and stained with Giemsa. Microscopic examination was under oil immersion with x 600 magnification. A minimum of 100 oil-immersion fields was examined before declaring a film negative. Species identification showed that approximately 96% of all malaria-positive slides were due to Plasnwdium falciparum. The children were all well at the time of the initial survey in January 1987, and none had an acute illness at any of the three subsequent examinations. (b) Six hundred and forty-four primary school children in urban Abeokuta were similarly screened for malaria parasitaemia on four occasions, in April,June,July and October 1988. Giemsa-stained thick blood films were examined microscopically under oil immersion ( x 600 magnification). Parasite density was determined in P.Jalciparum-positive cases by counting the asexual forms against 1000 leucocytes and assuming a white cell count of6000 J.ll- 1• (c) Three hundred and nine pupils from another urban primary school were studied for the effect of administration of an antimalarial drug on the rate of conversion from negative to positive parasitaemia. The 309 pupils were divided into two groups on the basis of whether they had parasitaemia or not. The parasite-positive group (N = 20) were treated with a single dose of 10 mg kg- 1 chloroquine orally. The parasite-negative group were further subdivided randomly into two subgroups. One subgroup (N = 168) was treated with a single dose oflO mg kg- 1 chloroquine while the other (N= 121) was given a placebo. The three groups were examined for malaria parasitaemia 3, 7, 14, 21, 48,84 and 182 days after treatment. The initial screening and treatment took place in April 1988.
SALAKO ET AL.
437
Study2 The role of malaria in pyrexial illness in the area was investigated by studying the prevalence of malaria amongst a group of patients reporting at the University College Hospital, Ibadan with pyrexia for which there was no immediately obvious cause or localizing sign such as meningitis, pulmonary tuberculosis, measles or bronchopneumonia, and for which the general practitioner had made a diagnosis of malaria. This study took place over a period of32 months from January 1987 to August 1989. The patients were examined for malaria parasitaemia as were the asymptomatic school children. Only those who were slide-positive were finally diagnosed and treated as malaria cases. This diagnosis was kept under review until full recovery by the patient because of the possibility of the parasitaemia being only an incidental finding in a patient suffering from some other disease. Malaria patients were treated with one or other of the following drugs: chloroquine, amodiaquine, sulphadoxine-pyrimethamine, quinine, halofantrine, meftoquine or meftoquine-sulphadoxine-pyrimethamine. A standard follow-up was used. This included examination of thick blood film for malaria parasites every day for seven days and on days 14, 21 and 28 after starting treatment. Patients who failed to respond to any of the first five drugs were retreated with meftoquine. Statistical Analysis Differences between groups were analysed using the l test, and P values < 0·0 1 were taken as significant. RESULTS A marked seasonal variation in the parasite rate was found in the group of212 rural school children screened quarterly for 12 months. The P.jalciparum rate was 3·3% (seven pupils) in January, 13·2% (28 pupils) in April, 74·1% (157 pupils) inJuly and 49·1% (104 pupils) in October (Fig. 1). Only 20 children (9·4%) had no parasite in their blood film on all four occasions that they were examined. One hundred and four (49%) had parasitaemia on one occasion only, 74 (34·9%) had parasitaemia on two occasions, 13 (6·1 %) on three occasions and one person (0·5%) on all four occasions (Fig. 2). The highest quarterly conversion rate from negative to positive parasitaemia (71·7%, 132/184) was found between April and July, followed by 49·1% (27/55) between July and October and 13·2% (27/205) between January and April. Conversion in the reverse direction, from positive to negative parasitaemia, also occurred, and was highest (85·7%) six of seven betweenJanuary and April followed by 51·0 (80/157) betweenJuly and October and 10·7% (3/28) between April andJuly (Table 1). The P. falciparum rate in the 644 urban school children (Table 2) was highest in July (26·5%, N= 171), followed by October (21·4%, N= 138), June (12·9%, N=83) and April (3·1 %, N = 20). Comparison of the parasite rates for the three months (April, July and October) that were common to the two surveys (rural and urban) showed that for each of the three months the parasite rate was significantly lower in the urban than in the rural area (April, l=30·8, P
ISSN: 0003-4983 (Print) 1364-8594 (Online) Journal homepage: http://www.tandfonline.com/loi/ypgh19
Malaria in Nigeria: a revisit L. A. Salako, F. O. Ajayi, A. Sowunmi & O. Walker To cite this article: L. A. Salako, F. O. Ajayi, A. Sowunmi & O. Walker (1990) Malaria in Nigeria: a revisit, Annals of Tropical Medicine & Parasitology, 84:5, 435-445, DOI: 10.1080/00034983.1990.11812493 To link to this article: http://dx.doi.org/10.1080/00034983.1990.11812493
Published online: 15 Nov 2016.
Submit your article to this journal
Article views: 2
View related articles
Citing articles: 52 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ypgh19 Download by: [Cornell University Library]
Date: 01 July 2017, At: 04:24
Annals ofTropical Medicine and Parasitology, Vol. 84, No.5, 435-445 (1990)
Malaria in Nigeria: a revisit Bv L.A. SALAKO*
Clinical Pharmacology Unit, University College Hospital, lbadan, Nigeria F. O.AJAYI
Department if Pharmacology, Ogun State University, Sagamu, Nigeria A. SOWUNMI AND 0. WALKER
Clinical Pharmacology Unit, University College Hospital, lbadan, Nigeria Received 4 December 1989, Revised 25 June 1990, Accepted 4 July 1990 The frequency of asymptomatic malaria parasitaemia was investigated in rural and urban schoolchildren aged six to 12 years in southwestern Nigeria between January 1987 and October 1988. Asymptomatic parasitaemia was detected in the rural school-children all year round with the lowest parasite rate in january and the highest injuly, corresponding to the mid-dry and wet seasons respectively. Asymptomatic parasitaemia was also common amongst urban school-children, but the frequency was lower than in the rural children. Parasite density was ,; 1000 !!1- 1 in 42% of parasite-positive asymptomatic children and was > 10 000 !!1- 1 in only 20% of them. Mass treatment with chloroquine, to which the parasites were fully sensitive, was followed by the same rate of re-infection in the parasitepositive and parasite-negative groups. Of7713 patients clinically diagnosed as having malaria 4425 were found to have parasitologicallyproven malaria, and of these 4239 had pure Plasmodium Jalciparum malaria. Of the patients with falciparum malaria only 4·6% were below the age of one year. In 47% the parasite count was ,; 1000 !!1-', and it was over 10 000 !!l- 1 in 37% and over 250 000 !!1- 1 in 16%. There was no significant difference between the asymptomatic children and the acutely ill patients in the percentage with parasite densities ,; 1000 !!1- 1, but the percentage with parasite densities > 10 000 !!1- 1 was significantly greater in the acute malaria patients than in those with asymptomatic parasitaemia.
The epidemiology of malaria in West Africa was extensively studied in the 1950s in response to the need to obtain more information on the disease in that region at the beginning of the malaria eradication era (Bruce Chwatt, 1951a,b; Archibald, 1956; Archibald and Bruce Chwatt, 1956). Although the eradication programme was never prosecuted in West Africa, the information gathered from these studies formed the basis of the control programmes which have been used in the area up to the present time. The striking features of the surveys ofthe 1950s was that malaria in West Africa was uniformly holoendemic in all the countries, and was as much a disease of the urban as it was of the rural areas (Bruce Chwatt, 1951a,b). In spite of marked changes in the ecology and environment since the 1950s which could well have affected vector distribution and behaviour and, therefore, malaria transmission in West Africa, malaria is still controlled there as if the epidemiology described in the 1950s has remained unchanged till the present time. A recent study in The Gambia (Greenwood, 1986) has shown that, in that small country, malaria is now mesoendemic, is seasonal in its occurrence and is relatively rare in urban areas. A re-evaluation of the epidemiology in other countries of the region is therefore indicated. *Address correspondence to: Professor L. A. Salako, Department of Pharmacology and Therapeutics," University ofibadan, Ibadap, Nigeria. 0003-4983/90/050435 +II $03.00/0
© 1990 Liverpool School ofTropical Medicine
436
MALARIA IN NIGERIA
One of the strategies employed by malaria-endem~c countries in Africa to reduce morbidity and mortality is that of treating all cases of pyrexial illness without obvious localizing signs as malaria on the grounds that most of them would have been proved to be malaria if parasitological examination had been done. This assertion has been called to question by several studies in different parts of Africa which have shown that only about 40% of such clinical diagnoses could be confirmed parasitologically (Hendrickse et al., 1971). In spite of these doubts about the rationality of the practice it has continued until now, at least because chloroquine, the drug that is used in treatment, is safe and cheap. However, with the increasing spread and severity of chloroquine resistance in Africa (Fogh et al., 1979; Kyronseppa et al., 1984; Le Bras et al., 1986; Neequaye, 1986; Menon et al., 1987; Oduola et al., 1989), alternative drugs which are more expensive and less safe than chloroquine are now being introduced in control programmes, and this calls for a re-evaluation of the indications for treatment, especially the rationale for treatment without parasitological diagnosis. This paper investigates the prevalence of asymptomatic malaria parasitaemia in primary school children in rural and urban areas of southwestern Nigeria, the influence of mass treatment on re-infection rate, and the frequency of parasitologically-proven malaria in patients clinically diagnosed as having malaria. MATERIALS AND METHODS The study was in two parts; one a study of asymptomatic malaria parasitaemia in primary school children, and the other a study of the prevalence ofparasitologically-proven malaria in hospital patients clinically diagnosed as having malaria when presenting with a pyrexial illness for which no other cause was found.
Study 1 (a) All the 212 children ( 100 boys and 112 girls aged six to 12 years) in a rural area near Lafenwa, Abeokuta, southwestern Nigeria were screened quarterly for malaria parasitaemia over a period of 12 months from January to December 1987. Blood was obtained by finger prick using a disposable stylet. A thick film was made in a standard manner and stained with Giemsa. Microscopic examination was under oil immersion with x 600 magnification. A minimum of 100 oil-immersion fields was examined before declaring a film negative. Species identification showed that approximately 96% of all malaria-positive slides were due to Plasnwdium falciparum. The children were all well at the time of the initial survey in January 1987, and none had an acute illness at any of the three subsequent examinations. (b) Six hundred and forty-four primary school children in urban Abeokuta were similarly screened for malaria parasitaemia on four occasions, in April,June,July and October 1988. Giemsa-stained thick blood films were examined microscopically under oil immersion ( x 600 magnification). Parasite density was determined in P.Jalciparum-positive cases by counting the asexual forms against 1000 leucocytes and assuming a white cell count of6000 J.ll- 1• (c) Three hundred and nine pupils from another urban primary school were studied for the effect of administration of an antimalarial drug on the rate of conversion from negative to positive parasitaemia. The 309 pupils were divided into two groups on the basis of whether they had parasitaemia or not. The parasite-positive group (N = 20) were treated with a single dose of 10 mg kg- 1 chloroquine orally. The parasite-negative group were further subdivided randomly into two subgroups. One subgroup (N = 168) was treated with a single dose oflO mg kg- 1 chloroquine while the other (N= 121) was given a placebo. The three groups were examined for malaria parasitaemia 3, 7, 14, 21, 48,84 and 182 days after treatment. The initial screening and treatment took place in April 1988.
SALAKO ET AL.
437
Study2 The role of malaria in pyrexial illness in the area was investigated by studying the prevalence of malaria amongst a group of patients reporting at the University College Hospital, Ibadan with pyrexia for which there was no immediately obvious cause or localizing sign such as meningitis, pulmonary tuberculosis, measles or bronchopneumonia, and for which the general practitioner had made a diagnosis of malaria. This study took place over a period of32 months from January 1987 to August 1989. The patients were examined for malaria parasitaemia as were the asymptomatic school children. Only those who were slide-positive were finally diagnosed and treated as malaria cases. This diagnosis was kept under review until full recovery by the patient because of the possibility of the parasitaemia being only an incidental finding in a patient suffering from some other disease. Malaria patients were treated with one or other of the following drugs: chloroquine, amodiaquine, sulphadoxine-pyrimethamine, quinine, halofantrine, meftoquine or meftoquine-sulphadoxine-pyrimethamine. A standard follow-up was used. This included examination of thick blood film for malaria parasites every day for seven days and on days 14, 21 and 28 after starting treatment. Patients who failed to respond to any of the first five drugs were retreated with meftoquine. Statistical Analysis Differences between groups were analysed using the l test, and P values < 0·0 1 were taken as significant. RESULTS A marked seasonal variation in the parasite rate was found in the group of212 rural school children screened quarterly for 12 months. The P.jalciparum rate was 3·3% (seven pupils) in January, 13·2% (28 pupils) in April, 74·1% (157 pupils) inJuly and 49·1% (104 pupils) in October (Fig. 1). Only 20 children (9·4%) had no parasite in their blood film on all four occasions that they were examined. One hundred and four (49%) had parasitaemia on one occasion only, 74 (34·9%) had parasitaemia on two occasions, 13 (6·1 %) on three occasions and one person (0·5%) on all four occasions (Fig. 2). The highest quarterly conversion rate from negative to positive parasitaemia (71·7%, 132/184) was found between April and July, followed by 49·1% (27/55) between July and October and 13·2% (27/205) between January and April. Conversion in the reverse direction, from positive to negative parasitaemia, also occurred, and was highest (85·7%) six of seven betweenJanuary and April followed by 51·0 (80/157) betweenJuly and October and 10·7% (3/28) between April andJuly (Table 1). The P. falciparum rate in the 644 urban school children (Table 2) was highest in July (26·5%, N= 171), followed by October (21·4%, N= 138), June (12·9%, N=83) and April (3·1 %, N = 20). Comparison of the parasite rates for the three months (April, July and October) that were common to the two surveys (rural and urban) showed that for each of the three months the parasite rate was significantly lower in the urban than in the rural area (April, l=30·8, P
