Acta Troptca, 49(1991)157-163 Elsevier
157
ACTROP 00138
Trial of pyrethroid impregnated bednets in an area of Tanzania holoendemic for malaria Part 3. Effects on the prevalence of malaria parasitaemia and fever E.O. Lyimo 1, F.H.M. Msuya 1, R.T. Rwegoshora 1, E.A. N t c h o l s o n 1'2, A.E.P. Mnzava 1, J.D. Lines 1'1 and C.F. Curtis 2 IAmam Research Centre, Amain, Tanga, Tanzama, and 2London School of Hygtene and Tropical Medtcme, London, U K
(Received 26 July 1990, accepted 30 October 1990) Children aged 1-10 in five wllages were contacted fortnightly Their axlllary temperatures, reports of fevers and blood shdes were taken Following the introduction of permethrln impregnated nets into two estate villages the slide posltlVlty for falclparum malaria dechned markedly In traditional vdlages the introduction of impregnated nets had less convincing effects than in the estate wllages and DDT spraying had no perceptible effect on malaria Over all villages there was a clear relationship between axlllary temperature > 37 4°C, reports of fever and high parasltaemm We defined malaria fever in this way, and found in some cases significant reductions in occurrence of such fever following some time after mtroductmn of permethrm impregnated nets No such effects were found with lambdacyhalothrln nets or with DDT spraying Key words Plasmodmm falctparum, Bednets, impregnated, Malaria morbidity, Shde posltwlty rate
Introduction
E n c o u r a g i n g results were o b t a i n e d m reducing the n u m b e r of infective m o s q m t o bites by the i n t r o d u c t i o n o f i m p r e g n a t e d b e d n e t s or by D D T spraying m five vdlages (Magesa et a l , 1991) However, the test o f whether this was o f a n y h u m a n benefit is whether the prevalence o f dlness due to m a l a r i a was reduced In h o l o e n d e m l c areas, adults build u p a c o n s i d e r a b l e degree of l m m u m t y to malaria, b u t children are m o r e b a d l y affected by the d~sease Even m chddren, there is n o t a simple relationship between Plasmodtum refection a n d dlness In the past there was a t e n d e n c y m m a l a r m e r a d i c a t i o n projects to consider only parasite mfectlon However, recent r e a l s m West Africa (Snow et a l , 1988, C a r n e v a l e et a l , 1988) have considered m a l a r m attacks, a n d we have also m a d e an a t t e m p t to assess dlness due to m a l a r i a by t a k i n g c h d d r e n ' s axdlary t e m p e r a t u r e s a n d e n q u m n g a b o u t recent fevers, before t a k i n g b l o o d shdes Correspondence address C F Curtis, London School of Hygiene and Tropical Medicine, London WC I E 7HT, U K
0001-706X/91/$03 50 © 1991 Elsevter Science Publishers B V
158
Methods The work was carried out in two estate villages, Mllngano and U m b a , with brick houses and tiled roofs, and three tradltmnal villages, K u m b a m t o n l , Mlndu and Mng'aza, with mud houses and thatch roofs (Njunwa et a l , 1991) Children aged 1-10 presenting voluntarily, with or without their parent or guard1an, were met by arrangement in each of the five villages every two weeks A questionnaire was completed, including questions about name, age, use of a bednet, indications of fever during the previous two days, etc The axlllary temperature was taken with an electronic thermometer and a thick blood film was taken if the temperature was > 36 9°C, or if there had been a report of fever In a sample of cases, slides were taken even without these indications The slides were returned to the Ubwarl Field Station, Muheza, stained with Glemsa and examined for malaria parasites The number of parasites per 200 white blood corpuscles was counted The day after taking the slides, the team returned to the village concerned to report the results and to arrange that the children diagnosed as malaria positive received chloroqulne treatment at the nearest Health Centre Seriously 111 patients were transported to the Teule Hospital at Muheza The data from the questionnaires, thermometer readings and blood slides were stored on a computer using a double entry system with cross-checking for data entry errors devised by Miss K Rowan and based on the system which she developed for malaria control trials in The G a m b l a At approximately six-month intervals, mass blood surveys were carried out on as m a n y as possible of the children in each village who were searched for in their homes A slide was taken from each, regardless of whether there were indications of fever
Results and Discussion
Shde postttvtty The upper 2 or 3 hnes in Figs 1 and 2 show the quarterly averages of the percentages of slides from the fortnightly routine surveys which were positive for malaria parasites, almost all of which were P falctparum The lower 2 or 3 lines show the percentages with high parasltaemia ( > 100 parasites/200 w.b c ) The results from the mass surveys ('double' symbols in Fig 1) were generally similar to those shown in the figures for the fortnightly routine surveys Fig 1 indicates that the initial SPR (slide posltlVity rate) was somewhat lower in Mhngano (40-65%) than in U m b a (60-80%) This is probably connected with the better state of the houses at Mhngano making them less favourable for mosquito entry, the lower sporozolte inoculation rate from the mosquito population (Magesa et a l , 1991) and the fact that parents at Mhngano are generally better educated and more likely to treat their children with chloroqulne at the first signs of fever After the introduction of permethrln impregnated nets into Mhngano in September 1987, there was a prolonged downward trend in SPR to a final value of about 20% When permethrln impregnated nets were introduced into U m b a there was a decline in the percentage of children with high parasltaemla (20% to less than 10%) and a slight decline in SPR to 50% Fig 2 shows that the traditional villages of K u m b a m t o n l , Mng'aza and Mlndu
I59 Percent
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100
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60 t
40
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as
Mhngmao
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-0-- Un~ba
Fig I Shdc posltlwty (uppcr pmr o f h n c s ) and pcrcentage o f s h d c s showing high parasltaemla ( > 100/200 w b c , lower pair of hnes) m M h n g a n o and U m b a Blackcned symbols indicate when Impregnated nets were m place The left arrow indicates the time of introduction of p c r m e t h n n lmprcgnatcd nets into M h n g a n o and the right arrow indicates the introduction of slmdar nets into U m b a Percent
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Fig 2 Shde posltwlty (upper hncs) and hlgh parasltaemla (lower hncs) m Mng'aza, Kumbamtom
and
Mmdu Thc leftarrow indlcatcs introductlon of permethrm impregnated nets into Mng'aza the hached arrows mdlcatc D D T spraying m M m d u and the right arrow mdlcatcs mtroductlon of lambdacyhalothrm impregnated ncts into K u m b a m t o m and M 1 n d u
started with very high SPR levels (60-90%) Soon after introduction of permethrm nets into M n g ' a z a there were mdlcat]ons of a dechne m the rate of htgh parasltaemla (from 20% to 5%) and, during 1988, the SPR seemed to be depressed compared with K u m b a m t o m The reduction in SPR was never as convincing as in Mhngano,
160 presumably because the mosquito population and sporozoite inoculation rate remained much higher In Mng'aza than in Mhngano (Magesa et a l , 1991) Differences between Mng'aza and K u m b a m t o n i disappeared when K u m b a m t o n i also received impregnated nets in April 1989 Fig 2 also shows that D D T spraying in Mindu had no apparent Impact on SPR or rate of high parasitaemla After introduction of lamdacyhalothrln impregnated nets in April 1989, the SPR in Mindu declined, and reached the lowest levels recorded In that village (40-50%) in the last two three-month periods of the trial The mosquito population and sporozolte rate was no more strongly reduced by the insecticidal nets than by the D D T spraying (Magesa et a l , 1991) but these parameters do not take into account the personal protection conferred on net users which is not provided by house spraying Fig 3 shows the geometric mean parasite densities in positive slides, in all five villages These show that in Mhngano the nets had a definite Impact on the level of parasltaemla (values in the last year of the trial less than 20/200 w b c ) There are indications of similar effects in the first year after net introduction at Mng'aza and U m b a but at other times and villages, no such effects occurred
Malarza fever Table 1 analyses the computer-stored data from all the villages and 3 age groups on the relationship of reports or measurements of fever to malaria parasitaemla As is well known, temperature fluctuates in malaria patients and our reports of fever were from sources who may have varied in reliability Nevertheless there was a correlation of measured temperature with reported fever - - a m o n g the youngest children with a temperature measured as > 37 4°C there were reports of fever for 64%, but in the same age group with measured axlllary temperature < 37°C reports of fever were made for only 16% The SPR was over 55% in the older children and over 70% in the younger ones Geometric
mean
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(posltlve
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Fig 3 Geometric mean parasitaemlas in positive slides from the fortnightly surveys in all five villages Symbohsm as in Figs 1 and 2
161 TABLE I Relationship, for all villages combined, of parasltaemIa and high parasltaemla ( > 100 parasites/200 w b c ) to axlllary temperature and to reports by the child or guardian that the child had fever d u n n g the preceding two days Slides were taken from almost all the children with temperatures > 36 9°C and/or where fever was reported, but only from a sample of the other children Data are presented for three age groups o f children Fever reported
No
Yes
Temperature
< 37 0
37 0-37 4
> 37 4
< 37 0
37 0-37 4
> 37 4
1862 71 74 24 64
523 70 08 18 73
61 76 67 33 33
354 79 30 31 85
144 79 58 30 38
110 90 91 59 09
2287 66 67 13 33
804 62 64 9 66
85 63 86 20 48
160 66 67 15 56
110 70 00 12 73
60 83 33 45 00
5593 56 21 5 59
1611 59 06 6 53
122 59 02 16 39
263 58 60 13 95
147 58 33 13 89
60 58 33 18 33
Age 1-2 No seen % parasItaemla % high paraslt
Age 3 - 4 N o seen % parasltaemla % high paraslt
Age 5-10 No seen % parasitaemla % high paraslt
even with no sign of fever and this rate was only moderately increased in those with fever However, there was clearer evidence that high parasitaemla caused m a n y of the fevers from which children suffer m these vtllages - - both reported and measured fever correlated with high parasitaemla and in those with reported fever and temperature > 37 4°C the rate of high parasltaemla was several times higher than in those wtthout fever symptoms Thus it was decided to adopt the following criteria for defining a case of malaria fever - - temperature > 37 4°C, and/or reported fever, and parasltaemla > 100/200 w b c Table 2 shows the percentage of children contacted in each village who were diagnosed as having malaria fever in the different phases of the project It is clear that It would have been better if resources had permitted us to have worked in a much larger sample of villages and to use villages, rather than Individual children, as the unit of sampling (Snow et al., 1988, W H O , 1989). Furthermore, between phases 1 and 2, there was a marked increase in the malaria fever rates in the villages of U m b a and K u m b a m t o n l which did not then have nets. This was unfortunately due to the fact that the taking of temperatures had been poorly supervised before this time and often skin contact with the thermometer had not been ensured - inspection of the records revealed a number of instances of implausibly low temperatures recorded To train the team in the correct technique, over a period of several months, a thermometer was used under each armpit and close agreement of the two was required before a record was accepted This poor temperature measurement must also have affected the villages which received nets Table 2 shows that m phase 2 of the trial, whereas the numbers of recorded malaria fever cases increased in the control villages of U m b a and K u m b a m toni, they stayed approximately constant in Mhngano and M n g ' a z a where nets were introduced To test this apparent difference in trend, Bartlett's test was used (Arml-
162 TABLE 2 Percentage of contacts where the chdd was &agnosed as hawng malaria fever, defned as an axdlary temperature > 37 4°C, and/or a report of fever, and with a parasltaemm > 100/200 w b c The number of contacts (N) on which the percentages are based are indicated The table is dwlded into the phases of the trml m which d~fferent vector control measures were introduced Presence of permethrm ~mpregnated nets is indicated by sohd boxes, lambdacyhalothrln nets by boxes with broken hnes and DDT spraying by a double box Phase 1 (Oct'86-Sept'87)
Phase 2 (Oct'87-Mar'89)
Phase 3 (Apr'89-Mar'90) 0 61 [ 819 1
Mhngano
% N
1 94 1444
1 82 2253
Umba
% N
2 80 1206
4 18 1149
Mng'aza
% N
2 19 774
2 68 1118
2 38 359
Kumbamtom
% N
2 83 988
4 40 1204
[4-42~ L 58_~
Mmdu
% N
2 91 996
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Sigmficance tests Factor Permethrm
Vdlage(s)
Phases
Mlmg & Mng vs Umba & Kumb
1 vs 2
/2 2 05 n s
Permethrm
Umba
1 +2 vs 3
Continued progress with perrnethrln
Mhng Mng
2 vs 3 2 vs 3
10 14 (P