Permethrin-impregnated bednets are more effective than DDT house-spraying to control malaria in Solomon Islands.

A field trial compared DDT house-spraying with permethrin-impregnated bednets for malaria control in Solomon Islands from 1987 to 1991. Mortality-rates of malaria vector Anopheles farauti in exit window traps were 11.6% from an untreated hut, 10.1% from a hut sprayed with DDT 2 g/m2, and 98% of those from a hut in which the occupants used bednets treated with permethrin 0.5 g/m2. Since bioassays of the DDT-sprayed walls (15 min exposure in W.H.O. standard test cones) gave 77% mortality of An.farauti, it was concluded that the insignificant impact of DDT could be explained by the exophilic behaviour of endophagic vectors, whereas the greater impact of permethrin was attributed to the more effective exposure of An.farauti females to the impregnated bednets-attracted by the occupants. The parous rate was higher indoors, except in the area with permethrin-impregnated bednets. It was therefore concluded that permethrin-impregnated bednets reduced the mean longevity of An.farauti and hence its vectorial capacity. The circumsporozoite (CS) antigen positivity rate of An.farauti in the DDT area was 0.18% outdoors, significantly less than 1.42% indoors. In the comparison area CS rates were 0.65% outdoors and 0.75% indoors. CS antigen was not detected in An.farauti from the bednet area, indicating the apparent prevention of malaria transmission. As DDT spraying was so much less effective, it was discontinued in 1993 and permethrin-impregnated bednets are now the principal malaria control method in Solomon Islands.

The economic impact of Plasmodium falciparum malaria on education investment: a Pacific Island case study.

A small but intensive study was carried out adopting a simple method which attempts to quantify the economic consequences Plasmodium falciparum malaria on education investment through school pupil absenteeism in a community in Solomon Islands. In a randomized sample of 4,920 cases of P. falciparum malaria in a community, 2,886 occurred in children of primary school age group of 7 to 13 years. On average a case gave rise to a mean school absenteeism of 5.3 days. In the final analysis a total of 11,028 pupil days schooling were lost due to the sampled cases of malaria caused by the species. This is equivalent to 55.14 school pupil years as a child is expected to attend school for 200 days in a year. A primary school teacher with an average annual salary of US$3,990.00 is expected to teach 6,500 school pupil days a year. When this is adopted as an economic indicator for investment in education the loss is calculated to be US$6,769.57 or equivalent to US$1.38 per case. When this is applied nationally, assuming that rates are similar for 79,203 cases of P. falciparum reported in 1990, the total consequence for investment in education is US$108,966.00, which is equivalent to 27.31 teachers being paid for not teaching, an unacceptable impact for a small nation like the Solomon Islands.

The effect of permethrin impregnated bednets on the incidence of Plasmodium falciparum, in children of north Guadalcanal, Solomon Islands.

The effect of permethrin impregnated bednets was studied for the first time amongst a large community in North Guadalcanal, Solomon Islands. The community was divided into two; one covered 23 villages with 860 people who were given bednets impregnated at 0.5 g/m2, and the other 20 villages with 520 people was used as control. Parasitological data were collected by regular prevalence surveys and examination of records of malaria patients who have sought treatment in clinics. Entomological data by landing catches using human bait. The entomological results showed a 71% reduction of Anopheles farauti. Even though there was no significant reduction observed with An.punctulatus, as the density was already very low, the number biting indoor was much lower than those outdoor of houses with treated bednets. Parasitologically there was a steady decline in the incidence between surveys with Plasmodium falciparum in the under 10 years old. Even though there was no significant reduction in the other variables measured, there was a steady increase in the clearance rate between surveys which might also be due to easy accessibility to chemotherapy. The study showed the significant beneficial effect of permethrin impregnated bednets, which was found to be still effective up to twelve months, against stable P. falciparum malaria in children.

Seasonal abundance and biting behaviour of Anopheles punctulatus and An. koliensis in Malaita Province, Solomon Islands, and a trial of permethrin impregnated bednets against malaria transmission.

Seasonal abundance of the malaria vectors Anopheles punctulatus Dönitz and An.koliensis Owen in Bilimanu, an isolated inland village with forty-two houses in Malaita Province of the Solomon Islands, was monitored over 28 months by means of all-night landing/biting catches at one site during June 1985 to September 1987. Totals of 1250 An.punctulatus and 141 An.koliensis were collected, the latter being the largest number of this species ever caught at any locality in the Solomons. Bednets impregnated with permethrin 0.5 g/m2 were introduced in December 1986 to be used at night by all 190 villagers for protection against malaria vectors. Bioassay tests with An.punctulatus blood-fed females exposed under nets for 10 min resulted in 100% mortality up to 50 weeks post-impregnation. For An.punctulatus, the main vector species, the mean catch (indoors + outdoors) per man hour was 2.9 (range 0.7-13.2) before a cyclone on 19 May 1986, and, 0.66 (0.2-2.7) after the cyclone. The vector survival rates were usually high before the cyclone, but erratically lower thereafter for An.punctulatus. An.koliensis disappeared after the cyclone. Both An.punctulatus and An.koliensis consistently showed higher rates of biting man indoors than outdoors and their diel biting cycle showed a peak around midnight. Outdoors, the parous proportion of An.punctulatus was twice the nulliparous, and nearly so indoors. Following intervention with permethrin-treated bednets, the mean catch of An.punctulatus fell to 0.35 per man-hour (monthly range 0-1.5). The Plasmodium falciparum malaria infection rate reduced from 10% pre-intervention to zero in September 1987, 9 months after intervention, and then rose again.(ABSTRACT TRUNCATED AT 250 WORDS)

Field evaluation of an insect growth regulator, pyriproxyfen, against Anopheles punctulatus on north Guadalcanal, Solomon Islands.

Five pools containing immature stages of Anopheles punctulatus were treated with pyriproxyfen at 4 different dosages. Inhibition of adult emergence was observed in pupae collected from the test pools and/or those obtained by rearing of the 4th instar larvae. Adult emergence was inhibited completely for 2 months at a dosage of 0.1 ppm, for one month at 0.05 ppm and 0.01 ppm, and for 20 days at 0.02 ppm. Death of test insects were observed at the pupal stage and at adult emergence. The mortality rate at adult emergence increased with the duration of larval rearing and with the elapse of time after application.

Pharmacokinetics of halofantrine and n-desbutylhalofantrine in patients with falciparum malaria following a multiple dose regimen of halofantrine.

Halofantrine is a new blood schizontocidal drug used for the treatment of multidrug-resistant falciparum malaria. The pharmacokinetics of halofantrine (HAL) and its principal metabolite, N-desbutylhalofantrine (BHAL), was investigated in 6 adult male patients of Melanesian origin with uncomplicated falciparum malaria. The patients received 500 mg of halofantrine hydrochloride at times 0, 6 and 12 h (total 1.5 g). All patients responded to treatment with a mean parasite clearance time of 52.7 h and a mean fever clearance time of 33.8 h. The following kinetic parameters (mean values) were determined for HAL and BHAL, respectively: maximum plasma concentration (Cmax) = 896 and 491 ng.ml-1; time to reach the Cmax (tmax) = 15 and 56 h; elimination half-life (t1/2) = 91 and 79 h and the mean residence time (MRT) = 71 and 102 h. Based on the clinical response the plasma concentrations of HAL and BHAL were adequate for the treatment of uncomplicated falciparum malaria in the 6 patients.

Amino acid sequences recognized by T cells: studies on a merozoite surface antigen from the FCQ-27/PNG isolate of Plasmodium falciparum.

Twenty-six overlapping peptides, spanning the entire FCQ-27/PNG sequence of the Plasmodium falciparum antigen known as merozoite surface antigen 2 were screened for their ability to induce the proliferation of peripheral blood lymphocytes (PBL) obtained from 12 donors living in Honiara, Solomon Islands where P. falciparum is endemic. A recombinant (r) form of MSA2, known as Ag 1609 was also screened in these assays and tetanus toxoid (TT) antigen was included as a control. The location of the predicted T cell determinants within MSA2 was examined using the algorithm, AMPHI and by scanning MSA2 for amino acid sequences showing the Rothbard motif. There were 13 predicted amphipathic helical sites and five examples of Rothbard sequences in the antigen. The location of these with regard to the peptides tested is shown. Nine of the 12 individuals responded to TT with high stimulation indices (greater than 4) being obtained in the majority of donors. Only three individuals responded to r-MSA2 with the stimulation indices (SI) in the range of 2.4-4.1. Peptides from both the constant and variable regions of MSA2 were recognized in the proliferative assays. However, the majority of the positive proliferative responses were to peptides which spanned the central variable region which included the two copies of the 32-amino-acid repeat occurring in the antigen. High SI comparable to those obtained to TT were seen in some individuals with some peptides. There was considerable variation between donors in number and nature of the peptides recognised and two donors did not respond to any of the antigens tested. The significance of these findings to vaccine development is discussed.