A genus- and species-specific nested polymerase chain reaction malaria detection assay for epidemiologic studies.

A nested polymerase chain reaction (PCR) assay that uses Plasmodium genus-specific primers for the initial PCR (nest 1) amplification and either genus- or species-specific primers for the nest 2 amplifications was tested on laboratory and field samples. With in vitro cultured Plasmodium falciparum-infected blood samples, it was capable of detecting six parasites/microl of blood using DNA prepared from 25-microl blood spots on filter paper. The assay was evaluated on fingerprick blood samples collected on filter paper from 129 individuals living in a malaria-endemic area in Malaysia. Malaria prevalence by genus-specific nested PCR was 35.6% (46 of 129) compared with 28.7% (37 of 129) by microscopy. The nested PCR detected seven more malaria samples than microscopy in the first round of microscopic examination, malaria in three microscopically negative samples, six double infections identified as single infections by microscopy and one triple infection identified as a double infection by microscopy. The nested PCR assay described is a sensitive technique for collecting accurate malaria epidemiologic data. When coupled with simple blood spot sampling, it is particularly useful for screening communities in remote regions of the world.

Chemotherapeutic malaria control as a selective primary health care activity in the Solomon Islands.

Malaria control by chemotherapy has been established in rural villages of Guadalcanal, the Solomon Islands, following field trials. As a selective primary health care activity, mobile unit teams visited villages once or twice a year to detect malaria positives and gave chloroquine and primaquine to treat the infection and interrupt the transmission. On site diagnosis was by the use of acridine orange fluorescent staining or the ICTPf commercial diagnostic kit. To avoid possible haemolytic crises, a new single step screening method of G6PD deficiency was introduced. This approach has been accepted well by villagers and proved to be an efficient and feasible control method even in remote rural villages with endemic malaria transmission. Epidemiological modelling of the situation predicts reduction of prevalence in five years.

Humoral immune responses of Solomon Islanders to the merozoite surface antigen 2 of Plasmodium falciparum show pronounced skewing towards antibodies of the immunoglobulin G3 subclass.

The immunoglobulin G (IgG) subclass distribution of antibodies to merozoite surface antigen 2 of Plasmodium falciparum in Solomon Islanders showed marked skewing towards the IgG3 subclass. This was not observed with crude P. falciparum schizont antigen. IgG3 responses may be short-lived and require repeated restimulation for their maintenance. This may be provided by persistent infection (premunition) or new infections.

Relationship of haptoglobin polymorphism to malaria in the Solomon Islands.

Haptoglobin (Hp) polymorphism and its relationship to malaria infections was examined in Solomon Islanders under 25 years of age. The slide positive rate for malaria was 48% (53/111): Plasmodium vivax (Pv) 21 cases, Plasmodium falciparum (Pf) 16 cases and the remaining 16 were a mixture of Pv/Pf/P. malariae. Of 111 subjects examined, 17% (19 subjects) were ahaptoglobinemic (HpO). No association was observed between HpO and parasitemia, gender, anemia, serum insulin-like growth factor-1 (IGF-1) level, blood glucose level and enlargement of the spleen. These results suggest that malaria may not be the major cause of HpO in the people of the Solomon Islands.

Prevalence of malaria and its relationship to anemia, blood glucose levels, and serum somatomedin c (IGF-1) levels in the Solomon Islands.

As part of establishing effective methods for malaria control, the malaria-associated nutritional status was surveyed on Guadalcanal Island in the Solomon Islands in 1993. A total of 506 residents participated in this study. The slide positive rate for malaria was 54% (275/506) in all ages, with a high of 79% for children aged 4-6 years. Plasmodium falciparum was the most common species (52%), followed by P. vivax (29%). Splenomegaly in children from infants to age 15 was detected at the rate of 30% (104/343) by the palpation method. Body mass index was lower in Solomon Islanders than for the Japanese population up to 15 years old in both genders. Mean values for serum insulin-like growth factor-1 (IGF-1) were also lower in Solomon Islanders in children under 18 years old. The hemoglobin distribution curves were almost identical in the malaria-positive (P(+)) and -negative (P(-)) groups. The percentage of cases with less than 80 mg/dl of blood glucose and those with less than 50 ng/ml of IGF-1 were higher in the P(+) group than for the anti-malaria drug-untreated malaria-negative (P(-)D(-)) group. It is suggested that low blood glucose and low IGF-1 levels may have some relationship with the malaria infection.

Plasmodium falciparum genetic diversity can be characterised using the polymorphic merozoite surface antigen 2 (MSA-2) gene as a single locus marker.

The genetic diversity of Solomon Island Plasmodium falciparum isolates was examined using MSA-2 as a single locus marker. Amplification of MSA-2 gene fragments showed size polymorphism and the presence of mixed infections. Sequence analysis indicated a global representation of MSA-2 alleles with representatives of 3D7/CAMP allelic subfamilies and the FCQ-27 allelic family being identified. A simplified method of characterisation, utilising PCR-RFLPs of MSA-2 gene fragments, was developed. The RFLPs allowed identification of allelic families and further distinction within the 3D7/CAMP family. The amplification of MSA-2 gene fragments from culture derived lines revealed a loss of diversity for a number of Solomon Island isolates. Genomic diversity was confirmed for Solomon Island lines, along with Papua New Guinean and Thai lines, by the generation of 7H8/6 fingerprints. All lines were distinct and band sharing frequencies and Wagner tree construction failed to identify any geographic clustering.

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.