Parasite lactate dehydrogenase assay for the determination of antimalarial drug susceptibility of Kenyan field isolates

Background: Researchers have reported that parasite lactate dehydrogenase p(LDH) could be used to determine chemo-sensitivity of plasmodia to compounds with known or presumed antimalarial activities. Objective: To determine the drug sensitivity profiles of field adopted malaria isolates from Kisumu using p(LDH) instead of hapoxanthine assay. Design: Prospective field and laboratory study. Setting: Walter Reed, KEMRI malaria laboratory (Nairobi) and Kisumu District Hospital. Subjects: Twelve field laboratory adopted isolates from Kisumu, five laboratory adopted isolates from other regions in Africa and three reference strains from Walter Reed army Institute of Research, Washington, DC. Results: The p(LDH) enzyme assay was successfully used to measure the IC50 of six antimalarial drugs, chloroquine, quinine, mefloquine, dehydroartemisinin, atovaquone and halofantrine but was not successful with the four other antimalarial drugs, doxycycline, azithromycin, pyrimethamine and sulphadoxine. The Kisumu isolates tested were resistant to chloroquine and mefloquine but sensitive to quinine and the new antimalarial drugs, atovaquone, halofantrine and dehydroartemisinin. Conclusion: The non-radioactive p(LDH) can be used for the determination of drug sensitivity to Kenyan field isolates. It is more suited for use in a resource limited environment and may lead to more judicious prescription of new and more expensive antimalarial drugs and mitigate against the rapid spread of multi-drug resistant parasites in the East African region. East African Medical Journal Vol.82(3) 2005: 119-12

Behavioural determinants of gene flow in malaria vector populations: Anopheles gambiae males select large females as mates

BACKGROUND: Plasmodium-refractory mosquitoes are being rapidly developed for malaria control but will only succeed if they can successfully compete for mates when released into the wild. Pre-copulatory behavioural traits maintain genetic population structure in wild mosquito populations and mating barriers have foiled previous attempts to control malaria vectors through sterile male release. METHODS: Varying numbers of virgin male and female Anopheles gambiae Giles, from two strains of different innate sizes, were allowed to mate under standardized conditions in laboratory cages, following which, the insemination status, oviposition success and egg batch size of each female was assessed. The influence of male and female numbers, strain combination and female size were determined using logistic regression, correlation analysis and a simple mechanistic model of male competition for females. RESULTS: Male An. gambiae select females on the basis of size because of much greater fecundity among large females. Even under conditions where large numbers of males must compete for a smaller number of females, the largest females are more likely to become inseminated, to successfully oviposit and to produce large egg batches. CONCLUSIONS: Sexual selection, on the basis of size, could either promote or limit the spread of malaria-refractory genes into wild populations and needs to be considered in the continued development and eventual release of transgenic vectors. Fundamental studies of behavioural ecology in malaria vectors such as An. gambiae can have important implications for malaria control and should be prioritised for more extensive investigation in the future

Standardizing Visual Control Devices for Tsetse Flies: West African Species Glossina tachinoides, G. palpalis gambiensis and G. morsitans submorsitans

Here we describe field trials designed to standardize tools for the control of Glossina tachinoides, G. palpalis gambiensis and G.morsitans submorsitans in West Africa based on existing trap/target/bait technology. Blue and black biconical and monoconical traps and 1 m2 targets were made in either phthalogen blue cotton, phthalogen blue cotton/polyester or turquoise blue polyester/viscose (all with a peak reflectance between 450–480 nm) and a black polyester. Because targets were covered in adhesive film, they proved to be significantly better trapping devices than either of the two trap types for all three species (up to 14 times more for G. tachinoides, 10 times more for G. palpalis gambiensis, and 6.5 times for G. morsitans submorsitans). The relative performance of the devices in the three blue cloths tested was the same when unbaited or baited with a mixture of phenols, 1-octen-3-ol and acetone. Since insecticide-impregnated devices act via contact with flies, we enumerated which device (traps or targets) served as the best object for flies to land on by also covering the cloth parts of traps with adhesive film. Despite the fact that the biconical trap proved to be the best landing device for the three species, the difference over the target (20–30%) was not significant. This experiment also allowed an estimation of trap efficiency, i.e. the proportion of flies landing on a trap that are caught in its cage. A low overall efficiency of the biconical or monoconical traps of between 11–24% was recorded for all three species. These results show that targets can be used as practical devices for population suppression of the three species studied. Biconical traps can be used for population monitoring, but a correction factor of 5–10 fold needs to be applied to captures to compensate for the poor trapping efficiency of this device for the three species

New enzymatic assay, parasite lactate dehydrogenase in diagnosis of malaria in Kenya

Background: The unique ability of plasmodial lactate dehydrogenase p(LDH) to utilise 3-acetyl pyridine dinucleotide (APAD) in lieu of NAD as a coenzyme in the conversion of pyruvate to lactate, led to the development of a biochemical assay for the detection of plasmodial parasitaemia. Researchers have reported that p(LDH) activity of plasmodia could be used as an assessment of parasitaemia since human red blood cells do not utilise APAD in the metabolism of glucose. Objective: To use p(LDH) for field and clinical diagnosis of malaria in endemic regions of Kenya. Design: Prospective field and clinical study. Setting: Kisumu District Hospital and Walter Reed malaria laboratory in Kenya. Subjects: The study subjects were of three different categories: the healthy non-infected individuals staying out of malaria endemic region (controls group 1), the nonparasitaemic and parasitaemic non- symptomatic healthy individuals living in endemic region {both field study group 2}, the non-parasitaemic and parasitaemic symptomatic individuals living in endemic region {both clinical study group 3}. Results: In the clinical studies, thin smear microscopy gave the highest sensitivity as 75.6% for plasma, while the highest specificity was 71.4%. For red blood cells, the highest sensitivity was 78.4% while specificity was 80%. In the field trials, the highest sensitivity was 89% using thin smear microscopy whereas the specificity was 45% for plasma cut off using thick smear. For red blood cells, the highest sensitivity was 79% while specificity was 66.7%. Conclusion: The variations in sensitivity and specificity of this assay in comparison to microscopy is a strong indication that p(LDH) may be measuring even the sequestered parasites that cannot be visualised by microscopy. The results of this study validates the use of p(LDH) as an alternative objective test for malaria diagnosis against microscopy. East African Medical Journal Vol.82(3) 2005: 112-11

A multivariate analysis of growth and development parameters of the legume pad borer, Maruca testulalis, on variably resistant cowpea cultivars

Principal component analysis was employed to study the variation patterns in 18 cowpea cultivars developed for resistance to Maruca testulalis Geyer (Lepidoptera: Pyralidae) based on 7 developmental parameters of the pest on floral buds, flowers and sliced pods. On the whole, three developmental parameters: percentage pupation (V2), percentage emergence (V5) and growth index (V7) were the most important for the grouping of the cultivars with respect to M. testulalis damage. However, out of the three parameters, growth index (V7) had the highest factor score. Using the cluster analysis technique, the cultivars were sorted into five distinct groups for each part. The importance of these findings in the determination of protection periods for particular cultivars and cultural control studies of M. testulalis in cowpea are discussed

COMPOSITION AND SENSORY QUALITY OF SWEET POTATO CRISPS AS INFLUENCED BY PRE-FRYING TREATMENT

The effect of some pre-frying treatments on the composition and sensory attributes of sweet potato crisps were evaluated. Five pretreatment conditions were studied. Moisture, protein, fat, ash, reducing sugar and vitamin C content of the sweet potato crisps were determined. Sensory attributes of colour, taste, flavor and crispness, as well as overall consumer acceptability of the crisps were analyzed. Pearson correlation coefficient between composition and sensory scores were calculated. Composition of sweet potato crisps varied significantly with pretreatment (p<0.05). Drying pretreatment gave sweet potato crisps with the least moisture and fat contents while blanching gave the highest values. The use of NaCl solution for blanching resulted in a significantly higher value of fat in the crisps. Crisps produced by drying before frying was the most acceptable, although crisps from all the pretreatments were generally acceptable. The lower the moisture, protein and fat content, the higher the acceptability.ª¤

COMPOSITION AND SENSORY QUALITY OF SWEET POTATO CRISPS AS INFLUENCED BY PRE-FRYING TREATMENT

The effect of some pre-frying treatments on the composition and sensory attributes of sweet potato crisps were evaluated. Five pretreatment conditions were studied. Moisture, protein, fat, ash, reducing sugar and vitamin C content of the sweet potato crisps were determined. Sensory attributes of colour, taste, flavor and crispness, as well as overall consumer acceptability of the crisps were analyzed. Pearson correlation coefficient between composition and sensory scores were calculated. Composition of sweet potato crisps varied significantly with pretreatment (p<0.05). Drying pretreatment gave sweet potato crisps with the least moisture and fat contents while blanching gave the highest values. The use of NaCl solution for blanching resulted in a significantly higher value of fat in the crisps. Crisps produced by drying before frying was the most acceptable, although crisps from all the pretreatments were generally acceptable. The lower the moisture, protein and fat content, the higher the acceptability.Â