Browsing by Author "Maharaj, Rajendra."

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Effects of temperature on members of the Anopheles gambiae complex (Diptera: Culicidae) in South Africa : implications for malaria transmission and control.
(1996) Maharaj, Rajendra.; Appleton, Christopher Charles.; Le Sueur, David.
This study investigated the effects of temperature and relative humidity (both controlled and natural) on the lifecyle and morphology of adults of members of the Anopheles gambiae complex in northern KwaZulu-Natal, South Africa. Laboratory investigations into the effects of simulated temperature and relative humidity regimes concentrated on seasonal differences in longevity, egg hatchability, reproductive potential and adult survivorship of An. arabiensis. Differences were found in the life table parameters when these mosquitoes were reared under conditions of seasonal temperature and relative humidity. During the cool season the lifespan and adult survivorship of mosquitoes were greater than those reared during the warm season. In summer, the egg hatchability and reproductive potential were greatest whereas in winter An. arabiensis underwent gonotrophic dissociation although these females were found to take blood meals readily. The influence of seasonal temperature and relative humidity on the body size of An. arabiensis was investigated, both in the laboratory and under field conditions. In both environments, these factors were found to significantly influence body size. In winter, there was a 13% increase in wing size compared to summer bred mosquitoes. A comparison of body size of An. arabiensis, An. merus and An. gambiae reared under laboratory conditions of seasonal temperature and relative humidity showed that the wing size of An. arabiensis was greater than that of An. merus and An. gambiae. The effect of temperature and relative humidity on morphological criteria used in species separation was also investigated. Seasonal differences in wing spot size were compared for An. arabiensis, An. merus and An. gambiae. From this investigation it was concluded that the pale and dark spots on the wing of Anopheles mosquitoes could not be used in species identification due to the large degree of inter-species overlap in the wing spot measurements. The measurement of the pale band at the junction of the 3rd and 4th tarsomere on the hind leg was also investigated for its use in species separation and were found to be useful within the An. gambiae complex. The implications of this study on the transmission and control of malaria are discussed with reference to the late season transmission during March to May that is characteristic of the region.
An investigation into the robustness of insectary-reared Anopheles Arabiensis for use in the Sterile Insect technique for controlling malaria.
(2018) Manilal, Yurita Yona.; Olckers, Terence.; Maharaj, Rajendra.
Human malaria is one of the deadliest vector-borne diseases in the world and is caused by parasites of the genus Plasmodium that are transmitted via mosquitoes of the genus Anopheles. The highest impact of malaria can be seen in Africa, where 90% of worldwide deaths occur. Although current vector control strategies include biological control, chemical application and environmental management, there is renewed interest in the Sterile Insect Technique (SIT). SIT involves the mass production of the target population, in this study Anopheles arabiensis Patton, sterilizing the males with ionizing radiation and, thereafter, the mass release of these sterile males into the natural environment. The subsequent mating of the sterile males with the wild females should result in a decrease, and ultimately the elimination, of the natural An. arabiensis population. However, for SIT to be successful, the insectary-reared males need to compete effectively with their wild counterparts for female insemination. This study was conducted to determine if the laboratory-reared males would be able to compete successfully with the wild male population in northern KwaZulu-Natal. Standard testing protocols were taken from the Malaria Research Unit, World Health Organization, as well as methods proposed by the National Health Laboratory Services. The collection of mosquitoes from the target area indicated that An. arabienis is a seasonal species with populations increasing during warmer conditions. The mating compatibility between the three tested strains of An. arabiensis, namely the Old Mamfene strain (laboratory strain), New Mamfene Strain (wild strain) and the Genetic Sexing Strain, proved favorable due to statistically non-significant insemination rates. However, the results indicated that the laboratory-reared colony displayed greater fecundity and mean numbers of larvae hatched than the wild colony. Within strains, overcrowding of larvae affected the size of the male adults, although reduced size did not affect mating within each strain, as insemination rates were not statistically affected (p>0.05). Dyes were tested to track mating between sterile males and wild females. However, dye transfer from male to female during copulation resulted in mating compatibility being negatively affected. Further investigations are thus needed to determine a better approach to tracking females that have copulated with released males. Although the results indicate that laboratory-reared males can compete successfully with their wild counterparts, field studies are required to verify these laboratory results.
Mosquitocidal activity against Anopheles arabiensis of plants used as mosquito repellents in South Africa.
(2014) Mavundza, Edison Johannes.; Van Staden, Johannes.; Finnie, Jeffrey Franklin.; Maharaj, Rajendra.
Ten plant species that are used as mosquito repellent in South Africa, Aloe ferox (leaves), Atalaya alata (leaves), Balanites maughamii (bark), Clausena anisata (leaves), Croton menyaarthii (leaves), Lippia javanica (leaves), Melia azedarach (leaves), Olax dissitiflora (bark), Sclerocarya birrea (seeds) and Trichilia emitica (seeds) were screened for adulticidal, larvicidal and repellent activities against Anopheles arabiensis, a potent malaria vector in South Africa. The plant extracts were screened following the WHO standard methods with slight modifications. The plant materials were extracted separately with ethanol (EtOH) and dichloromethane (DCM). All the extracts showed adulticidal activity. The highest activity was observed in the DCM extract of A. ferox leaves with an EC50 value of 4.92 mg/ml. With regards to larvicidal screening, all the DCM extracts showed larvicidal activity, while only five EtOH extracts showed activity. The highest larvicidal activity was found in the DCM extract of O. dissitiflora bark with an EC50 value of 25.24 μg/ml. All the investigated plants showed no repellent activity. Due to its good larvicidal activity, O. dissitiflora was evaluated for antibacterial, antifungal and antiplasmodial activities. The antibacterial activity was evaluated against two Gram-positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative (Escherichia coli and Klebsiella pneumoniae) bacteria using the micro-dilution assay. The micro-dilution assay was also used to evaluate the antifungal activity of O. dissitiflora against Candida albicans. The antiplasmodial activity was evaluated against a chloroquine-sensitive strain of Plasmodium falciparum (D10) using the parasite lactate dehydrogenase assay. Both DCM and EtOH extracts showed good antibacterial activity against all four tested strains with MIC values less than 1 mg/ml. They also showed good antifungal activity with MIC values less than 1 mg/ml. Both DCM and EtOH extracts showed a moderate antiplasmodial activity, with IC50 values of 15.6 and 45 μg/ml, respectively. Good larvicidal activity observed in the DCM extract of O. dissitiflora bark prompted an attempt to isolate active compounds. Two active compounds were isolated from O. dissitiflora bark, ximeninic acid and a mixture of two closely related compounds (exocarpic acid and octadec-9,11-diynoic acid). The mixture of exocarpic acid and octadec-9,11-diynoic acid exhibited the highest larvicidal activity with an EC50 value of 17.31 μg/ml compared to ximeninic acid which had an EC50 value of 62.17 μg/ml. The results of the present study showed that the bark of O. dissitiflora and leaves of A. ferox may have potential to be used as larvicides and adulticides against An. arabiensis mosquitoes, respectively. This study also indicated that the bark of O. dissitiflora may have potential to be used as an antibacterial, antifungal and antimalarial agent.