South Africa aims to eliminate malaria within its borders by 2018. Despite well-coordinated provincial vector control programmes that are based on indoor residual insecticide spraying, low-level residual malaria transmission continues in the low-altitude border regions of the north-eastern sector of the country. In order to identify the underlying causes of residual transmission, an enhanced vector surveillance system has been implemented at selected sites in the Mpumalanga and KwaZulu-Natal (KZN) provinces. The collection periods for the data presented are March 2015 to April 2016 for Mpumalanga and January 2014 to December 2015 for KZN. The mosquito collection methods used included indoor and outdoor traps based on the use of traditional ceramic pots, modified plastic buckets and exit window traps (KZN only). All Anopheles funestus species group mosquitoes collected were identified to species and all females were screened for the presence of Plasmodium falciparum sporozoites. Two An. vaneedeni females, one from each surveillance site, tested positive for P. falciparum sporozoites. These are the first records of natural populations of An. vaneedeni being infective with P. falciparum. As both specimens were collected from outdoor-placed ceramic pots, these data show that An. vaneedeni likely contributes to residual malaria transmission in South Africa.

ProblemTraditional random sampling at community level requires a list of every individual household that can be randomly selected in the study community. The longitudinal demographic surveillance systems often used as sampling frames are difficult to create in many resource-poor settings.ApproachWe used Google Earth imagery and geographical analysis software to develop a sampling frame. Every household structure within the catchment area was digitized and assigned coordinates. A random sample was then generated from the list of households.Local settingThe sampling took place in Lilongwe, Malawi and formed a part of an investigation of the intensity of Plasmodium falciparum transmission in a multi-site Phase III trial of a candidate malaria vaccine.Relevant changesCreation of a complete list of household coordinates within the catchment area allowed us to generate a random sample representative of the population. Once the coordinates of the households in that sample had been entered into the hand-held receivers of a global positioning system device, the households could be accurately identified on the ground and approached.Lessons learntIn the development of a geographical sampling frame, the use of Google Earth satellite imagery and geographical software appeared to be an efficient alternative to the use of a demographic surveillance system. The use of a complete list of household coordinates reduced the time needed to locate households in the random sample. Our approach to generate a sampling frame is accurate, has utility beyond morbidity studies and appears to be a cost-effective option in resource-poor settings.

Anopheles arabiensis (Patton; Diptera: Culicidae) is a major malaria vector in the southern African region. In South Africa, effective control of this species using indoor-based interventions is reduced owing to its tendency to rest outdoors. As South Africa moves towards malaria elimination there is a need for complementary vector control strategies. One of the methods under consideration is the use of the sterile insect technique (SIT). Key to the successful implementation of an SIT programme is prior knowledge of the size and spatial distribution of the target population. Understanding mosquito population dynamics for both males and females is critical for efficient programme implementation. It is thus necessary to use outdoor-based population monitoring tools capable of sampling both sexes of the target population. In this project mosquito surveillance and evaluation of tools capable of collecting both genders were carried out at Mamfene in northern KwaZulu-Natal Province, South Africa, during the period January 2014 to December 2015. Outdoor- and indoor-resting Anopheles mosquitoes were sampled in three sections of Mamfene over the 2-yr sampling period using modified plastic buckets, clay pots and window exit traps. Morphological and molecular techniques were used for species identifications of all samples. Wild-caught adult females were tested for Plasmodium falciparum (Welch; Haemosporida: Plasmodiidae) infectivity. Out of 1,705 mosquitoes collected, 1,259 (73.8%) and 255 (15%) were identified as members of either the Anopheles gambiae complex or Anopheles funestus group respectively. An. arabiensis was the most abundant species contributing 78.8% of identified specimens. Mosquito density was highest in summer and lowest during winter. Clay pots yielded 16.3 mosquitoes per trap compared to 10.5 for modified plastic buckets over the 2-yr sampling period. P. falciparum infection rates for An. arabiensis were 0.7% and 0.5% for 2014 and 2015, respectively. Logistic regression analysis showed an association between An. arabiensis catches with Section and season of collection but not with sex and collection methods. These data confirmed the presence of a perennial An. arabiensis population at Mamfene and constitute the first records of P. falciparum infective An. arabiensis from South Africa, confirming this species as a major vector in the malaria endemic provinces of the country.

BackgroundAnopheles arabiensis Patton is primarily responsible for malaria transmission in South Africa after successful suppression of other major vector species using indoor spraying of residual insecticides. Control of An. arabiensis using current insecticide based approaches is proving difficult owing to the development of insecticide resistance, and variable feeding and resting behaviours. The use of the sterile insect technique as an area-wide integrated pest management system to supplement the control of An. arabiensis was proposed for South Africa and is currently under investigation. The success of this technique is dependent on the ability of laboratory-reared sterile males to compete with wild males for mates. As part of the research and development of the SIT technique for use against An. arabiensis in South Africa, radio-sensitivity and mating competitiveness of a local An. arabiensis sexing strain were assessed.MethodsThe optimal irradiation dose inducing male sterility without compromising mating vigour was tested using Cobalt 60 irradiation doses ranging from 70-100 Gy. Relative mating competitiveness of sterile laboratory-reared males (GAMA strain) compared to fertile wild-type males (AMAL strain) for virgin wild-type females (AMAL) was investigated under laboratory and semi-field conditions using large outdoor cages. Three different sterile male to fertile male to wild-type female ratios were evaluated [1:1:1, 5:1:1 and 10:1:1 (sterile males: fertile, wild-type males: fertile, wild-type females)].ResultsIrradiation at the doses tested did not affect adult emergence but had a moderate effect on adult survivorship and mating vigour. A dose of 75 Gy was selected for the competitiveness assays. Mating competitiveness experiments showed that irradiated GAMA male mosquitoes are a third as competitive as their fertile AMAL counterparts under semi-field conditions. However, they were not as competitive under laboratory conditions. An inundative ratio of 10:1 induced the highest sterility in the representative wild-type population, with potential to effectively suppress reproduction.ConclusionLaboratory-reared and sterilised GAMA male An. arabiensis at a release ratio of 3:1 (3 sterile males to 1 wild, fertile male) can successfully compete for insemination of wild-type females. These results will be used to inform subsequent small-scale pilot field releases in South Africa.