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Malaria Vectors and Vector Surveillance in Limpopo Province (South Africa)

Panelists

Chairperson: Dr Jesne Kistan

Presenter: Dr Lutho Magayiyana

Discussant: Dr Janine Martins

Expert: Dr Magen Riddin

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TABLE OF CONTENT

Introduction
Materials and Methods
Results
Discussions
Conclusions

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INTRODUCTION

South Africa has three malaria endemic provinces with sustained annual local transmission—Limpopo, Mpumalanga and KwaZulu-Natal. Limpopo Province, which borders Zimbabwe to the north and Mozambique to the east, has the highest malaria incidence. Other Provinces, such as Northwest and Gauteng, experience significant levels of imported malaria cases but no local transmission.

Anopheles gambiae and Anopheles funestus were the main vectors of malaria in South Africa, but the concerted indoor control efforts resulted in local extinction of both species. Since then it has been widely believed that Anopheles arabiensis is the primary remaining vector responsible for malaria transmission in South Africa.

The malaria vector control programmes occur in the three endemic Provinces undertake annual application of indoor residual spraying (IRS) using a mosaic approach comprising two different classes of insecticides, pyrethroids and organochlorines. They also conduct vector surveillance which for decades has been limited largely to the An. gambiae complex, mainly by way of larval collections.

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MATERIALS AND METHODS

Conducted a literature search using Google Scholar and PubMed.

Vector surveillance and methods used for new data presented here was targeted at known high-incidence and recurring malaria “hotspots” in the eastern Limpopo River valley region of Vhembe District. Collections were made in October and December 2017 and again in February, April and October 2018. Adult mosquitoes were collected using CO2-baited light traps and tent traps baited with dry ice CO2, cows and sometimes goats, and occasionally human landing catches.

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RESULTS

The first records reflecting Anopheles species composition and some idea of distribution and general abundance are those of Ingram and De Meillon, published in 1927 and 1929. They recorded a total of 16 anopheline species with An. Funestus and An. Gambiae included.
Swellengrebel et al. 1931- The results confirmed the distribution of the two vector groups, with An. funestus being restricted to the foothills along the mountain range and members of the An. gambiae complex more prevalent in the lowland areas. Later studies provided evidence for the restricted distribution of An. funestus being due to its preferred larval habitat of small streams or rivers in the area.
Steyn et al. 1955- This is the only historical survey recording the presence of An. listeri, collected to the east of Musina close to where the current survey was conducted.
La Grange and Coetzee 1987-1989-is especially useful as it reports on a detailed list of anopheline species collected using four different methods over a 27-month period in the village of Thomo, Limpopo Province. Direct comparisons of anopheline species composition and relative abundance can therefore be made with the October 2017–October 2018 survey conducted in Vhembe District.
Govere et al. 2000
Munhenga et al. 2014
Cornel et al 2018- Eight species of Anopheles comprising 63.1% of the total catch of 168 mosquitoes at Shingwedzi. No An. arabiensis was recorded from the sites.

Historical Surveys in Limpopo Province

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RESULTS

Historical Surveys in Limpopo Province

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Historical Surveys in Limpopo Province cont..

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For comparative purposes, it is useful to have a sense of Anopheles community composition in the neighboring malaria regions of Mpumalanga Province to the south, Zimbabwe to the north, and Mozambique to the east.

In Mpumalanga Province, Govere et al. conducted monthly collections of mosquitoes at 7 sites in the Lowveld Region between August 1997 and May 1998. A total of 5084 Anopheles were collected of which An. coustani was by far the most abundant 55.8%, followed by the An. funestus group 27.9% and the An. gambiae complex 8.6%.

North of Vhembe District, Sande et al. conducted anopheline surveys in the Mutare and Mutasa Districts of Manicaland Province, Zimbabwe, during the period November 2013 to April 2014.An. arabiensis was present only in very low numbers over the entire period, with An. funestus being relatively more abundant but in terms of overall numbers also very low, especially in comparison with An. Pretoriensis.

In neighboring southern Mozambique, Casimiro et al. and Kyalo et al. report on the presence of An. gambiae s.s. while An. funestus has been recorded by Brooke et al. and Casimiro et al.

Surveys in Surrounding Areas

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2017/2018 Vector Surveys

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DISCUSSIONS

Vector status of members of the anopheles Gambiae complex and their role in the Limpopo River Valley. In KwaZulu-Natal Province, An. arabiensis is common and has recently been implicated in malaria transmission, but various studies suggest that it is a rare species further north, especially in Limpopo Province, including the findings during the 2017–2018 survey of the Limpopo River Valley. Two other members of the An. gambiae complex occur widely in the warm, lowland regions of north-eastern South Africa where malaria remains endemic. The survey in the Limpopo River Valley showed that An. Quadriannulatus is common in inhabited rural areas but An. arabiensis is rare (aside from Pafuri and Malahlapanga in the wildlife conservation area of the Kruger National Park with few people at these sites). It is difficult to reconcile the generally accepted non-vector status of An. quadriannulatus and the scarcity of An. arabiensis with the rather high seasonal transmission of malaria that occurs in this northern region of South Africa, which suggests other vectors play a more important role.

Vector status of members of the Anopheles Funestus group and their role in the Limpopo River Valley. Anopheles funestus was historically a major vector of malaria in South Africa and continues to play a major role in malaria transmission in neighboring Mozambique and Zimbabwe. The surveys in 2017–2018, which yielded a solitary An. funestus female at Popallin Ranch close to the Zimbabwe border, suggests that any let-up in the annual indoor spraying programe may also create an opportunity for this species, as well as An. gambiae to re-enter and establish a foothold in Limpopo.

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DISCUSSIONS

Other anophelines of potential vector becomes important to consider the possible contribution of other mosquito species which could account for persistent low-incidence transmission, especially by species that feed outdoors and use cattle and other animals as additional blood-meal sources. Such “secondary” vectors may in fact then become the new “primary” vectors, and many such species have been incriminated in Africa.

A proportion of local malaria cases in Limpopo Province are likely to have been caused by the importation of infective mosquitoes into South Africa from neighboring highly endemic regions, especially Mozambique. This phenomenon is known as odyssean/suitcase malaria and is a likely contributor to malaria epidemiology in all of South Africa’s malaria affected provinces.

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CONCLUSION

Given that the available evidence suggests An. arabiensis almost certainly not playing a significant role in malaria transmission in the Vhembe District.

Vector surveillance is a complex process which requires surveillance over a prolonged period of time to identify species related to malaria transmission so that appropriate control measures can be targeted at such species.

From a public health perspective, prevention targeted at humans to stop transmission is equally important as vector targeted prevention strategies.

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