Malaria Vectors and Vector Control

Malaria Transmission in Southern Africa

Mosquitoes of the genus Anopheles transmit the four Plasmodium species, P. falciparum, P. vivax, P. ovale and P. malariae that cause human malaria. There are about 400 species of Anopheles mosquitoes. But only about 70 of these are indicated in human malaria transmission at different levels in different areas. Some are important vectors while others play a secondary role.

Mainly three species, Anopheles arabiensis, An. gambiae and An. funestus transmit malaria in Southern Africa. While An. merus plays a secondary role in some countries. Anopheles arabiensis is the predominant vector particularly in the epidemic prone countries (Botswana, Namibia, South Africa, Swaziland and Zimbabwe). In places where malaria is more stable (in Angola, Malawi, Mozambique, Tanzania, and Zambia) An. gambiae is the main vector. Anopheles funestus also plays an important role in these areas of high malaria endemicity.

	Biology of the malaria vectors in Southern Africa
	Selective vector control and personal protection methods
	Current priorities in vector control programs in Southern Africa
	Vector Control in Malaria Chart

	DDT - The Facts
	Insecticide Treated Mosquito Nets - The Malaria Condom
	Redes Mosquiterias Tratadas com Insecticida (RMTIs) Um Metodo de Prevencao Contra MALARIA
	Indoor Residual House Spraying in Southern Africa
	Monitoring and Evaluation of Quality and Effectiveness of IRHS
	More Publications

Reference Documents

	WHO Position on DDT Use in Disease Vector Control Under the Stockholm Convention on Persistent Organic Pollutants
	Frequently Asked Questions on DDT Use for Disease Vector Control
	Things You Need to Know About DDT Use Under The Stockholm Convention
	Space Spray Application of Insecticides for Vector and Public Health Pest Control - A Practitioner's Guide
	ITN Interventions - A Manual for Programme Managers
	Malaria Entomology and Vector Control - A Learner's Guide
	Guidelines on the Use of ITNs in Africa
	Instructions for Treatment and Use of ITNs
	Safe and Effective Use of Household Insecticide Products
	Manual for Indoor Residual House Spraying
	Supplies for Monitoring Insecticide Resistance in Disease Vectors

Biology of the Malaria Vectors in Southern Africa

Breeding behavior

Both A. arabiensis and An. gambiae breed mostly in small water collections of stagnant and muddy seepage and rainwater with partial or full sunlight. The species avoid polluted water. Vegetation can be absent or present. Anopheles funestus prefers large bodies of fresh water marshes with full or partial sunlight. Larvae occur among floating or emerging vegetation. A summary on the preferred breeding sites of the three species is presented in Table 1.

Feeding and resting behaviors

The three species bite indoors and outdoors similarly as long as hosts are available (Table 2). Anopheles gambiae and An. funestus are relatively more anthropophilic (preferring biting humans to animals) and endophilic (rests mostly indoors) than An. arabiensis. An. funestus rarely rests outdoors.

Vectorial efficiency

Malaria sprozoite rates are generally higher in populations of An. gambiae, followed by An. funestus, than in An. arabienesis (Table 2). There is also a consensus the latter species has a shorter survival rate than An. gambiae although this needs more laboratory and fieled studies.

These biological variations indicate that An. gambiae and An. funestus are more effective vectors with a capacity to sustain malaria transmission at lower vector population densities than An. arabiensis.

The fact that An. gambiae and An. funestus are endophilic means that properly applied residual house spraying can significantly reduce malaria transmission in areas where the vectors are important. In fact, An. funestus is no longer an important vector after its suppression by residual house spraying in areas of the sub-region where the method is a major component of malaria control programs. The partial exophilic behavior of An. arabiensis

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Table 1. Summary of breeding behavior of An. gambiae s.s, An. arabiensis and An. funestus and possible larval control methods

Species Larval control method

+++ Breeds most +++ Most suitable

++ Breeds often ++ More suitable

+ Breeds some times + Suitable

--- Rarely ( if at all ) -- Not suitable

NA Not applicable

might affect the effectiveness of residual house spraying in areas where the species is an important vector. However, the low vectorial efficiency of the species means it requires a high population density to sustain malaria transmission at a significant level. This implies that vector control interventions that reduce the population density of An. arabiensis by at least 50% can significantly reduce malaria transmission.

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Table 2. Biological information related to vectorial efficiency of the three important malaria vectors in Southern Africa

* Occupied by humans and animals

+ Proportion of female mosquitoes found fed on human blood = percentage Human Blood Index (HBI)

++ Proportion of female mosquitoes found containing malaria sporozoites in their salivary glands = percentage sporozoite rate

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Selective Vector Control and Personal Protection Methods

1. Any intervention targeted to reducing vector population density and survival that aims as an end product to reduce malaria transmission is described as vector control. Selective vector control is the application of site and time specific control methods that are cost-effective when applied in a particular environment and time.

2. Personal protection methods mainly protect the individuals who use them from malaria infection by reducing human-vector contact without necessarily reducing vector density or over all malaria transmission.

In Southern Africa both selective vector control and personal protection methods are widely used at different levels in different countries. The current implementation status and population coverage of vector control in Southern Africa are compiled in Tables 3 and 4, respectively. However, most figures in Table 4 are estimated and extrapolated from the existing limited information (data) at the sub-regional level.

Table 3. Vector control and personal protection and their management in Southern Africa as of 2000

^a Limited in urban areas ^? Further confirmation required

^b Individual use - Information not available

RHS-Residual House Spraying bednets - Both treated and non-treated

ITNSC- ITN subcommittee CSC-Vector control Subcommittee

⁺⁺⁺ Significat applied

⁺⁺ Moderately applied

⁺ Limited application

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Current Priorities in Vector Control Programs in Southern Africa

In order to improve vector control interventions and increase their effectiveness in Southern Africa the following are the priorities.

• Strengthening supervision and monitoring capacity of NMCPs for RHS and other vector control methods at national and district levels
• Establishing and strengthening documentation, reviewing and reporting systems
• Expanding the use of ITNs
• Strengthening vector surveillance capacity at national level to ensure implementation of evidence based vector control interventions
• Establishing sentinel sites (for monitoring and evaluation) and Vector Control Sub-committees

Table 4. Estimated size of population living in malarious areas and proportion of the population targeted to be protected by Residual House Spraying (RHS) and own Mosquito Nets (MN)(insecticide treated and non-treated) in Southern Africa as of 1999.

-- Information not available

NA - Not applicable

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