Introduction 

Vector control measures are vital techniques used in public health to reduce the incidence of Vector-borne diseases (VBDs), which occur when a disease is spread through vectors like mosquitoes, ticks, and fleas. Not all parasitic diseases are vector-borne, but many are, such as malaria, dengue fever, and leishmaniasis. These parasitic diseases create significant global health challenges, especially in tropical and subtropical regions. The World Health Organisation (WHO) estimates that VBDs account for a considerable infectious disease burden, causing millions of deaths each year.¹ 

Vector control is essential for many reasons; it protects vulnerable populations, prevents outbreaks and reduces healthcare costs. By employing various techniques, for example, environmental management, insecticide-treated nets, and public education, communities can significantly reduce disease-carrying vectors and mitigate the spread of parasitic infections. This article will explore the variety of vector control measures that are currently in use and their crucial role in combating the incidence of parasitic disease worldwide.

Understanding parasitic diseases and their vectors 

A vector is an organism that transmits a pathogen (a virus, bacteria or a parasite) from one host to another, resulting in the spread of a disease, namely a ‘Vector-Borne Disease’. Examples of vectors include: 

• Mosquitoes are vectors for malaria, dengue fever, Zika virus, and West Nile virus
• Ticks can transmit Lyme disease and Rocky Mountain spotted fever
• Sandflies are vectors for leishmaniasis, sandfly fever and Rift Valley fever

This article is focused on the spread of parasitic vector-borne diseases. A parasite is defined as an organism that either lives on a host or obtains nutrients from or at the expense of a host.² It is important to note that parasitic infections also affect pets and wild animals, which have a great environmental and economic impact.³ Not all parasitic diseases are vector-borne; they can also be transmitted through:

• Blood: Sharing used needles or syringes, as well as blood transfusions (Donated blood should always be checked through screening protocols)
• Direct contact: Skin-to-skin contact with a person or animal with the parasite
• Food and water: Eating undercooked meat, parasites can live in swimming pools or natural water sources such as lakes and rivers
• Congenitally: Transmission from mother to baby during pregnancy, birth, or when breastfeeding
• Faeco-orally: When parasites are ingested through food or surfaces that have been contaminated

Overview of vector control measures 

Vector control measures are vital techniques that manage the vectors, i.e the organisms that transmit vector-borne diseases (VBDs).⁴ The key control strategies involve:

1. Environmental Management: This eliminates mosquito breeding sites by draining stagnant water or filling in ditches that would otherwise collect rainwater. Another effective technique is managing water storage practices by using tightly sealed containers and cleaning them regularly
2. Biological Control: Using natural predators, for example, fish that eat mosquito larvae (e.g., Gambusia affinis) to control transmission levels. Certain bacteria can also target vector populations, such as Wolbachia bacteria, which target mosquitoes
3. Chemical Control: insecticides used for indoor residual spraying (IRS), which involves spraying indoor walls and surfaces. Chemical control also utilises larvicides in water bodies, along with insecticide-treated nets (ITNs) for personal protection⁵
4. Personal Protection: Encouragement of the use of repellents on the skin that include DEET (N, N-Diethyl-meta-toluamide), the most commonly used repellent for biting insects.⁶ It works by masking human scent, which would otherwise attract insects to human skin. Personal protection also encourages the use of long clothing to minimise exposure to vectors
5. Integrated Vector Management (IVM): This is a comprehensive multi-strategy approach tailored to local needs based on local epidemiological data (epidemiology refers to the branch of medicine that deals with how much a disease occurs in a certain area or population and why). IVM emphasises involving the local community, sustainability, monitoring and optimising resource use⁷

Evidence of effectiveness and case studies

Roll back malaria (RBM)

• This initiative started in 1998 by joint efforts from the World Health Organisation (WHO), the United Nations Children’s Fund (UNICEF), the United Nations Development Programme (UNDP), and the World Bank
• The initiative aims to reduce malaria morbidity and mortality through integrated vector management (IVM) and early diagnosis. Between 2000 and 2015, malaria mortality rates went down by 60% worldwide⁸
• The introduction of insecticide-treated nets, indoor residual spraying (IRS), and rapid diagnostic tests was a vital vector control measure of the initiative

Schistosomiasis control efforts

• Like malaria, Schistosomiasis is another parasitic infection caused by trematode worms.⁹ These worms require freshwater snails to develop from larvae into adult worms. Infection occurs when people enter bodies of water where the snails live, making it a waterborne parasitic infection 
• Snail control measures have included the use of environmental management and molluscicides (snails are a type of mollusc, which are invertebrates with a soft body, often protected by a shell) 
• A systematic review showed that these targeted snail control measures can lead to a significant reduction in schistosomiasis.¹⁰ Other techniques used include the use of mass drug administration (MDA).11 MDA is a mass treatment strategy given to populations at risk regardless of whether they have an infection or not, to achieve the eventual elimination of the infection

Challenges in vector control

Resistance to Insecticides: Resistance to insecticides is a major challenge to vector control. Similar to antibiotic resistance, vectors like mosquitoes and ticks develop resistance to chemicals used in insecticides. This creates a need for continuously developing new insecticides and implementing rotation strategies, both of which create financial and resource burdens.

Environmental Impact: The use of chemical insecticides is a cause for concern to the environment and the natural balance of ecosystems. Due to food chains, even non-target species can be affected, and beneficial insects can be reduced in numbers, disrupting local ecological systems. 

Socioeconomic Factors: Socioeconomic conditions play a primary role in the implementation of vector control strategies. In less developed countries with limited resources, funding, infrastructure, and low levels of health education can undermine effective programs. 

Climate Change: Climate change can change the habitats that vectors exist in and can widen the geographical range of many disease-carrying species. Rising temperatures and changing patterns of precipitation can improve breeding conditions for vectors, which results in an increase in disease transmission and outbreaks in regions that were previously unaffected.

Conclusion 

Vector control is a crucial public health strategy for reducing the incidence of vector-borne parasitic diseases. The challenges of insecticide resistance, impact on the environment, socioeconomic factors, and climate change mean that innovative solutions and collaborative efforts are required to tackle these parasitic diseases. Continued funding in research, engagement of communities, and global partnerships such as the ‘Roll Back Malaria’ initiative are critical to creating ongoing, sustainable vector control strategies. By addressing these challenges through global partnerships, public health outcomes can be achieved, and we can mitigate the burden of vector-borne diseases worldwide. 

Frequently asked questions (FAQs)

What is a vector?

A vector is an organism that spreads pathogens, such as viruses, bacteria or parasites, from one host to another, resulting in the spread of diseases. Examples include mosquitoes, ticks and fleas. 

What are the most common vector-borne parasitic diseases?

Malaria, schistosomiasis, and leishmaniasis are common vector-borne parasitic diseases.

What strategies are being implemented to combat vector resistance to insecticides?

Strategies include insecticide rotations, developing new insecticide chemicals, and utilising integrated vector management (IVM).