Vector-borne diseases: Integrated Vector Management (IVM)

This article was written by Dr Mojca Kristan, Research Fellow in Medical Entomology, London School of Hygiene & Tropical Medicine.

Introduction

Integrated Vector Management (IVM) was developed by the World Health Organization (WHO) as the new strategic approach to control vector borne diseases (VBDs) by optimising the use of resources and tools available for vector control to prevent vector-human contact in an efficient, cost-effective and sustainable manner. IVM approach depends on collaboration of the health sector, various public and private agencies, and communities, while focusing attention on capacity building at different levels in order to plan, implement, monitor and evaluate vector control operations (World Health Organization, 2012, Chanda et al., 2008, Chanda et al., 2017).

Furthermore, by using the IVM approach several diseases can be addressed at the same time, either because some vectors transmit several diseases or because some interventions are effective against several vectors (World Health Organization, 2012).

The main impact of IVM seen so far has been the reduction of vector breeding sites, improvement of the entomology index, and lowering of parasite rates. Other beneficial outcomes of IVM have been improved capacity, empowerment, inter-sectoral collaboration and community knowledge (Marcos-Marcos et al., 2018). Although a lot has been achieved in promotion and adoption of IVM, the actual adoption of the IVM concept into existing VBD control programs and implementation has been slow, with successful operational experience in deployment of the full five elements of IVM only documented from a few countries – including Eritrea, Kenya, and Zambia (Chanda et al., 2017).

Example 1: Zambia – successfully using IVM for malaria control

Malaria control in Zambia started in 1929 and the country was one of the early adopters of environmental management. Indoor residual spraying (IRS) with DDT (dichlorodiphenyltrichloroethane) started in the 1950s and mosquito net use started in the 1980s. However, with reductions in vector control and the development of resistance of Plasmodium malaria parasites to chloroquine, malaria incidence started rising in the 1970s, reaching 394 cases per thousand in 2002 (Chanda et al., 2013b).

In 2002, the Government of Zambia adopted a new National Malaria Treatment and Control Policy, with IVM adopted as a key strategic approach to vector control, and implementation was started in 2003 (Chanda et al., 2008). The main vector control interventions currently being used are IRS and insecticide treated nets (ITNs), while larviciding and environmental management are supplementary interventions. The use of vector control interventions is guided by eligibility criteria based on local evidence within the national guidelines, while the deployment of tools has been streamlined through a geographical information system (GIS)-based decision support system (DSS). GIS-based sentinel sites were established for the continual monitoring of key entomological and parasitological indicators (e.g. parasitaemia risk, insecticide resistance profiles in vectors), which has also improved the routine tracking of epidemiological impact of interventions (Chanda et al., 2012b).

Prior to the implementation of interventions, a number of feasibility assessments were conducted by districts to ensure that the use of interventions was based on knowledge of factors influencing local vector biology, disease transmission and morbidity, as the epidemiology of the disease varies on a small scale. This is something that is not always done, but systematic studies on vector bionomics and monitoring of insecticide resistance should be an essential component of IVM to facilitate evidence-based decisions on vector control, especially with the spread of insecticide resistance, potential changes in vector behaviour and potential shifts in vector species composition.

IRS has been is scaled up from 5 districts and 342,137 people in 2003, to 72 districts in 2012, now covering more than 5 million people. Pyrethroids, organophosphates, DDT and carbamates are used in an annual campaign carried out prior to the peak malaria transmission season. The use of DDT has been discontinued since 2010 due to development of insecticide resistance and in adherence to the Stockholm convention on Persistent Organic Pollutants (POPs). Spraying is done by Community Health workers (CHWs) and Neighbourhood Health Committees (NHCs) under the supervision of District Health Management Teams (DHMTs) in targeted districts. The quantification of commodities and equipment for IRS has been made more efficient with the help of GIS-based enumeration and geo-coding of structures to be sprayed (Chanda et al., 2012a, Chanda et al., 2013a, Chanda et al., 2008).

ITNs are implemented in rural areas only. The coverage has been increasing since 2000, with mass distributions taking place since 2005; long-lasting insecticide-treated nets (LLINs) have been distributed since 2007. The aim is to achieve universal (100%) coverage with at least 85% utilization rates in all eligible areas. Over nine million LLINs have been distributed country-wide. Household ITN ownership has increased from 44% in 2006 to 73% in 2010, while the use of nets by children under 5 years increased from 24% in 2006 to 50% in 2010 (Chanda et al., 2012a, Chanda et al., 2013a, Chanda et al., 2008).

Larval source management (LSM) has been a part of Zambian IVM strategy since 2005, beginning with the launch of environmental management (Chanda et al., 2008). It is implemented during dry seasons in collaboration with the local authorities and communities in urban and peri-urban areas, where vector breeding sites are discreet, few, fixed and findable. Studies to evaluate efficacy of different larvicides were carried out in 2007 (Chanda et al., 2007). Microbial larvicides Bacillus thuringensis israelensis (Bti) and Bacillus sphericus (Bs) have been used, while simple environmental modification and manipulation approaches such as canalisation, draining and land filling have been implemented in addition to larviciding. With limited funding and doubts surrounding LSM, its implementation remains minimal (Chanda et al., 2013a, Chanda et al., 2008).

Systematic monitoring and evaluation (surveillance) are critical to track progress and to evaluate outcomes and the impact of interventions (Chanda et al., 2013b). Primary entomological indicators such as vector species presence, densities, infectivity, resting and feeding behaviour, and insecticide resistance status, are being monitored, together with the quality of spraying. The major malaria vectors in Zambia are Anopheles gambiae.s.s, An. arabiensis and An. funestus. Monitoring and evaluation of control activities show that all three species have been successfully controlled – An. gambiae s.s appears to have been eliminated in IRS areas, while An. funestus and An. arabiensis populations have been supressed to minimal levels, and no infective vectors have been found in areas with IRS or ITNs, resulting in the reduction of malaria transmission and community wide protection. However, the discovery of DDT and pyrethroid resistance will present a challenge to the sustainability of the vector control programme (Chanda et al., 2011). Insecticide resistance management plan was developed in response and has been successfully implemented (Chanda et al., 2016).

Epidemiological monitoring is conducted through a routine surveillance reporting system and nationally representative cross-sectional population-based household surveys. Epidemiological data indicate marked reduction in malaria-related morbidity and mortality, a decrease in parasite prevalence among children under the age of five, and a decline in the percentage of children with severe anaemia. In addition, the number of malaria cases and deaths in 2008 was 55% and 60% lower, respectively, compared to the average in 2001 to 2002 (Chanda et al., 2013b). The importance of surveillance is discussed in more detail in other sections of this MOOC.

Many challenges remain in Zambia such as lack of utilization of ITNs and net misuse; lack of advocacy on supplementary interventions resulting in limitation in their funding; increased population; improvements needed in coordination at provincial and district levels; limited enforcement of statutory instruments; lack of total commitment by municipalities. Limited entomological capacity for surveillance to date has restricted the detection of potential temporal changes in vector bionomics throughout the country.

Overall the IVM programme in Zambia, however, has been a success and has made great progress in implementing WHO-recommended policies and strategies, taking into account the interventions that are appropriate in different epidemiological settings and are based on evidence. Following the successful application of IVM, which included increases in ITN and IRS coverage and establishment of environmental protection strategies, malaria-related deaths have been reduced by 66% (Chanda et al., 2017, Chanda et al., 2013b, Chanda et al., 2008). These achievements can be attributed to increased advocacy and provision of a suitable legal and regulatory policy framework; a newly developed malaria communication strategy between the Ministry of Health, public, private and civil sectors ; efficient partnership coordination including strong community engagement and participation due to employment of vector control and health workers from local communities; increased financial resources; and evidence-based deployment of key technical interventions in accordance with the national malaria control programme policy and strategic direction (Chanda et al., 2017, Chanda et al., 2013a).

Example 2: Two birds with one stone – malaria and filariasis control

A number of VBDs overlap in geographic distribution and some are transmitted by the same vectors. Furthermore, many currently used vector control interventions are effective against multiple VBDs. Therefore, combining vector control programmes to try to control several VBDs simultaneously would allow for shared use of certain control resources and efforts and might be more cost-effective, resulting in more sustainable disease reductions (Golding et al., 2015).

There are many similarities between malaria and lymphatic filariasis (LF) transmission: both diseases may be transmitted by the same or related Anopheles vector species; both are potentially controlled by the same vector-control interventions; humans are the main hosts; both are associated with poverty and poor environmental sanitation (van den Berg et al., 2013). The current Global Malaria Programme (GMP) and Global Programme for Elimination of Lymphatic Filariasis (GPELF) share the goals of local elimination and global eradication of the two diseases by achieving universal coverage of populations at risk with appropriate interventions (van den Berg et al., 2013).

GPELF was launched in 2000 with the principal objective of reducing the transmission of Wuchereria bancrofti and Brugia spp., the causative agent of LF, through the application of annual mass drug administration (MDA), aiming to eventually eliminate the disease. However, it has since been recognised that vector control activities will be required in addition to MDA if the program is to succeed, especially in Africa where many of the endemic countries have faced a number of challenges, including co-endemicity of LF and Loa loa, where MDA of ivermectin cannot be implemented due to serious adverse events (Bockarie et al., 2009, Kelly-Hope et al., 2013).

In places where malaria and LF are co-endemic and Anophelines have been implicated as principal vectors for both, the use of untreated and insecticide treated bed nets and IRS – originally for malaria control purposes – have significantly reduced filarial rates, in many cases more successfully than malaria (van den Berg et al., 2013).

In the Solomon Islands, indoor residual spraying with DDT for malaria control was successful in reducing transmission and eventually eliminating Anopheles-transmitted filariasis (Webber, 1977, Webber, 1979). In Papua New Guinea, both untreated nets in the absence of MDA and treated nets together with MDA had a strong effect on microfilariae (Burkot et al., 1990, Prybylski et al., 1994). On the Kenyan coast, the use of ITNs for malaria control resulted in significant suppression of W. bancrofti transmission (Bogh et al., 1998).

Mass distribution of LLINs for malaria control in sub-Saharan Africa, over the last decade, is thought to have also reduced the incidence and transmission of LF (Chanda et al., 2017, Golding et al., 2015, Stone et al., 2014). In northern Uganda, a substantial reduction in W. bancrofti infection prevalence in mosquitoes and infectivity in humans were detected where both MDA and LLINs were used, but the contribution of LLINs remains unclear (Ashton et al., 2011). LF is also endemic in Zambia, where a significant decline in LF prevalence was observed across the country between 2003 and 2014. While bed nets have been widely used in the country since early 2000s and MDA was only scaled up to reach the full coverage in 2015, the causal relationship between ITN coverage and LF prevalence is not clear (Nsakashalo-Senkwe et al., 2017).

Even where malaria and filariasis vectors are different (Anopheles and Culex, respectively), the use of environmental management for malaria and LF should be considered as part of IVM, including the construction of soakage pits, cleaning of drains, and improvement of sanitation (van den Berg et al., 2013). In Pondicherry, India, LF is transmitted by Culex mosquitoes in urban areas, while malaria is transmitted by Anopheles mosquitoes and concentrated in rural areas. Environmental management was implemented at large scale with the participation of communities and inter-sectoral collaboration. Despite these two diseases having separate vectors, the microfilariae burden dropped substantially for young children, while malaria was locally eliminated (Rajagopalan et al., 1988, Rajagopalan et al., 1987).

Integrated vector management for control of malaria and LF would most likely result in more efficient use of resources across all activities. Integration of programmes would also improve evaluation and allow for more accurate attribution of the observed effects to the resources used. Finally, integration would ultimately result in improved control of both diseases (van den Berg et al., 2013).

Conclusions

There is clear evidence of the potential IVM has to enable greater overall control of VBDs in the face of challenges such as the spread of insecticide resistance, climate change, and availability of limited resources. This has been demonstrated by the Zambian experience of using a coordinated multifaceted approach to control malaria, and by the use of established vector control interventions to control multiple diseases, such as malaria and LF, at the same time.