Few may know that today – August 20 – marks the relatively obscure observance of World Mosquito Day, but mosquitoes (Spanish for “little flies”) are far from obscure. These insects have coexisted with humans for thousands of years in varying numbers depending on the effectiveness of vector control efforts, and have likely caused more suffering than any other living organism in the history of humankind. According to the World Health Organization (WHO), they are responsible for the death of more than a million people every year.
Several mosquito species – there are about 3,500 in total – are vectors for parasitic and arboviral diseases. Among these, malaria and lymphatic filariasis (LF) are the two mosquito-borne diseases that contribute to the largest global burden of mortality and morbidity. They are also two of the most prevalent mosquito-borne diseases in Papua New Guinea (PNG). With 24 percent of all malaria cases and 49 percent of malaria deaths in the Asia-Pacific in 2019, the country bears the highest malaria burden in the region. LF, commonly known as elephantiasis, remains a neglected tropical disease, and is prevalent in 62 out of PNG’s 89 districts, with prevalence rates ranging up to 70 percent.
There is a great geographical variety in the burden of malaria and LF in PNG. For example, there is very little malaria in the highlands, where 40 percent of the population resides, as the region’s typically lower temperatures affect vector distribution and prevent ongoing transmission. Climate change, however, is rapidly changing the behavior of mosquitos. The central highlands, once malaria-free, are now experiencing an alarming increase in malaria transmission. In contrast, LF is more concentrated, with a higher prevalence in the lowland and coastal districts.
Positively, there has been strong political commitment to eliminate both malaria and LF in PNG. Former Prime Minister Peter O’Neill committed to malaria elimination at the London Malaria Summit in 2018 and endorsed the Asia Pacific Leaders Malaria Elimination Roadmap. The Government of PNG is also strengthening efforts towards elimination of LF. PNG is a part of a regional collaborative effort comprising the health ministries of 22 islands and territories in the Pacific region, referred to as “PacELF,” which are committed to taking action against LF.
While there is political commitment at the highest level, there are gaps in implementation of programs at subnational levels. Local-level governments are often not resourced adequately to deliver provincial and lower-level healthcare services. There are also several healthcare issues which are competing for attention in a highly resource constrained environment. In addition, COVID-19 has further shrunk the resources available for implementing infectious disease programs.
This presents an opportunity to target cross-disease elimination by developing more cost-effective and integrated models of service delivery that can optimize available resources via evidence-based decision-making. The WHO also recommends exploring the added value of joint vector control interventions by harmonizing vector control plans to address the two diseases, and by sharing vector-control resources where appropriate.
Past studies have shown the inadvertent benefits of malaria vector control on LF, a notable example being from the Solomon Islands, where the malaria eradication initiative with indoor residual spraying resulted in the disappearance of LF entirely. PNG is well positioned to adopt an integrated approach to fighting malaria and LF, as both diseases are transmitted via the same vector. There is also an overlap in terms of geographical distribution. For example, PNG’s Milne Bay province is highly endemic for both malaria and LF. In fact, there is some historical evidence to suggest that vector control interventions conducted for malaria control in some parts of the country interrupted transmission of the parasitic worm that causes LF.
Another key issue is the use of long-lasting insecticidal nets (LLINs), which have resulted in behavioral changes to mosquito biting habits. In addition to a shift to outdoor biting from indoor biting, peak biting hours have also moved to early evening, when people are not protected by LLINs. Currently, LLINs are the only vector control tool being programmatically implemented in PNG.
It is a commonly accepted fact that a single vector control intervention is unlikely to result in disease elimination, particularly in countries with stable perennial transmission like PNG. There is therefore an urgent need to identify new vector control tools (VCTs) that can efficiently reduce human vector contact and protect people against vector-borne diseases. To support this, the Australian Department for Foreign Affairs and Trade and the Innovative Vector Control Consortium is supporting a project in PNG known as NATNAT, implemented through local partner organizations, to develop and adopt a framework for the assessment and adoption of new VCTs.
The heterogeneity in species of the vector for both malaria and LF in PNG adds to the complexity of vector control efforts. Routine entomological surveillance is key to ensuring that vector control approaches are locally tailored to prevent transmission. PNG doesn’t have a national surveillance plan and the capacity of the malaria program staff to undertake vector surveillance is limited. A review of the malaria program reveals that the program’s network of microscopy, its entomology capacity, and its training facilities are all severely under-resourced.
Another key area of focus is therefore to build the capacity of in-country entomologists and equip them with the necessary skills for effective vector surveillance and control of all vector-borne diseases. This lack of entomological capacity is not unique to PNG. As in many other parts of the world, the Asia-Pacific region faces a dearth of entomologists and vector control specialists to guide vector control interventions. While there are several important initiatives being undertaken to train entomologists in PNG and the region broadly, the needs are huge.
A more integrated response towards the control of vector-borne diseases, the introduction of new vector control tools, and the strengthening of entomological capacities will help accelerate progress towards the elimination of these ancient diseases of poverty. Piloting and adopting integrated approaches for cross-disease elimination will offer critical lessons for a more collaborative and coordinated approach in the region and beyond. Let us not miss the opportunities for greater efficiency, the strengthening of health systems, and improved impact. Elimination is possible, desirable, and economically and socially beneficial. Let us pursue it with renewed vigor in order to alleviate preventable suffering.