Misuse of nets a high risk

ENVIRONMENT

By GELINDE NAREKINE
MALARIA Malaria is an ancient disease that could be traced back to the very earliest human history. Hence, in the fourth century BC, it was accepted as a disease by Hippocrates – a Greek physician and philosopher, who is referred to as the ‘Father of Modern Medicine’.
In 1885, plasmodium was described as the parasite responsible for occurrence of malaria. By 1897, the whole transmission cycle of the parasite was fully described, followed with the demonstration in 1898 that malaria was transmitted by the female Anopheles mosquito.
Into the 21st century, malaria still remains a global overburdening health problem, thus, accounting for much of the disease burden of tropical counties. It causes over a million deaths a year, with an estimated 300-500 million episodes of acute illness annually in over 100 countries, where approximately 40 percent of the world’s population live.
Eradication efforts have been more or less, a nightmare for the scientific community and public health specialist for decades, or even, centuries. Its causative parasite is one of those hard-to-target pathogens, making vaccine discovery still a daunting task for the global scientific community.
Over many decades, various methods have been developed with mounting efforts to control and prevent transmission of malaria. An important innovation during the past two decades is the widespread introduction of nets impregnated with insecticides. These treated nets effectively reduce infection and death in many epidemiological settings.
When used by the majority of the community, they are intended to benefit not only individuals using them, but also those who sleep without treated nets, as they may receive fewer mosquito bites. Insecticide-treated nets have been highly e?ective for the control of malaria, with millions of lives saved since their development in the 1990s and wide distribution in the 2000s.
Pyrethroids
All treated nets contain pyrethroids, the only group of insecticides recommended by the World Health Organisation (WHO) for use on mosquito nets. Technically speaking, before insecticides are recommended by WHO, they undergo extensive laboratory testing to check if their use can cause acute and chronic toxicity.
These tests help scientists judge how these chemicals might affect humans, domestic animals, and wildlife in the case of exposure. Based on the results of such laboratory tests, pyrethroids are generally considered safe at low doses, and therefore, widely used in public health.
Pyrethroid insecticides have been extensively used in farms for control of pests that destroy plant crops. They are also used in forestry and veterinary practices, and even in urban environments for killing insects. In recent years, due to mosquitoes (and other insects) developing resistance, another chemical called piperonyl butoxide has been added to make more powerful formulations of pyrethroids. Claims are such that these insecticides do not pose any signi?cant health risk when they are used in mosquito nets and indoor house spraying.
At the global level, the safety of pyrethroid insecticides at low concentrations used to impregnate mosquito nets has been repeatedly expressed. Even leading mosquito net manufacturers insist that their products are not dangerous. And yet, many nets are labeled: “Do not wash in a lake or a river.” Some labels go even further, warning people to pour any water used in washing a net into a hole in the ground, “away from home, animals and wells.”
Warning labels such as this indicate that manufacturers and distributers do know that these chemicals are poisonous when subjected to natural environmental and biological conditions. Nevertheless, pyrethroid-treated mosquito nets are produced and widely distributed, especially to developing countries in massive quantities. More than two billion such nets have passed out since they were first introduced. The inevitable reality of this exercise is that, it is also a billion-dollar industry.
In spite of numerous positive publicity on their safety, scientific evidence shows that pyrethroid insecticides are highly toxic out in the natural environment than laboratory toxicity assays predict. They are poisonous for freshwater and marine lives, and even at the lowest concentrations can lead to dramatic reductions in a number of animal species. With the addition of other chemicals to pyrethroid formulations, the killing effects of the active ingredient is further enhanced. Such as this is an added danger for exposed freshwater ecosystems and their inhabiting organisms.
Although dismissed by scientists and malaria control personnel for years, there is increasing evidence con?rming use of insecticide-treated nets as ?shing nets in many parts of the developing world. A recent review of literature and a global survey of stakeholders in ?sheries, public health, conservation, and development sectors found that mosquito net ?shing is widespread worldwide. Numerous case studies have also been published, documenting frequent use of treated nets for ?shing.
Use of ttreated nets in PNG
Insecticide-treated nets were introduced to Papua New Guinea in 2004. This exercise has not only been beneficial in terms of reduction in malaria cases, but also come with unforeseen negative impacts. It has been observed that over time, users have been washing treated nets in rivers and streams or using them as fishing nets. Such practices introduce pyrethroids directly into freshwater systems. Given their high degree of toxicity, pyrethroids cause serious negative effects on the exposed invertebrates and fish.
In other developing countries, serious hazardous effects have been reported in several fish species leading to high mortalities and economic losses of the exposed ?sh. Even the lowest concentration of pyrethroid has the potential to paralyse fish and kill invertebrates. Despite lack of published scientific evidence here in Papua New Guinea, there are numerous cases with physical evidence relating to misuse of treated nets in freshwater environments for fishing. Invertebrates inhabiting freshwater (and marine) ecosystems are important contributors to global diversity. They play a key role in aquatic ecosystems. These roles include water puri?cation and ?ltering, processing of organic matter, recycling of nutrients, and mediating transfer of carbon through food webs. These services sustain the diversity of the freshwater environments, which in turn serve as the source of organic products for plants, animals, and human beings as well.
With introduction of pyrethroids into the waterways, the invertebrates are primarily affected. This creates a cascade of negative effects across the ecosystem. Thus, once freshwater ecosystem is disturbed, it loses its integrity as a biological system, resulting in stagnancy and stale bodies of water.
Threat to survival of organisms
This results in accumulation of pyrethroid toxicity, leading to severe consequences for the fitness, reproductive success, and survival of aquatic organisms, ultimately leading to population-level effects. An organism’s stress responses diverts its energy away from normal metabolic functions, resulting in “higher-level” effects such as growth inhibition and reduced reproductive success.
Freshwater ecosystems connect headwaters with oceans, land with water, and people with the resources they need to thrive. Along with food and shelter, they form our most basic need. Freshwater ecosystems are not only our source of water, they are fundamentally, our livelihoods. Healthy, functioning freshwater ecosystems provide reliable and quality water flows upon which these basic human needs depend.
Energy, food, and health, which are all indispensable to human development, rely on the services provided by natural freshwater ecosystems. Unfortunate, many rivers and streams that were once full of life and self-sufficiency, are now literally drying and void of life. This is the kind of trend now witnessed in aquatic ecosystems across coastal areas of Papua New Guinea.
We cannot deny that millions of lives are saved from malaria every year. But all at the same time, we should not turn a blind eye on negative impacts of misusing treated nets. Exposure of freshwater environments to pyrethroid insecticides is certainly a high risk issue, and its occurrence will continue to be an important ecological health concern.
However, we could all wonder if there might be better malaria control solutions – may be, specially treated wall coverings, custom-built window screens, DDT house spraying, or what else? Clearly, there are no easy answers.
Source of information”

• Farag, MR, et al. 2021, An Overview on the Potential Hazards of Pyrethroid Insecticides in Fish, with Special Emphasis on Cypermethrin Toxicity, Animals, 11 (1880), viewed 07 February 2022, https://doi.org/10.3390/ani11071880
• Nureye, D and Assefa, S 2020, Old and Recent Advances in Life Cycle, Pathogenesis, Diagnosis, Prevention, and Treatment of Malaria Including Perspectives in Ethiopia, Scientific World J, viewed 10 March 2022, https://doi.org/10.1155/2020/1295381
• Werner, I and Moran, K 2008, Effects of pyrethroid insecticides on aquatic organisms, ACS Symposium Series, viewed 24 January 2022, https://www.researchgate.net

Gelinde Narekine is a technical officer in the School of Medicine and Health Sciences, University of Papua New Guinea