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The Effects of Climate Change on Neglected Tropical Diseases (NTDs)

Hi all, Gabby here! Over the summer I was able to attend an epidemiology/public health course at Brown University. It was such a great experience researching the connection between climate change and public health with neglected tropical diseases. I know most of you all don't know what NTDs are, but they're a type of disease that are prevalent in tropical areas; they impact more than a billion people from impoverished communities, and they're called "neglected" because they are absent from the global health agenda.

For our final, I wrote a paper on the effects of climate change on some specific neglected tropical diseases. Feel free to read!

Being responsible for affecting more than a billion people globally, it is still surprising that most do not know about NTDs. Hence, the reason why these diseases are called neglected tropical diseases; lack of education, awareness, and stigma against neglected populations are among the many reasons why these diseases affect the unlucky. Hidden, unexpected factors like climate change play a role in the spread. There are rising efforts on tackling the problem of accessibility such as Universal Health Coverage (UHC), but NTDs are “almost absent from the global health agenda” as the World Health Organization states. These families are greatly marginalized; so, it seems nothing but explanatory that the UHC would benefit since it focuses on the “full spectrum” from services to rehabilitation. If this reality comes true, relief will spread more rapidly compared to how the full list of NTDs wipe out communities. Several of these common diseases taking loved ones away from families are lymphatic filariasis, schistosomiasis, and onchocerciasis.

Lymphatic filariasis, also known as elephantiasis, is transmitted through infected mosquitoes that receive it from people they have previously fed on, resulting in a chain reaction. The disease itself is caused by filarial worms known as Wuchereria bancrofti, Brugia malayi, and Brugia timori; they are also known as the culprits to the disruption that occurs in the body’s lymphatic system–causing changes in our fluid balance and ability to fight infections (WHO). Like any other species, they mate to produce offspring which are released in the blood and soon mature to live up to seven years. Swelling in areas like arms and legs start becoming uncomfortably bigger while the fear factor rises. It is understandable how many people are focused on the spread of lymphatic filariasis through mosquitoes transmitting disease they pick up from those infected, but as mentioned before, the unthought factor of climate change plays a role. Climate change has always been a concern over the years as permanent changes in temperatures and weather patterns occur. Determining factors to the prevalence of lymphatic filariasis revolve around temperature and weather. Since the disease is most common in subtropical and tropical areas like Asia and Africa especially, it is the right environment for mosquitoes to thrive; they prefer humid, warm climates that are not too hot to stop their activity. With climate change’s impact in increasing the global temperature, it would allow mosquitoes to spread the disease while increasing the rates of reproduction. Life cycles for mosquitoes occur faster in warmer temperatures, meaning that eggs are laid more frequently and hatch. The increasing spread of lymphatic filariasis is inevitable and climate change’s rising temperatures can only be slowed by a number of ways. Besides climate change posing a threat in spreading the disease, it directly affects vulnerable populations. Vulnerable populations include those especially living in tropical or subtropical countries where lymphatic filariasis is common, poor populations, those living in remote communities, and children. Tourists can also be at risk for infection only if they stay in those areas for several months or years (CDC). A big factor that directly impacts vulnerable populations is that even though the parasite persists in internal damage, most infected people are asymptomatic or do not show symptoms. People do not realize they have lymphatic filariasis until symptoms, such as lymphedema or elephantiasis develop–causing problems in being able to receive immediate help. Access to treatments, medication, and medical support are all insufficient for poor, remote communities affected. Treatments like Diethylcarbamazine (DEC) help to kill the microfilariae and adult worms, but without health resources, obtaining these remedies are nearly impossible. With rises to this disease, communities would be infected as a whole without knowledge about remedies to help. Apparent symptoms (like elephantiasis) can worsen to damaging other organs and without a known cure, even learning and doing symptom management would only do so much. The body is already susceptible to bacterial infections while fluid buildup and skin hardening persists (CDC). Especially in children, risks of the disease worsening would be much higher as their bodies are overall more susceptible to dangers like these. Overall, lymphatic filariasis is impacted by climate change in the sense of providing a better environment for infected mosquitoes to expand and also cause more difficulty in management for vulnerable populations that do not have resources available.

Another common NTD is schistosomiasis, also known as bilharzia, which is caused by parasitic worms and are transmitted through contact with freshwater in which snails carry schistosomes. The parasites start penetrating skin after infected people urinate or defecate in the water–providing the best environment for parasites to grow in the snails and release into the water. Systems of the body react to the parasitic worms’ eggs and symptoms can build up over time; from starting off as a minor fever, damaging vital organs like the lungs after years can be a possibility come true (CDC). Around 237 million people around the world are affected, and only 105 million out of that total have been able to be treated. The number of cases increase in developing countries and are starting to even spread to urban areas because of eco-tourism (WHO). But, another reason behind this is what comes with climate change. Similar to how mosquitoes thrive in warm climates, parasitic worms that develop inside the snails can still survive and increase along with global warming temperatures. Transmissions for parasitic diseases are predicted to rise, causing more vulnerable populations in Africa, South America, the Middle East, and Asia to be affected by schistosomiasis. Climate change is also contributed by our actions as a community, which can impact the spread of the disease. Actions such as urbanization and deforestation into remote areas not only create emissions from releasing carbon, but it also introduces new populations and areas to schistosomiasis. Humans are invading animals’ habitats, making exposure to reservoirs easy from denser human populated areas. This is similar to the consequence of eco-tourism, which is expanding vulnerable populations along with an increase in prevalence. Many children, fishers, agricultural and domestic workers, and poor communities make up the vulnerable populations that need access to treatments and preventative action for care. The rising spread of schistosomiasis would only affect negatively; transmissions would rise when there are little resources available. Bodies of water in which children play, fishermen make a living out of, and where families do daily tasks at, would be infected–shutting off parts of everyone’s lifestyle. With current progress on schistosomiasis control in many countries, families and communities are still going to be impacted the most. Without domestic workers, men, and women providing for their families, towns can fall apart, and schistosomiasis can worsen to be an everyday problem–making a never-ending cycle of complications in eradicating schistosomiasis.

Onchocerciasis, also known as river blindness, shares common characteristics with lymphatic filariasis and schistosomiasis as an NTD. Similar to the other NTDs, onchocerciasis is also caused by a parasitic worm: Onchocerca volvulus. Transmission also happens through bites, like lymphatic filariasis, but through blackflies that live near rivers in remote villages. With the ability to become infective in a span of a week, the onchocerciasis larvae are deposited to the bitten area during the fly’s blood meal. The larvae grow around twelve months later, living near joints, muscles, and in fibrous nodules while constantly releasing new larvae. Symptoms range from itchiness, disfiguring skin disease, and the possibility of blindness (CDC). Mass drug administration with ivermectin is one of the current actions done to eliminate the disease, but to eliminate it fully, up to fifteen years of annual treatment are required in majorly endemic areas. Most of the endemic areas are in African countries in which more than ninety-nine percent are infected; with preventative measures existing, these populations still do not have access to treatments, healthcare officials, or help. It is estimated in 2017 that around 20.9 million people were infected with onchocerciasis worldwide from The Global Burden of Disease Study (CDC). Fortunately, there is a reduced risk of severe symptoms and infection from control programs that limit the blackfly population, but climate change is always a contributing factor to cases. Blackflies are usually fond of humid and hot days, which means prevalence of onchocerciasis would increase with warmer temperatures. Just like mosquitoes, blackflies would have more time to reproduce and spread the disease to more areas. Along with that, urbanization for supply increase would involve new populations settling near streams in remote, rural communities–introducing the infectious disease and causing outbreaks. The expansion into animals’ habitats comes with impacts for both sides; for humans, the close contact with animals result in increased cases of prevalent diseases in untouched areas. Increased cases can unintentionally increase the spread in rural villages consisting of all vulnerable populations: residents near rivers, those in tropical areas like Africa and Latin America, children, workers stationed in rivers, and women that do daily tasks near streams. These communities when experiencing symptoms do not have medical professionals nearby. If they happen to receive help, it would be difficult to have healthcare let alone be treated in health facilities. Within the vulnerable populations during increases of spread, the fear factor would increase as symptoms worsen over time; the fear factor builds up as a lack of education about diseases, possible symptoms, and at-home remedies about these common prevalent diseases still persist.

With consistent efforts over the years to educate the world about neglected tropical diseases, organizations are taking the chance to provide solutions to keep transmissions under control. But, when it comes to healthcare options and accessibility for everyone, these neglected tropical diseases are often left out of the picture. In addition to that, our contributions to climate change indirectly increases the spread of diseases that most of us are unaware of–simply because it does not directly affect us. Privileges need to be used to progress toward available treatments, vector control, and education within vulnerable populations instead of ignorance. The greater the risk of transmission, the more difficulty remote communities would experience. The NTDs persist to be a never-ending battle to eliminate.

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