Manmade Triggers Behind the Zika Virus

by Katy Schaefer

It seems that every year has its own health crisis. In the past ten years, we have seen panic from SARS, Mad Cow Disease, Bird and Swine Flu just to name a few.This year seems to be the year of the Zika Virus. Although the disease changes all the time, the panic is always the same. People want to know where it comes from, how it can be treated, and how it can be transmitted. But these aren’t the questions we should be asking. What we really need to know is what is causing the disease and is there a way we can make ourselves less susceptible to it? Recently scientists have been looking into the rising rates of diseases like Zika and Malaria and have found a surprising result. We might be doing this to ourselves, here’s how.

The first confirmed case of the Zika virus came out of Brazil in May of 2015. It is passed through mosquito bites and common symptoms include fever, rash, joint pain, and conjunctivitis. Hospitalization is uncommon, but there is currently no cure and there were reported links between the disease and birth defects in children born to infected mothers. However, most cases of Zika have been sprouting up primarily in South America, the Caribbean, and Africa. Researchers want to know why here, and why now? It is becoming clear that human intervention in the natural environment is impacting not only the viruses that infect our communities, but the insects that spread them.

The Aedes aegypti mosquito, also infamously known for spreading diseases like dengue and yellow fever, is also carrying and spreading Zika. This particular mosquito thrives in unique environments. “It doesn’t live in the ground, or in swamps, or any other kinds of places where you would normally find mosquitoes… So humans have created an environment for it to proliferate, by having all of these water containing containers around, and the mosquito has adapted so well…it’s really kind of a human parasite. It’s like the cockroach of the mosquito world” said Durland Fish, professor of microbial diseases at Yale University. Namely, they survive in tires, cans, and plastic containers. These are symptoms of not only poverty, but environmental degradation. However, the poor aren’t the only people being affected. The mosquitos can live in flower pots or water collected on a pool cover. Of course there are other factors that contribute to the spread of diseases like this, such as planes that can carry people and their diseases across oceans. Poverty that limits peoples ability to prevent and treat illness in a timely fashion to keep it from disseminating. But it’s more about the fact that while these factors have been discussed very openly, the environmental causes have been neglected.

An often looked over cause is the building of dams. While there have been widespread complaints about the ways damming a river might effect its ecosystem, with regards to the spread of disease, it is most problematic in that it brings people and disease together. Schitsomiasis is spread by parasite crying snails that live in freshwater. The Schistosomiasis outbreak in Ghana was catastrophic and widely blamed on the emergence of a dam. “More than 200 million people are infected worldwide. In terms of impact, this disease is second only to malaria as the most devastating parasitic disease. Schistosomiasis is considered one of the Neglected Tropical Diseases (NTDs)” ( Malaria alone is responsible for 1.1 million deaths per year and the building of dams only exacerbate the issue. Because the water is still and calm once it has been dammed, it acts as a habitat for the mosquitos.

Another trigger for the spread of diseases like Zika has been the rampant cutting down of forests. The removal of trees that used to act as a sort of barrier between people, animals, and insects. With the massive removal of these trees, the way that we interact with these living creatures is changing, and making humans more susceptible to disease. “In Malaysian Borneo over the past few years, scientists started to suspect that’s what was happening when they noticed an uptick in a form of malaria, caused by the parasite Plasmodium knowlesi, historically found mainly in macaques. In the last decade, research has shown that P. knowlesi has become the leading cause of human malaria in the region” (Chelsea Harvey). Although the parasite is found in macaques, it is still passed by mosquitos that live on, or near them. Scientists concluded that it was an environmental disturbance that brought people and these parasites together. And indeed it was, “forest clearing and development are actually causing people and mosquitoes and macaques to be in much closer contact than before” said Kimberly Fornace, research fellow at the London School of Hygiene and Tropical Medicine. Because of something called the “edge effect”, when ecosystems experience a high level of change at the edges of the habitat, these are also the most critically challenged areas when it comes to the spread of disease, where people and macaques come into contact. Additionally, the fact that these deforested areas tend to be hotter is affecting the spread of these diseases. Because they lack the cooling benefit of the trees, certain parts of the mosquito life cycle have been changing. In particular, the blood feeding and egg laying cycle of female Anopheles gambiae is shortened by up to 52%, greatly affecting the overall population of the insect.

Lastly, climate change has been influencing the survivable temperatures globally, broadening the regions that these mosquitos can live in. “Globally, temperature increases of 2-3ºC would increase the number of people who, in climatic terms, are at risk of malaria by around 3- 5%, i.e. several hundred million,” concludes the WHO. “Further, the seasonal duration of malaria would increase in many currently endemic areas.” Beyond this, mosquitos reproduce more quickly, and bite more frequently in the heat.

It is clear that there is a relationship between the environment and the spread of diseases like Schitsomiasis, Zika, and Malaria. The rising temperatures have expanded the regions that mosquitos are able to occupy. the damming of rivers has created massive pools of still water that not only attract mosquitoes, but bring parasite infected snails to the people that swim in it. Yet, it is still one of the least talked about factors in the spread of disease. It has become clear that we need to think about disease from a more ecological standpoint. Rather than rushing into the vaccination process, we should think more critically about the environmental factors that could be preventative. With these diseases in particular, it all comes down to the mosquitos, and treating them is just about as important as treating the people.



The Influence of Climate Change on global distributions of Dengue and Chikungunya Vector Species

by Kaylee Anderson

The global distribution of human cases of dengue and other mosquito-transmitted disease presents a serious health problem, especially considering the diseases have spread significantly in recent years. Although there is considerable research on the global distribution of these diseases, there is a second concern: range expansion by vector species. In recent years, the two main mosquito vectors, Aedes aegypti and albopictus have spread to more regions, including lower and middle latitudes, introducing ‘forest diseases’ to humans. Ae. aegypti is thought to be responsible for most massive outbreaks of dengue, so its future geographical distribution is important to predict. Continue reading

Asian Tiger Mosquito Targets Humans and Pets

by Emil Morhardt

As a follow-on to the previous post, this paper was just published a week ago and makes it clear that all the targets of Asian Tiger Mosquitos—transmitters of dengue, La Crosse, and chikungunya viruses in the Northeastern US—are mammals, and most of them are humans, cats, and dogs. Humans were targeted more in the suburbs, and cats in the cities. This is quite different from Culex mosquitos, another major vector of human diseases, which primarily feed on birds. Ari Faraji and his coauthors found this out by trapping mosquitos in central New Jersey, then sequencing the DNA in their blood meals. Mammalian blood constituted 84% of the meals, with humans making up 52%, cats 21%, and dog 12%. The rest came from mammals also, including, opossums, squirrels, rabbits, and deer.

Central New Jersey is at the northern limit of these mosquitos at the moment, but climate Continue reading