Vector borne diseases are human illnesses that are caused by parasites, viruses, and bacteria that are transmitted by mosquitoes, sandflies, triatomine bugs, blackflies, ticks, tsetse flies, mites, snails and lice. Each year there are more than 700,000 deaths from diseases like malaria, dengue, schistosomiasis, yellow fever and others on a global scale.
The prominent vector borne diseases, when combined account for about 17 percent of all infectious diseases. Vector bone diseases are worst in tropical and subtropical areas and they affect the poorest populations disproportionally. In 2014, many critical outbreaks of dengue, malaria, chikungunya, yellow fever and Zika have hit populations and overtaken health systems in many countries.
The distribution of vector borne diseases is based on a variety of factors like demographics, environmental and social components. Travel and trade globally, urbanization and environmental problems like climate change have impacted vector borne pathogen transmission. Climate change is making transmission season longer and more intense in some countries. It is also causing diseases to emerge in places they were not previously known.
Further climate change has affected agricultural practices and seasons which vary in temperature and rainfall which in turn affects the transmission of the vector disease. The spread of urban slums which lack piped water or reasonable waste management can put large groups of people in cities at risk of viral diseases which are spread by mosquitoes. These factors combined affect the reach of vector populations and transmission patterns of disease-causing pathogens.
How Do Vectors Spread Disease?
Vectors are living organisms that are able to transmit infectious diseases between humans and from animals to people. A lot of these vectors are bloodsucking insects that eat disease producing microorganisms during a meal when they are sucking blood from an infected host (human or animal) and later inject it into a new host during their next blood meal.
Mosquitoes are the most known disease vector. But other well-known vectors include ticks, flies, sandflies, fleas and some freshwater aquatic snails.
There is no credible evidence that you can get Lyme disease from mosquitos. Rather Lyme disease is transmitted by infected ticks.
Malaria causes more than 400,000 deaths every year around the world, most of which are children under five years old.
Factors That Must Be Present for Disease to Occur
Arthropod vectors are cold-blooded which means they are extremely sensitive to climate factors. Weather and thus climate changes affect the survival and reproduction of vectors. That, in turn, influences the sustainability, strength, distribution and intensity of vector activity which includes biting rates. This also affects the development and continuation of pathogens inside of vectors.
Other factors that affect vector distribution are habitat destruction, land use, pesticide application, and host density.
The prevalence of a vector borne disease is influenced by hot and cold temperature extremes and precipitation patterns.
The main factors that must be present are the correct environmental, social and demographic components for vector borne diseases to occur. Climate change can alter the transmission of vector borne diseases but other factors like how pathogens adapt and change, the availability of hosts, changing ecosystems, demographics and human behavior all factor in to the equation. The complexity of these interactions makes it difficult to pinpoint the exact measures needed for the vector borne diseases to survive and occur.
United States Vector
There are currently 14 vector borne diseases that are a national public health concern in the United States. These diseases contribute to a significant number of human illnesses and deaths each year.
The disease vector has created a threat to public health in the United States and interagency governments are required to report vector borne diseases to track the impact. In recent years many vector borne diseases have been introduced or reintroduced to the United States. They include the West Nile virus, the dengue virus and the chikungunya virus.
The West Nile virus is the main cause of mosquito-borne disease in the United States. From 1999 to 2013 almost 40,000 cases of the West Nile virus disease were reported. The first outbreak occurred in 1999 in New York City and has occurred every year since. Since it was first introduced into the United States, the WNV spread west and by 2004 it was active throughout the contiguous United States. The annual WNV activity continued to be stable through 2007 but declined through 2011 until it increased again in 2012. This drew questions about the factors that impact the variation from year to year.
The majority of people infected with the WNF do not show any symptoms of the disease. Peak transmission of the WNF to humans in the United States happens normally between June and September during the summer when mosquitoes are very active and temperatures are high.
Lyme disease is the other prominent vector borne disease in the United States which is passed on by the tick.