General Health
Vector-Borne Diseases: Environmental, Human Health, and Ecological Connections
August 23, 2017
Vector-borne diseases are illnesses
caused by pathogens and parasites in human populations. Every year there are
more than 1 billion cases and over 1 million deaths from vector-borne diseases
such as malaria, dengue, schistosomiasis, human African trypanosomiasis,
leishmaniasis, Chagas disease, yellow fever, Japanese encephalitis and
onchocerciasis, globally.
Vector-borne diseases account for
over 17% of all infectious diseases.
Main
vectors and diseases they transmit
Vectors are living organisms that
can transmit infectious diseases between humans or from animals to humans. Many
of these vectors are bloodsucking insects, which ingest disease-producing
microorganisms during a blood meal from an infected host (human or animal) and
later inject it into a new host during their subsequent blood meal.
Mosquitoes are the best known
disease vector. Others include ticks, flies, sandflies, fleas, triatomine bugs
and some freshwater aquatic snails.
Mosquitoes
- Aedes
- Chikungunya
- Dengue fever
- Rift Valley fever
- Yellow fever
- Zika
- Anopheles
- Malaria
- Culex
- Japanese encephalitis
- Lymphatic filariasis
- West Nile fever
Sandflies
- Leishmaniasis
- Sandfly fever (phelebotomus fever)
Ticks
- Crimean-Congo haemorrhagic fever
- Lyme disease
- Relapsing fever (borreliosis)
- Rickettsial diseases (spotted fever and Q fever)
- Tick-borne encephalitis
- Tularaemia
Triatomine
bugs
- Chagas disease (American trypanosomiasis)
Tsetse
flies
- Sleeping sickness (African trypanosomiasis)
Fleas
- Plague (transmitted by fleas from rats to humans)
- Rickettsiosis
Black
flies
- Onchocerciasis (river blindness)
Aquatic
snails
- Schistosomiasis (bilharziasis)
The World Health Organization (WHO) states that control and prevention of vector-borne diseases are emphasizing "Integrated Vector Management (IVM)",which is an approach that looks at the links between health and environment, optimizing benefits to both.
In April 2014, WHO launched a campaign called “Small bite, big threat” to educate people about vector-borne illnesses. WHO issued reports indicating that vector-borne illnesses affect poor people, especially people living in areas that do not have adequate levels of sanitation, drinking water and housing.
For diseases where there is no effective cure, such as Zika
Virus, West Nile Virus and Dengue fever, vector control remains the only way to
protect human populations.
However, even for vector-borne diseases with effective
treatments the high cost of treatment remains a huge barrier to large amounts
of developing world populations. Despite being treatable, malaria has by far
the greatest impact on human health from vectors. In Africa, a child dies every
minute of malaria; this is a reduction of more than 50% since 2000 due to
vector control. In countries where malaria is well established the World Health
Organization estimates countries lose 1.3% annual economic income due to the
disease. Both prevention through vector control and treatment are needed to
protect populations.
As the impacts of disease and virus are devastating, the
need to control the vectors in which they carried is prioritized. Vector
control in many developing countries can have tremendous impacts as it
increases mortality rates, especially among infants. Because of the high
movement of the population, disease spread is also a greater issue in these
areas.
As many vector control methods are effective against
multiple diseases, they can be integrated together to combat multiple diseases
at once.[5] The World Health Organization therefore recommends "Integrated
Vector Management" as the process for developing and implementing strategies
for vector control.
Methods
Vector control focuses on utilizing preventative methods to
control or eliminate vector populations. Common preventative measures are:
Habitat and environmental control
Removing or reducing areas where vectors can easily breed
can help limit their growth. For example, stagnant water removal, destruction
of old tires and cans which serve as mosquito breeding environments, and good
management of used water can reduce areas of excessive vector incidence.
Further examples for environmental control is by reducing
the prevalence of open defecation or improving the designs and maintenance of
pit latrines. This can reduce the incidence of flies acting as vectors to
spread diseases via their contact with feces of infected people.
Reducing contact
Limiting exposure to insects or animals that are known
disease vectors can reduce infection risks significantly. For example, bed
nets, window screens on homes, or protective clothing can help reduce the
likelihood contact with vectors. To be effective this requires education and
promotion of methods among the population to raise the awareness of vector
threats.
Chemical control
Insecticides, larvicides, rodenticides, Lethal ovitraps and
repellents can be used to control vectors. For example, larvicides can be used
in mosquito breeding zones; insecticides can be applied to house walls or bed
nets, and use of personal repellents can reduce incidence of insect bites and
thus infection. The use of pesticides for vector control is promoted by the
World Health Organization (WHO) and has proven to be highly effective.
Biological control
The use of natural vector predators, such as bacterial
toxins or botanical compounds, can help control vector populations. Using fish
that eat mosquito larvae or reducing breeding rates by introducing sterilized
male tsetse flies have been shown to control vector populations and reduce
infection risks.
Legislation
In the United States, cities or special districts are
responsible for vector control. For example, in California, the Greater Los
Angeles County Vector Control District is a special district set up by the
state to oversee vector control in multiple cities.
References
"Vector". WordNet Search 3.1. Princeton University. Retrieved 7 April 2014.
"WHO Malaria". World Health Organization. 2015.
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