A vector-borne disease is an infectious disease transmitted to humans or animals by blood-feeding arthropods, such as mosquitoes, ticks, fleas, or sand flies.
A disease vector is any living agent that carries and transmits an infectious pathogen such as a parasite or microbe, to another living organism.
Agents regarded as vectors are mostly blood-sucking insects such as mosquitoes.
These vectors carry pathogens—such as viruses, bacteria, or parasites—that are acquired from an infected host and subsequently transmitted to a new host during feeding.
These vectors can carry infectious pathogens such as viruses, bacteria, protozoa, and parasitic worms.
The pathogens often undergo part of their life cycle within the vector before transmission occurs.
Vector-borne diseases include malaria, dengue, Zika, chikungunya, Lyme disease, and Rocky Mountain spotted fever.
The transmission dynamics and geographic distribution of these diseases are influenced by the biology of the vector, environmental factors, and human activities.
Mosquito-borne diseases- Malaria, dengue, Zika virus, West Nile virus, chikungunya, yellow fever.
Tick-borne diseases-Lyme disease, Rocky Mountain spotted fever, anaplasmosis, babesiosis
Flea-borne diseases-Plague, typhus
Fly-borne diseases-Leishmaniasis, African trypanosomiasis
Vectorborne diseases account for more than 17% of all infectious diseases globally, causing over 700,000 deaths annually.
Malaria alone is responsible for more than 400,000 deaths each year, predominantly affecting children under five in sub-Saharan Africa.
Climate change is expanding habitat ranges for vectors.
Urbanization and population movement changing patterns of vectorborne diseases as has deforestation and other land-use changes.
There are inadequate vector control programs in existence.
Arthropods:
Mosquitos, flies, sand flies, lice, fleas, ticks, and mites transmitting a huge number of pathogens.
Many such vectors are haematophagous, which feed on blood at some or all stages of their lives.
When the insects feed on blood, the pathogen enters the blood stream of the host.
The Anopheles mosquito is a vector for malaria, filariasis, and various arthropod-borne-viruses (arboviruses).
The Anopheles mosquito inserts its delicate mouthpart under the skin and feeds on its host’s blood.
The parasites the mosquito carries are usually located in its salivary glands and are transmitted directly into the host’s blood stream.
Pool feeders-sand fly and black fly, are vectors for pathogens causing leishmaniasis and onchocerciasis respectively.
They chew a well in the host’s skin, forming a small pool of blood from which they feed.
Leishmania parasites then infect the host through the saliva of the sand fly, while Onchocerca force their own way out of the insect’s head into the pool of blood.
Triatomine bugs are responsible for the transmission of a trypanosome, Trypanosoma cruzi, which causes Chagas disease.
The Triatomine bugs defecate during feeding and the excrement contains the parasites, which are accidentally smeared into the open wound by the host responding to pain and irritation from the bite.
Several species of Thrips that act as vectors for over 20 viruses, especially Tospoviruses, and plant diseases.
Some plants and fungi act as vectors for various pathogens.
Many plant pests that seriously damage important crops depend on other plants, often weeds, to harbour or vector them.
When they twine from one plant to another, parasitic plants have been shown to convey phytoplasmal and viral diseases between plants.
Rabies is transmitted through exposure to the saliva or brain tissue of an infected animal.
Any warm-blooded animal can carry rabies, but the most common vectors are dogs, skunks, raccoons, and bats.
Rapid changes in land use, trade globalization, climate change and social upheaval are causing a resurgence in zoonotic disease across the world..
Displacement due to conflicts, migration, or population movements can create situations where people are more exposed to disease vectors.
Human activities such as deforestation, agricultural expansion, urbanization, and increased trade and travel, are creating environments where vectors can thrive and spread diseases to humans more easily.
Rising temperatures due to climate change create more favorable conditions for mosquitoes to expand their ranges and increase their populations, leading to higher rates of disease transmission in areas where these diseases were previously uncommon or nonexistent and the emergence of new diseases.
Vector-borne zoonotic diseases include:
Lyme disease: Caused by the bacterium Borrelia burgdorferi, it is transmitted to humans by infected black-legged ticks, often found in wooded or grassy areas.
Plague: Caused by the bacterium Yersinia pestis, it is primarily transmitted by fleas that infest rodents.
The plague disease has had significant historical impacts, including the Black Death.
West Nile virus: Transmitted by mosquitoes, it causes symptoms ranging from mild flu-like illness to severe neurological diseases, including encephalitis.
Factors influence the incidence of vector-borne diseases, including environmental conditions, animal hosts, and the movement of people.
The expansion of human settlements into previously undisturbed areas creates new habitats for vectors and animals that are potential hosts.
Vector-borne zoonotic diseases are transmitted by a variety of vectors, including arthropods (mosquitoes, ticks, fleas) and rodents, with humans often acting as incidental hosts.
It is estimated that over 80% of the world’s population resides in areas under threat of at least one vector borne disease.
Reducing vector-borne diseases.
Source reduction is the most effective long-term strategy.
This involves eliminating breeding sites for vectors, particularly standing water where mosquitoes reproduce.
Proper waste management prevents creating habitats for disease vectors.
Water management includes improving drainage systems, covering water storage containers, and treating water bodies when necessary.
Maintenance of swimming pools and proper irrigation practices also reduce breeding opportunities.
Physical barriers provide immediate protection.
Use of bed nets, especially long-lasting insecticidal nets (LLINs) for malaria prevention.
Wearing long-sleeved clothing and pants.
Repellents containing DEET, picaridin, or oil of lemon eucalyptus effectively deter vectors.
Indoor protection includes using air conditioning when available, installing window and door screens, and using fans which can disrupt mosquito flight patterns.
Vector control programs use integrated approaches combining multiple strategies.
Indoor residual spraying with insecticides, community education campaigns, and coordinated elimination of breeding sites across neighborhoods.
Surveillance systems monitor vector populations and disease transmission patterns.
Early detection allows for rapid response and targeted interventions.
Public health services ensures prompt diagnosis and treatment of vector-borne diseases, reducing the infectious reservoir in human populations.
Insecticides can be applied through space spraying during outbreaks, residual spraying on indoor surfaces, and larvicide treatment of breeding sites that cannot be eliminated.
Biological control uses natural predators, parasites, or pathogens to reduce vector populations.
Genetic approaches include sterile insect techniques and genetically modified mosquitoes to reduce vector populations or their ability to transmit pathogens.
Novel repellents.
Reducing vector habitat includes proper drainage, green space management, and building design that minimizes vector entry and breeding opportunities.
Climate adaptation strategies account for how changing temperatures and precipitation patterns affect vector distribution and breeding cycles.