Mosquitoes are the bane of the spring and summertime. The one aspect that is often not brought up when mentioning these pests is the danger that can be contained within a bite. Mosquitoes are the most important arthropods that affect human health. There are about 100 mosquito-borne diseases that affect humans globally. Here are a few of the most common diseases associated with mosquitoes.
Chikungunya is a mosquito-borne viral disease. It is believed to have origins from Tanzania. The name “chikungunya” derives from a word in the Kimakonde language, meaning “to become contorted”, and describes the stooped appearance of sufferers with joint pain. It occurs mainly in tropical and semi-tropical regions of the world. However, travelers to infected regions of the world can get infected when bitten by infected mosquitoes.
Mosquito Species Transmitting Chikungunya Virus
The most common type of mosquitoes involved in the transmission of the virus are the tropical mosquitoes Aedes aegypti and Aedes albopictus, two species which have often been associated with also transmitting other mosquito-borne viruses. These mosquitoes can be found biting throughout daylight hours, though there may be peaks of activity in the early morning and late afternoon. Both species are found biting outdoors, but Ae. aegypti will also readily feed indoors. Good news is that both species are not known to be established in Canada; though there has been some temporary sighting in some parts of the country .
After the bite of an infected mosquito, the incubation period for potential illness can range from 2 to 12 days.
- Joint pain
- Muscle pain
Not considered fatal in most cases as patients recover fully. There are occasional cases whereby complications have occurred. Serious complications are not common, however in older people, the disease can sometimes be fatal.
Dengue is a mosquito-borne viral disease that has rapidly spread across the globe in recent years, impacting 40 percent of the earth’s population (between 50 to 100 million people around the world) in areas where it is possible to contract Dengue. There are four viral types of dengue, but the most severe form of this disease is the Dengue Hemorrhagic Fever (DHF). DHF may result in death, especially among children, if not quickly and properly treated. Dengue causes a wide spectrum of disease. This can range from people who may not know they are even infected to more severe flu-like symptoms.
Mosquito Species Transmitting Dengue
The virus is transmitted to humans through the bites of infected female mosquitoes, primarily the tropical Aedes aegypti mosquito. Other species within the Aedes genus can also act as transmitters of the virus, but their contribution is secondary to Ae. aegypti.
In general, most cases are asymptomatic (meaning that people do not show symptoms).
But for those with symptoms, initial symptoms typically develop 3-7 days after being bitten by an infected mosquito. However, it may take up to 14 days for symptoms to appear.
- Severe headache
- Pain behind the eyes
- Muscle and joint pain
Should I be Concerned?
Most people who get infected with dengue virus are able to recover. According to Health Canada, about 2.5% of people who progress to further stages of Dengue end fatally.
Malaria is caused by a protozoan parasite plasmodium. Epidemiologists estimate that more than ½ million people die each year from malaria. Malaria occurs mostly in tropical and subtropical areas of the world and most of those who die are young children. In sub-Saharan Africa, malaria is commonly fatal to young children and pregnant women. Children usually have not developed the necessary immunities to fight the disease, and pregnant women often experience weakened immune systems along with decreased health in general.
Mosquito Species Transmitting Malaria
The malaria parasite is transmitted through the bites of infected female Anopheles mosquitoes. There are more than 400 different species of Anopheles mosquito; around 30 are malaria transmitters of major importance.
All of the important transmitter species bite between dusk and dawn. The intensity of transmission depends on factors related to the parasite, the specific mosquito, the human host, and the environment.
Symptoms of malaria are often similar to those of the flu, and include:
- Paroxysms of Fever
- Drowsiness and Fatigue
- Sweats or chills
- Nausea and vomiting
- Muscle and stomach pain
- Severe anemia
Although malaria can be a deadly disease, illness and death from malaria can usually be prevented. If left untreated, malaria has the potential lead to death.
West Nile Fever is another mosquito-transmitted disease caused by the West Nile Virus and was first detected in the United States in New York in 1999. Since then, the West Nile Virus has reached Canada, as well as Mexico.
West Nile Fever Transmission
Human infection is most often the result of bites from infected mosquitoes. Mosquitoes become infected when they feed on infected birds, which act as a host for the virus.
The virus eventually gets into the mosquito’s salivary glands. During later blood meals (when mosquitoes bite), the virus may be injected into humans and animals, where it can multiply and possibly cause illness. The virus is primarily transmitted by the mosquitoes from the genus Culex, particularly the Culex pipiens complex.
Some common symptoms of West Nile Fever can include:
- Body aches
- Mild rash
- Swollen lymph glands
The fatality of the virus depends upon how far along symptoms have progressed. As recovery from milder cases can take a week. As symptoms worsen and become more severe, there is a higher likelihood that fatality is possible.
Zika virus is a mosquito-borne flavivirus that was first identified in Uganda in 1947 in monkeys. It was later identified in humans in 1952 in Uganda and the United Republic of Tanzania.
Outbreaks of Zika virus disease have been recorded in Africa, the Americas, Asia and the Pacific. From the 1960s to 1980s, rare sporadic cases of human infections were found across Africa and Asia, typically accompanied by mild illness.
Zika virus is primarily transmitted by the bite of an infected mosquito from the Aedes genus, mainly Aedes aegypti, in tropical and subtropical regions. Aedes mosquitoes usually bite during the day, peaking during early morning and late afternoon/evening. This is the same mosquito species that transmits Dengue, Chikungunya and yellow fever.
Common symptoms of the Zika Virus include:
- Conjunctivitis (pink eye)
- Skin rash
- Joint and muscle pain
Zika virus infection during pregnancy can result in complications such as microcephaly and other congenital abnormalities in the developing fetus and newborn. Zika infection in pregnancy also results in pregnancy complications such as fetal loss, stillbirth, and preterm birth.
Zika virus infection is also a trigger of Guillain-Barré syndrome, neuropathy and myelitis, particularly in adults and older children.
Eastern Encephalitis (Eastern Equine Encephalitis)/ Western Encephalitis (Western Equine Encephalitis)
Eastern equine encephalitis (EEE) is a mosquito-borne virus found throughout the Western Hemisphere. The first human case of EEEV infection (eastern equine encephalitis; EEE) occurred in Massachusetts in 1938, yet EEE was initially recognized about a century earlier in horses.
Western equine encephalitis (WEE) is a member of the Alphavirus genus within the family Togaviridae. The virus was first recognized in a horse in California in 1930. Sporadic outbreaks have been recognized in Canada each decade since the 1930’s. The WEE virus has been reported across south-central Canada from approximately Lake Superior to the Rocky Mountains, but it also has occurred in British Columbia. Disease in humans and horses has occurred most often in Saskatchewan and Manitoba.
Mosquito Species Transmitting Encephalitis
Both viruses are transmitted naturally to humans from bites of infected mosquitoes of Aedes , Coquillettidia , and Culex species for EEE; and Ochlerotatus,, Aedes, and Culex species for WEE) which feed on both animals and humans.
Symptoms usually appear suddenly, starting with:
As symptoms worsen, they may also include:
- stiff neck
- general weakness
- movement disorders
- mental or behaviour changes
- paralysis (being unable to move)
- possible long-term nerve and brain damage
Should I be Concerned?
EEE has a mortality rate of between 50-75% in humans when symptoms worsen. For WEE, there is a 8-15% chance of mortality. There is no current cure for either virus, with treatment being a symptomatic approach. As the namesake of the virus, there is a 100% mortality in horses with both viruses.
St. Louis Encephalitis (SLE)
Saint Louis Encephalitis is a mosquito-borne flavivirus. This disease mainly affects the United States, including Hawaii. Occasional cases have been reported from Canada, Mexico and the Caribbean.
Mosquitoes Species Transmitting St. Louis Encephalitis
The most common mosquito species known to transmit SLE are Culex pipiens complex, Culex quinquefasciatus, Culex nigripalpus, Culex tarsalis and some Anopheles species
Symptoms of St. Louis Encephalitis
When infection is more severe the person may experience
- high fever
- neck stiffness
- coma, tremors, occasional convulsions and spastic paralysis.
Should I be Concerned?
The fatality rate for St. Louis encephalitis is between 5% to 15%. The risk of fatal disease increases with age and is about 20% in patients over 60 versus 3% to 6% in children and young adults.
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