Mosquito – A Vector for Diseases
Mosquitoes. They are lightweight, small, and barely visible flying insects
that buzz softly around your ears at night… as annoying as a jackhammer on a Sunday morning. You sometimes see one hovering right in front of you, taunting you until it finally disappears.
A few minutes later you discover an itchy bump that gets itchier when scratched.
If you are lucky.
Mosquitoes kill at least a million people every year – more than any other animal – and cause illness in millions more. Mosquito-borne diseases include:
- Chikungunya fever
- Zika fever
- Dengue fever
- Yellow fever
- Lymphatic filariasis
- West Nile virus
- Japanese encephalitis
Technically, these diseases are caused by viruses or parasites, not by mosquitoes. However, the mosquito acts as a “disease vector” – carrying the virus or parasite from one host to another.
The mosquito feeds on an infected person and acquires the disease-causing virus or parasite. When it feeds on another person, it can transmit the virus or parasite to that person.
Most mosquito-borne diseases occur in warmer climates, especially in Africa, South Asia, Central, and South America, the Caribbean, Oceania, the Middle East, and the Eastern Mediterranean.
Climate change has led to warmer temperatures and in some areas, more rainfall. This change is expected to result in more mosquito breeding sites, faster growth, and higher numbers of disease-carrying mosquitoes over a larger geographic range.
Infected mosquitoes have also increased their range by traveling on boats, cars, trains, and even planes.
Viruses and parasites have increased their range as well. They travel in infected people to areas where there are mosquitoes that can carry that parasite or virus. Those mosquitoes feed on the infected people and then transmit the parasite or virus to the next person they feed on.
The biggest risk factor for contracting a mosquito-borne disease is being in an area where the disease is present or where there was a recent outbreak.
People at risk for developing more serious disease include:
- Young children
- Older adults
- Pregnant women and their unborn infants
- People living in poverty
- People with limited access to health care
- People with pre-existing health conditions
Mosquito Bite Prevention
Aedes mosquitoes, which are responsible for transmitting several diseases, feed mainly during the day. The malaria-carrying Anopheles mosquitoes feed at night, often indoors. In areas with an endemic (constantly present) disease or outbreaks, it is important to be protected around the clock.
Nothing is foolproof, but there are ways to minimize your chances of getting a mosquito-borne disease.
1) Remove all sources of standing water around your home.
- Mosquitoes need standing water to breed. Everyday items such as a watering can, an unseen bottle cap under a chair, a clogged gutter, an uneven stretch of pavement, garbage cans, toys, and even the creases of a folded bag can all hold enough water to let mosquitoes breed.
- If you have a pond, pool, or birdbath keep it clean and make sure to have water constantly flowing.
- Clean and refill pet water bowls every day.
2) Wear loose clothing. Mosquitos can feed through tight-fitting clothing.
3) Wear clothing washed or sprayed with products containing permethrin, a mosquito repellent.
- Permethrin is safe on clothing but should not be applied directly to the skin. Some companies make clothes that are pre-sprayed with permethrin and can be washed many times without losing effectiveness.
4) Use mosquito repellent on exposed skin.
- The most effective are:
DEET is generally considered to be the most effective mosquito repellent. DEET is considered safe for infants over 2 months old, but it is important to read package directions and only apply once a day.
Picaridin in the 20% strength is roughly as effective as DEET but does not last as long. Like DEET, Picaridin can be used on infants over two months old.
PMD, found in products containing oil of lemon eucalyptus, is another effective option, although studies comparing it directly to DEET have had mixed results. PMD has not been tested on children younger than 3 years old.
- Less effective:
-Citronella. Citronella requires frequent re-application
- Not effective:
-Botanical oils, other than oil of lemon eucalyptus and to some degree, citronella.
-Repellent bracelets (including those with DEET)
-Electronic repellents that use high pitched sounds to repel mosquitos.
-Eating strong-smelling foods such as garlic or onions.
5) Mosquito netting
Sleep under mosquito netting tucked under the mattress if you are outdoors or if your room does not have intact screens or air conditioning. Netting that has been recently treated with repellent is the best choice. Even the best netting will be ineffective if there are holes or gaps.
Before traveling it is important to find out what diseases are present in the area and if there are any special precautions you should take. Although on the surface mosquito-borne diseases have a lot in common, understanding each one individually can mean the difference between life and death. We highlight three of the most common diseases, malaria, zika fever, and dengue fever, below.
Mosquito-borne disease #1: Malaria
Malaria, caused by a parasite, kills roughly 500,000 people every year and sickens approximately 219 million.
After repeated exposure, older children and adults develop some protection against severe disease. However, that protection is lost if the person moves to an area where the disease is uncommon and exposure is infrequent, or if the species of the malaria parasite is different.
Signs and symptoms of malaria usually begin between 8 days and 4 weeks after a bite. However, some malaria species can remain in the body for up to a year before causing symptoms such as:
- Fever with or without delirium
- Nausea, vomiting, diarrhea
- Muscle pain
- Joint pain
- Chest or abdominal pain
- Rapid heartbeat
Some species of the malaria parasite can cause a more severe form of malaria, leading to:
- Fluid in the lungs
- Kidney failure
- Altered consciousness
- Liver failure
- Ruptured spleen
- Blood clotting and/or bleeding
- Low blood sugar
Without appropriate treatment, some types of malaria will stay in the liver for up to four years.
Malaria is diagnosed with a medical history, physical exam, and blood test showing the presence of the parasite. Because symptoms can mimic many other conditions, a blood test is important in confirming the diagnosis and if possible, identifying the species of the malaria parasite.
Malaria is treated with medications called antimalarials. Where the parasite is not resistant to chloroquine, that is the medication of choice. Where the parasite is resistant, or, becoming resistant, artemisinin-based combination therapies (ACTs) are used.
Depending on the circumstance, an additional antimalarial might be recommended.
Anti-malarial drugs can be taken in advance of travel to countries where malaria is present. The CDC has an up-to-date list of countries with malaria and recommendations on the most effective anti-malaria drug.
Other risk factors
- Risk is increased with blood transfusions, organ transplantation, and sharing used hypodermic needles
- The highest mortality rate is seen in children on the African continent.
- Pregnant women can pass the disease on to an unborn child or deliver an infant with low birth weight and anemia.
Mosquito-borne disease #2: Zika Fever
Zika fever is caused by a virus transmitted by the bite of an Aedes mosquito. It can also be transmitted from human to human through unprotected sex.
Only around 20% of infected adults develop symptoms. These typically last for 2-7 days and include:
- Low-grade fever
- Itchy rash
- Joint pain, often in the small joints of hands and feet
- Conjunctivitis (dry)
Although symptoms are relatively mild and short-lasting, Zika virus can have severe consequences when acquired during pregnancy, including miscarriage, preterm birth, stillbirth, and congenital malformations collectively known as congenital Zika syndrome.
Babies born with congenital Zika syndrome may have:
- Microcephaly (a small head with an underdeveloped brain)
- Muscle stiffness
- Vision damage
- Limited range of joint motion
- Hearing loss
Complications of Zika fever in adults and children are neurological and include nerve damage, myelitis (spinal cord inflammation), and Guillain Barre syndrome.
Asymptomatic people who have been exposed to Zika are not ordinarily tested unless they are pregnant. Symptomatic people who have been in an area where the virus is or was present will have a urine or blood test.
Zika fever can look like dengue fever or chikungunya. Testing is often done for all three at the same time.
There are no medications specifically for the Zika virus. Treatment consists of fluids, rest, and acetaminophen (such as Tylenol or Paracetamol). Antibiotics are not effective against viruses and should not be taken.
Condoms are extremely important in preventing transmission to women who are pregnant or could become pregnant.
Pregnant women or women trying to get pregnant should not travel to areas where there is or has been an outbreak.
The CDC has excellent information on the sexual transmission of Zika virus.
Additional risk factors:
Zika virus can be transmitted through blood transfusions, organ transplantation, or needlesticks. Transmission through blood is uncommon.
Mosquito-borne disease #3: Dengue Fever
Like the Zika virus, dengue viruses are transmitted through the bite of an infected Aedes mosquito. There are four types of the virus. Developing immunity to one type does not provide immunity to the other three.
Symptoms include a fever of at least 101.3 degrees Fahrenheit or 38.5 degrees Celsius plus at least two of the following:
- Muscle, bone, or joint pain
- Nausea or vomiting
- Pain behind the eyes
- Swollen glands
Not everyone develops symptoms. Those who do typically recover within 2-7 days. However, some people will develop severe dengue (also known as dengue hemorrhagic fever or dengue shock syndrome), a life-threatening condition that requires immediate medical attention.
Symptoms of severe dengue include:
- severe abdominal pain
- persistent vomiting
- rapid breathing
- bleeding gums or a nosebleed
- cold or clammy skin
- blood in vomit, urine, or stool
- low blood pressure
People who have already been infected by one dengue virus are at higher risk of developing severe dengue if they are infected by another dengue virus.
Diagnosis of dengue fever is based on a medical history and physical exam, symptoms, and a blood test.
There is no specific treatment for dengue. Again, the recommendations include rest, fluids, and acetaminophen or paracetamol. Aspirin and other non-steroidal anti-inflammatory drug (NSAIDS) such as ibuprofen should not be used because of the risk of bleeding.
People with symptoms of severe dengue should be treated by medical professionals experienced in the care of people with dengue. That experience can reduce the risk of mortality from 20% to 1%.
A vaccine is available in approximately 20 countries. The vaccine is only advised for people who have already been exposed to one of the four dengue viruses.
Additional risk factors:
- A pregnant woman can pass the virus on to the baby during pregnancy or delivery.
- One case of transmission through breast milk has been confirmed.
- Dengue can be transmitted through blood transfusion, organ transplantation, or shared needles, but it rarely happens.
A Bit More Information
As you read this, you might have wondered why mosquitoes transmit some viruses and parasites, but not others. One reason is that many viruses and parasites don’t survive inside mosquitoes, or inside of all types of mosquitoes.
As an example, mosquitoes can’t transmit the human immunodeficiency virus (HIV). HIV doesn’t survive or replicate well in mosquitoes. By the time a mosquito is ready for its next blood meal, the virus is no longer a threat.
However, the diseases that mosquitoes can and do carry are a tremendous threat.
They cause a million deaths every year, millions of cases of severe illness and suffering, and billions of dollars in expenses, lost income, and productivity every year. It’s unimaginable but very real.
Protect yourself by knowing the risks where you live or travel.
Follow our suggestions for avoiding mosquito bites and disease transmission. You might avoid some itching, or you might avoid a life-threatening illness.
How Halza Can Help
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