Offshore Living - Bugs and Bities


Mosquitoes

An article from Sydney University and providing useful info on how to best manage them. 

The following article was complied with information from the Department of Medical Entomology, University of Sydney & Westmead Hospital.


Overview

There are over 300 species of mosquito in Australia but less than 20 represent a risk to humans, either as nuisance-biting pests or carriers of disease.

When mosquito populations are high, biting may be experienced at any time of the day but, generally, mosquitoes are most active at dawn and dusk. In Far North Queensland the dengue mosquito will bite throughout the day.

During the warmer months, mosquitoes can take less than one week to complete their development from eggs to adults. Adult mosquitoes typically live for up to 3 weeks. Blood feeding on humans or animals provides the protein required for egg development, therefore only female mosquitoes bite. Mosquitoes are primarily attracted to carbon dioxide and the “smell” of our skin. Each mosquito species varies in its propensity to bite humans. People can vary in both their attractiveness to mosquitoes and their sensitivity to a mosquito bite. Mosquitoes rarely emerge infected with a virus, they must acquire it from feeding on an infective animal and the virus must infect the mosquito (a complex process that may take up to 10 days) before the virus can be transmitted to a human.

Mosquito myths and misconceptions

There is no scientific evidence that eating or drinking any particular food e.g. bananas or garlic can reduce the likelihood of being bitten by mosquitoes. There is no scientific evidence that taking vitamin B will reduce the likelihood of, or lessen the severity of an individual’s reaction to, a mosquito bite. Mosquitoes cannot transmit HIV or any disease other than specific mosquito-borne viruses. Blood type and skin colour are generally not good predictors of the likelihood of being bitten. Any activity (e.g. exercise) that increases body temperature or causes sweating may increase the risk of being bitten by mosquitoes. Studies show that pregnant women may be more likely to be bitten by mosquitoes due to increased body temperature. Studies have shown that the consumption of alcohol may increase the risk of being bitten by a mosquito due to increased body temperature.


Insect repellents

As well as the use of repellents, wearing loosely fitting long pants and long sleeved shirts will assist in reducing the number of mosquito bites received. Clothing can also be pre-treated with insecticides (e.g. permethrin) for added protection.

Insect repellents assist in preventing bites by repelling mosquitoes or inhibiting the mosquito’s stimuli for blood feeding. The stronger the concentration of an insect repellent, the less frequently it will need to be applied to stop mosquito bites Repellents containing low concentrations of DEET or Picaridin, if applied correctly, should stop mosquito bites for around two hours The formulation (e.g. roll-on, spray or lotion) doesn’t influence the product’s effectiveness as long as the repellent itself is evenly applied to the skin”

All insect repellents should be registered with the Australian Pesticides and Veterinary Medicines Authority (APVMA) before being made available for sale. Over 60 individual repellent formulations are currently registered. Brand names may vary but there are three main categories of repellents available; synthetic chemicals (DEET, picaridin and PMD), botanically derived products (e.g. Eucalyptus, Citronella, Melaleuca) and “wearable” devices. Wearable patches and wrist bands, typically impregnated with botanical products, do not offer effective protection from mosquitoes.

DEET (diethyltoluamide) was developed by the US Army in the 1950s and is the most widely used and effective repellent. In Australia, it is available in formulations ranging from than 10% up to 80%.

Picaridin (also known as Icaridin) was developed in the 1990s and while proven to be as effective as DEET, is generally thought to have a more pleasant scent. In Australia, it is available in formulations ranging from 10% to 20%.

PMD (registered in Australia as “extract of lemon eucalyptus”) is not an essential oil product but rather a chemical derived from the distillation of the lemon eucalyptus plant.

Botanical products generally contain one or more of the extracts of Eucalyptus, Citronella, Melaleuca, peppermint or Leptospermum. Botanical products have been shown to provide limited duration of protection.

Repellents do not kill mosquitoes; they prevent mosquito bites by inhibiting the mosquito’s stimuli for blood feeding. Some mosquitoes may be attracted to individuals wearing repellent but mosquitoes will not bite if an effective repellent is used and it has been applied appropriately.

Repellents should be reapplied as soon as any biting mosquitoes are noticed. The estimated reapplication times can be influenced by an individual’s activity, climatic conditions and local mosquito populations. However, over application of a repellent will not increase protection times. Mosquitoes can detect, and bite, areas where no repellent has been applied. Only a small quantity of repellent, applied evenly to exposed skin, is required for effective protection. Do not apply repellents underneath clothing.

Are insect repellents safe?

There is a perception that synthetic repellents such as DEET or picaridin can be toxic to humans. However, despite the widespread use of such products internationally, very few cases of adverse reactions have ever been documented. Serious adverse reactions generally result from gross misuse of repellents such as ingestion, ocular exposure or excessive application particularly on young children. It should be remembered that botanical based products also have the potential to cause skin irritation.

Other methods of personal protection

Electronic vaporiser units release insecticides (e.g. synthetic pyrethroids) from slow-release mats or liquids and can be very effective indoors or in sheltered outdoor areas

Mosquito coils containing insecticides (e.g. synthetic pyrethroids) can be effective in sheltered outdoor areas but are generally not recommended for indoor areas. Coils containing only botanical products (e.g. citronella) offer less protection.

Insecticides (e.g. synthetic pyrethroids) in the form of knockdown aerosols or residual surface sprays may assist in providing protection indoors. The application of insecticides onto the outside of buildings and/or terrestrial vegetation as “barrier treatment” has been shown to provide some protection for the homeowner. Electronic devices that purport to repel mosquitoes with sound (e.g. ultrasonic devices) have repeatedly been shown to be ineffective and should not be used. Commercial mosquito traps vary greatly in their efficacy. There is no evidence that the operation of these traps around the home or garden will prevent mosquito bites. Traps that primarily use UV light will not generally collect many mosquitoes but rather large numbers of non-biting insects.


Treatment of mosquito bites

The classic “mozzie bite” is an itching, inflamed lump on the skin and is an allergic reaction to the saliva injected by the mosquito during blood feeding.

The severity of the reaction is highly variable between individuals and may be determined by a person’s sensitivity as well as prior exposure to mosquito bites. Clean and dry the bite with warm soapy water and a clean cloth. Application of a cool compress (i.e. icepack wrapped in cloth) can reduce inflammation.

The application of a medication lotion (e.g. anti-inflammatory, anti-puritic) or soothing substance (e.g. aloe vera) may reduce itchiness and the use of an antiseptic cream will prevent secondary infection. If secondary infection occurs, consult a medical professional for specific advice. Severe reactions may need to be treated with topical or oral antihistamines but consult a medical professional for specific advice.

Many home remedies exist for the treatment of mosquito bites. The application of a paste comprised of a mixture of baking/bi carb soda and water is thought to offer some relief from itching but there are no scientific studies to support this treatment. Care should be taken if applying essential oils (e.g. lavender or eucalyptus) directly to the skin as these products may result in secondary skin irritation.

 

The following information is sourced from "The Conversation". The Conversation is a collaboration between editors and academics to provide informed news analysis and commentary that’s free to read and republish.

Why do mosquitoes suck?

Only female mosquitoes bite. Blood provides a perfect nutritional boost for egg development but who or what mosquitoes bite varies with species. Many mosquitoes opportunistically bite whatever warm blooded creature is about. That includes people. Some people more than others.

Mosquitoes aren’t “dirty syringes”. They don’t pass on pathogens through infected droplets of blood. When mosquitoes insert their mouthparts into our skin, it’s not like they’re sticking in a drinking straw. There are some tubes that suck and some tubes that spit. The spit they inject contains a mix of chemicals, some help get the blood flowing and some make their bite a little less noticeable. Unfortunately, that spit may also contain virus.

If a mosquito sucks up a virus-filled blood meal, that virus must then escape the gut and spread throughout the body of the mosquito until the salivary glands are infected. This process can take from a few days to over a week. But time isn’t all that matters. There is no malicious intent in mosquitoes transmitting viruses. The viruses are simply taking advantage of the mosquitoes’ evolutionary initiative to exploit vertebrate blood.

The viruses don’t make the mosquito sick, that wouldn’t make sense as the virus wants to make sure it makes it to the next host. Unfortunately, humans can fall ill following the injection of a mouthful of virus filled mozzie spit.

Why mosquitoes seem to bite some people more

There are hundreds of mosquito species and they all have slightly different preferences when it comes to what or who they bite. But only females bite; they need a nutritional hit to develop eggs.

Finding someone to bite

Mosquitoes are stimulated by a number of factors when seeking out a blood meal. Initially, they’re attracted by the carbon dioxide we exhale. Body heat is probably important too, but once the mosquito gets closer, she will respond to the smell of a potential blood source’s skin.

Studies have suggested blood type (particularly type O), pregnancy and beer drinking all make you marginally more attractive to mosquitoes. But most of this research uses only one mosquito species. Switch to another species and the results are likely to be different.

There are up to 400 chemical compounds on human skin that could play a role in attracting (and perhaps repulsing) mosquitoes. This smelly mix, produced by bacteria living on our skin and exuded in sweat, varies from person to person and is likely to explain why there is substantial variation in how many mozzies we attract. Genetics probably plays the biggest role in this, but a little of it may be down to diet or physiology.

One of the best studied substances contained in sweat is lactic acid. Research shows it’s a key mosquito attractant, particularly for human-biting species such as Aedes aegypti. This should act as fair warning against exercising close to wetlands; a hot and sweaty body is probably the “pick of the bunch” for a hungry mosquito! Probably the most famous study about their biting habits demonstrated that the mosquitoes that spread malaria (Anopheles gambiae) are attracted to Limburger cheese. The bacteria that gives this cheese its distinctive aroma is closely related to germs living between our toes. That explains why these mosquitoes are attracted to smelly feet. But when another mosquito (such as Aedes aegypti) is exposed to the same cheese, the phenomenon is not repeated. This difference between mosquitoes highlights the difficulty of studying their biting behaviours. Even pathogens such as malaria may make us more attractive to mosquitoes once we’re infected. 

Only females bite because they need a nutritional hit to develop eggs. Sean McCann/Flickr, CC BY-NC-SA Researchers are trying to unscramble the irresistible smelly cocktails on the skins of “mosquito magnets”. But the bad news is that if you’re one of these people, there isn’t much you can do about it other than wearing insect repellents.

The good news is that you may one day help isolate a substance, or mixes of substances, that will help them find the perfect lure to use in mosquito traps. We could all then possibly say goodbye to topical insect repellents altogether.

Attraction or reaction?

Sometimes, it’s not the bite as much as the reaction that raises concerns. Think of the last time the mosquito magnets in your circle of friends started complaining about being bitten after the event where the purported mosquito feast took place. At least, they appear to have attracted more than the “bite free” people who were also at the picnic, or concert or whatever.

But just because some people didn’t react to mosquito bites, doesn’t mean they weren’t bitten. Just as we do with a range of environmental, chemical or food allergens, we all differ in our reaction to the saliva mosquitoes spit while feeding.

People who don’t react badly to mosquito bites may think they haven’t been bitten when they’ve actually been bitten as much as their itchy friends. In fact, while some people attract more mosquito bites than others, there’s unlikely to be anyone who never, ever, gets bitten.

The problem is that people who don’t react to mosquito bites may all too easily become complacent. If you’re one of them, remember that it only takes one bite to contract a mosquito-borne disease.

Finally, there is no evidence from anywhere in the world that there is something you can eat or drink that will stop you being bitten by mosquitoes. No, not even eating garlic, or swallowing vitamin B supplements. Perhaps if we spent as much time thinking about how to choose and use mosquito repellents as we do about why mosquitoes bite our friends and family less than us, there’d be fewer bites all around.



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