Each year around the world, mosquitoes are responsible for over one million deaths. They cause more suffering than any other organism thanks to their impressive ability to act as a vector for a huge range of diseases.
Female mosquitoes require protein from blood to reproduce, which is why they feed so feverently.
To get the most up-to-date information on the current risks to travellers posed by mosquitoes, as well as some top tips to prevent sickness while overseas, I contacted Dr Stuart Rose at the Travel Medicine Center of Western Massachusetts.
COMMON DISEASES SPREAD BY MOSQUITOES
The malaria parasite, known as plasmodium, mainly exists in tropical and sub-tropical areas. The annual number of reported cases is around 200 million, with roughly one in four leading to death – largely in African children who have no access to treatment. Patients typically present with fever, shaking chills or flu-like symptoms. Different species of Anopheles mosquitoes spread the disease, so long-term travellers need to make sure they take the appropriate antimalarial drugs.
Dr Rose explains that ‘One function of a travel clinic is to review maps of where malaria occurs in each country and then check the traveller’s exact itinerary’. He adds that no precautions are required in high altitude areas, because mosquitoes favour higher temperatures.
This mouthful phrase is an umbrella term for a group of related viral agents that cause inflammation of the brain, otherwise known as encephalitis. The most common of these that affect humans are Japanese encephalitis and West Nile virus.
Japanese encephalitis is present in Asia and the western Pacific, and your risk of catching it depends on specific location and the duration of your stay. ‘Travellers to Asia may need to be vaccinated against Japanese encephalitis if they will be in endemic areas for more than one month,’ explains Dr Rose. However, he adds that, fortunately, ‘only one in one hundred exposures results in brain damage’.
There’s no vaccination available for West Nile virus, but most affected people don’t experience symptoms. About one in five will develop a fever and fewer than 1% develop serious – sometimes fatal – neurological illness. West Nile virus is now native to the USA and epidemics peak in mid-August. In the past, it has posed a greater risk in Texas, Mississippi, Louisiana and South Dakota, but, Dr Rose says, ‘domestic travellers can be variably exposed depending on their destination and the annual geographic distribution of the outbreaks.’
RIFT VALLEY FEVER
Although Rift Valley fever is most commonly seen in domesticated animals, it can affect humans too. The disease is almost exclusively reported in Africa – especially eastern and southern regions. Most human cases are mild, but in some, the retina becomes inflamed, leading to loss of vision.
Dengue is the world’s most common arboviral disease. While there are almost 400 million infections, and over 100 million reported cases annually, only a small proportion lead to severe symptoms, and roughly one in every 2000 cases leads to death. Clinical care is key in the recovery of the most severe cases. The highest risk is in infants whose mothers are ill towards the final stages of their pregnancy and during delivery. It’s most prevalent in Latin America, the Caribbean and Southeast Asia, but occurs in over 100 countries. There’s no vaccine. Infected patients should stay hydrated and rest up, while the worst cases may require intensive care.
The highest-risk areas for yellow fever virus are sub-Saharan Africa and tropical South America. Travellers attempting to enter another country after visiting a known risk area will usually have to produce evidence that they have been vaccinated against it.
ITCHES, ALLERGIES AND INFECTION
Even if you don’t catch any diseases from mosquito bites, there are still complications to look out for. Mosquitoes use a proboscis to pierce the skin and suck out the blood. Their saliva contains substances that stop the blood from clotting and prevent inflammation, but many people develop allergic responses to these substances, causing itching and irritation. A common reaction is to scratch, which can lead to infection. Some bacteria will cause large and painful open wounds if not treated with a course of antibiotics.
Prevention begins with awareness. ‘First, know the risks’, says Dr Rose. ‘When and where are the mosquitoes biting?’ The following precautions can also significantly reduce your chances of being bitten or contracting a mosquito-borne disease.
💉 Seek medical advice on vaccinations from a travel clinic before your trip. Vaccinations are sometimes pricey, but the cost of not receiving them could be far greater.
💊 Take antimalarial tablets in at-risk areas, and follow the instructions for their use carefully.
💉 Stay in accommodation with screened windows, air conditioning and bed nets, and give your room a spray with insecticides.
💊 Use insect repellent containing at least 30% DEET. ‘These can last 8-12 hours, depending on the brand.,’ Dr Rose says. ‘Ultrathon Lotion was rated #1 by Consumers Reports and lasts 12 hours. Picaridin is a non-DEET alternative.’
💉 Cover your arms and legs with protective clothing treated with permethrin, especially when mosquitoes are most active in the early morning and late afternoon. ‘The combination of DEET skin repellent and permethrin-treated clothing gives 99% protection,’ says Dr Rose.
💊 As mosquitoes lay their eggs in freestanding water, clean or cover any water supplies close to your accommodation, and avoid, or take extra precautions around, areas like rice paddies.
💉 Use anti-itch creams and tiger balm to prevent you from scratching and to lessen the chances of infection.
💊 If you start to feel unwell while overseas, seek medical advice as soon as possible.
LATEST TRENDS AND ADVICE
While a traveller’s health is often the deciding factor when it comes to choosing a travel destination, Dr Rose says ‘choice of destination is often more related to political instability than disease. However, he recommends that people consider all risks, whether they be from unrest, disease or natural disasters.
In the opening chapter of his book International Travel Health Guide, which is available on his travel medicine products and information website, Dr Rose explains that often, people tend to overexaggerate the risks from dangers such as terrorism or exotic diseases like Ebola virus, and ‘disregard or minimise the more common perils of motor vehicle accidents and malaria’.
‘Large disasters often divert attention from the simple day-to-day precautions that you can take to stay healthy and safe,’ he writes.
INTERESTING FACTS (also from Dr Rose’s book)
* There is a 60 to 70% possibility of illness when traveling in less developed countries for up to 90 days (median trip duration: 19 days). Most of these illnesses are minor
* There is a 5 to 8% chance you will seek medical care while traveling in a developing country
* Your chance of being hospitalised is less than 1%
* The most common reported illnesses are: diarrhea (34%); a respiratory disease (26%); a skin disorder (8%); acute mountain sickness (6%); motion sickness (5%); an accident and injury (5%); and an illness with fever (3%)
* On return home, there is about a 25% chance that you will have a bout of diarrhea, a respiratory illness, a skin problem, or a fever related to your trip
The main variables that affect your chances of getting sick are:
1) Duration of trip
2) Whether or not you use antimalarial drugs
3) Whether or not you take measures to prevent insect bites
4) Your vaccination status
5) Your risk-taking (or avoidance) behaviour
6) Your underlying health status
So, the most important take-home messages are to visit a travel clinic before departure, to learn about the risk for the region you’re visiting, to have the required vaccinations and take the relevant drugs, and to take precautions against being bitten by mosquitoes. They may be a traveller’s worst nightmare, but if you’re sensible they needn’t ruin your travels.