Travel health: Keeping Up-to-Date With The Risks of Insect-Borne Disease

Anna Sayburn

Disclosures

June 25, 2019

When people think of travel health, they tend to think about vaccinations and perhaps malaria chemoprophylaxis. But with insect-borne disease such as Zika and West Nile Virus gaining in profile, what other precautions should GPs be advising?

Changing Profile of Travel 

The numbers of people travelling overseas continues to increase year-on-year, and has done so since the financial crisis of 2008, says Dr Dipti Patel, clinical director at the UK's National Travel Health Network and Centre (NaTHNaC).

"Every year since [2008] the number of UK travellers abroad has increased. Last year it was in the region of 72 million," she says. That means almost as many people travel overseas from the UK as from the whole of the US, she points out. "We are a nation of travellers.

"The most popular destinations for us are mainland Europe; so France and Spain are really popular, and also the USA. But there is an increase in people going to more tropical destinations."

Dr George Kassianos, GP and president of the British Global & Travel Health Association, agrees. "UK residents not only travel for pleasure to many countries around the globe but also they visit friends and relatives, which increases their risk of contracting infectious disease as they usually live with locals."

Dr Patel says that these 'VFRs' (visiting friends and relatives) are one of the fastest-growing groups of travellers. "They may be people who were born abroad and have emigrated to the UK, or whose family emigrated to the UK. We have a big VFR population going to West Africa, we have a big population for Pakistan, South Asia, India."

One issue, she says, is that people may not realise they are at risk, because they have lived or travelled in these countries before, so may not take precautions that leisure travellers would take.

Emerging Insect-Borne Diseases 

Most travellers are aware of the risk of malaria and yellow fever, and the need to have chemoprophylaxis or vaccination. But for many insect-borne diseases, such as dengue fever, West Nile Virus and Zika virus, the only protection is to avoid being bitten.

"Everyone focuses on vaccine-preventable stuff and malaria which of course are really important, but [they] tend to forget other things in terms of infectious diseases. There is a number of infectious disease hazards which are spread by insects and ticks that there aren't any preventive measures for other than bite prevention," says Dr Patel.

"Malaria chemoprophylaxis is extremely important but it cannot be on its own," says Dr Kassianos. "Travellers should also take every measure to avoid mosquito bites, particularly during the night when it comes to malaria. Yellow fever is a severe and life-threatening infection. The yellow fever vaccine is very effective and mosquito bite avoidance at day-time is also very important."

Zika virus has been in the news because of outbreaks of microencephaly linked to the disease in children born in central and south America.

"For Zika virus endemic areas there is a specific advice for couples wanting to fall pregnant. Women should avoid becoming pregnant for 2 months after their last possible exposure to Zika virus. If both partners travelled, then 3 months will apply," says Dr Kassianos. Use of barrier contraceptives is also recommended.

And it isn't just tropical destinations where travellers are at risk of insect-borne disease. There have been local outbreaks of Zika virus in Florida, dengue virus in Portugal and malaria in Greece. This can come about, says Dr Patel, when vectors such as mosquitos or ticks in the home country become infected with the virus, perhaps by biting a returning traveller from a country where the disease is endemic.

"If the vector exists, there is the potential for importation. Fortunately, we have good surveillance systems [in Europe] so they can pick up the issue very quickly and be able to take measures," she says.

But insect-borne diseases in Europe are not necessarily exotic imports. Tick-borne encephalitis is a real problem in some parts of Europe and may not be considered by UK travellers.

"You might have people doing trekking or hiking holidays in forested areas of Germany, and they might not be thinking of tick-borne encephalitis but it is a real risk in that part of the world," says Dr Patel.

There is a vaccine for tick-borne encephalitis, says Dr Kassianos, which can be considered "as an additional measure" on top of bite avoidance.

Bite Prevention Advice 

So what should GPs advise? The first step, says Dr Patel, is to avoid areas where mosquitos or ticks are known to be present, particularly at the time of day when they are most active. Different types of mosquito are active at different times of day.

Appropriate clothing – such as long trousers tucked into socks in grassland where ticks are present – is also important. "There are certainly prevention measures you can take in terms of how you dress, wearing appropriate clothing, making sure you cover up properly," says Dr Patel.

The next step is insect repellent. "We recommend Deet 50%, applied twice daily," says Dr Kassianos. Both doctors agree that this is the best option for everyone, including pregnant women and children over the age of 2 months.

Different concentrations give different hours of protection, says Dr Patel. She says there is no evidence for opting for concentrations above 50%.

"If people don't like using Deet there are alternatives but they don't last as long. Icaridin or picaridin, preparations like PMD. Deet is really the best one," she adds.

She warns that GPs should be alert for people planning to "protect" themselves through some of the wilder recommendations to be found on the internet.

"There's a lot of myths out there about things that people can use to repel insects, like eating garlic and taking vitamin B12, but these are not evidence based and we would not advocate that at all," she says.

Remaining Alert

It's hard to tell whether UK cases of insect-borne disease are increasing, says Dr Patel, because symptoms can be minor in some cases, so people will not report them. "People don't get diagnosed – they may have a flu-like illness and not realise that they've had something like dengue," she says.

However, Public Health England do see a spike in cases when there have been outbreaks of disease in a particular country, she says. "In 2014, 2015 there was a real increase in the numbers of cases of Chikungunya being reported among people travelling back from the Caribbean and there was a big outbreak going on at the time."

All this can add to the difficulties for GPs trying to make diagnoses for people with symptoms of infectious disease, who may not remember to mention their travel history.

"Health care professionals might not think to ask but regardless I think if someone comes to you with the symptoms of an infectious disease you should be asking if they've travelled, including in Europe," says Dr Patel.

The best way to stay up-to-date about current travel health recommendations is through websites such as TravelHealthPro, provided by NaTHNaC on behalf of Public Health England.

Charitable organisations such as the British Global and Travel Health Association also provide training and education in travel health.

Resources:

TravelHealthPro – up-to-date country-specific information about travel health risks, recommendations and alerts.

British Global and Travel Health Association – research and education into travel health, for healthcare professionals.

TravelHealthPro factsheet on avoiding insect and tick bites.

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