Malaria is caused by Plasmodium parasites, carried by female Anopheles mosquitoes that bite between dusk and dawn. It is preventable, it is treatable, and it kills people every year in the UK — almost always because it was not prevented and then not diagnosed quickly enough.
Several hundred cases are confirmed in the UK annually, every one of them acquired abroad. The pattern they form is the most useful thing to know about the subject, and it is not the pattern most writing on it assumes.
Who actually gets it
Of UK cases in a recent year, around three-quarters were in people visiting friends and relatives, not holidaymakers. Around a fifth were tourists and a small remainder business travellers. Roughly seven in ten of those with a known destination had been to West Africa.
And where it was known whether antimalarial tablets had been taken, around nine in ten of the people who caught malaria had not taken them.
That reframes the whole subject. The highest-risk traveller from the UK is not someone off on safari but someone going back to the country they or their parents came from, to stay with family, for several weeks, in an ordinary house rather than an air-conditioned hotel — and doing so without tablets, because malaria was a normal fact of childhood there and did not seem like something to buy medicine for.
The reason that reasoning fails is waning immunity. Partial immunity acquired by growing up in an endemic area fades within a year or two of leaving and does not come back. Someone who has lived in the UK for a decade is, for practical purposes, as susceptible as anyone else. Children born here have no immunity at all, and young children are at the highest risk of dying from it.
Pregnancy also raises the risk substantially, for both mother and baby.
What it does
The parasite enters the blood with the mosquito's bite, travels to the liver, multiplies there, and then infects and destroys red blood cells in cycles. The illness that results is not subtle: fever, often coming in waves, with chills, sweats, headache, aching, vomiting and diarrhoea. It is very commonly mistaken for flu or a stomach upset, which is precisely the problem.
Plasmodium falciparum, the dominant species in sub-Saharan Africa, is a medical emergency. It can progress within a day or two from a flu-like illness to organ failure, coma and death, and most UK deaths from malaria are from this species in someone who waited to see whether they felt better. Symptoms usually appear within a few months of exposure and most often within a month.
Plasmodium vivax and P. ovale are less immediately dangerous but can lie dormant in the liver and relapse months or even years later, including after prophylaxis has finished.
One thing older writing on this subject gets wrong and worth correcting: a traveller returning to the UK does not become a public health risk to others. Malaria needs a competent Anopheles mosquito to complete its cycle, and onward transmission within the UK does not practically occur. The reason to take this seriously is personal, not civic.
The four steps
UK guidance organises prevention as awareness, bite avoidance, chemoprophylaxis and diagnosis. All four matter, and the last two are the ones people skip.
Awareness
Risk varies not just by country but by region, altitude, season and sometimes by individual town, and the recommendations change from year to year as resistance patterns shift. There is no way to know the current advice for a destination except to look it up, and the UK's national travel health services publish country-by-country guidance for exactly this.
Pre-travel advice is best sought four to six weeks before departure, which allows time for vaccines and for one antimalarial that has to be started weeks ahead. Last-minute advice is still worth getting — something useful can be done the day before a flight.
A pharmacy, a GP practice offering travel services, or a travel clinic can all advise. Antimalarial tablets are generally not available on an NHS prescription and are bought, either over the pharmacy counter or on a private prescription.
Bite avoidance
The mosquitoes that carry malaria bite from dusk to dawn, so this is mainly about the evening and the night.
- Repellent containing 50 per cent DEET on exposed skin, reapplied as directed. Fifty per cent is the recommended strength; higher concentrations do not extend protection, so "as much as possible" is not the goal. DEET is safe in pregnancy and in children over two months at this strength.
- Apply DEET after sunscreen, not before — and use a sunscreen of SPF 30 to 50, because DEET reduces the protection a sunscreen gives. Sunscreen is not needed after dusk, which is when repellent matters most.
- An insecticide-treated bed net, tucked in, for any room that is not screened and air-conditioned. This is one of the most effective measures there is.
- Cover up after dark — long sleeves, long trousers, socks. Uncomfortable in the heat, and the mosquitoes are biting in the cool of the evening anyway.
- Air conditioning and screened windows reduce risk considerably where available.
- Plug-in insecticide vaporisers and knockdown sprays for the bedroom are worth using.
Repellents based on citronella and other plant oils are widely sold and are not an adequate substitute in a malarious area. They work for a much shorter time than DEET and are not what national guidance recommends where the mosquito can kill. This is one place where preferring a herbal product to a chemical one carries a real cost.
Chemoprophylaxis
Tablets reduce the risk of malaria by more than ninety per cent when taken correctly. They do not eliminate it, and that residual risk is the reason the fourth step exists.
Which one is right depends on the destination's resistance pattern, on the length of the trip, and on the traveller's own health and other medicines — it is a decision to be made with a pharmacist or clinician rather than chosen from a page. The usual options:
- Atovaquone with proguanil — started one to two days before entering the area, and continued for seven days after leaving. The short tail makes it popular for short trips.
- Doxycycline — started one to two days before, continued for four weeks after leaving. Also offers some protection against other infections, and causes sun sensitivity.
- Mefloquine — started two to three weeks before travel, deliberately, so that tolerance can be assessed before departure, and continued for four weeks after. Taken weekly.
- Chloroquine with proguanil appears in older writing and is no longer available in the UK, the combination products having been discontinued.
Two things about this routinely go wrong.
The first is the mechanism. Prophylaxis does not build immunity, as older writing on this subject claimed. The tablets suppress the parasite; starting before departure establishes the drug in the body and, for mefloquine, allows side effects to show up at home rather than abroad.
The second is finishing the course, which is the commonest failure of all. The parasite is in the liver during the trip and emerges into the blood afterwards, which is exactly what the post-travel tablets are for. Stopping on the flight home, or a week into a four-week tail because the holiday is over and the tablets are a nuisance, removes most of the protection paid for.
Antimalarials should not be bought at the destination. Counterfeit and substandard antimalarials are a documented and serious problem in several of the countries where they are most needed.
Diagnosis
This is the part that saves lives, and it is one sentence.
Any fever or flu-like illness after visiting a malaria area needs same-day medical attention, and the travel has to be mentioned.
Not next week, not after a few days of paracetamol to see how it goes. Suspected malaria is a medical emergency, a blood test gives an answer within hours, and treatment started early almost always works while treatment started late sometimes does not.
Three things to add to that:
- Having taken the tablets does not rule it out. No regimen is completely effective, and people who took their prophylaxis properly still occasionally get malaria.
- The window is up to a year, and longer for the relapsing species. A fever four months after a trip still warrants mentioning the trip.
- Say where and when, unprompted. A clinician who does not know about the travel will reasonably investigate a fever as something ordinary, and this is the single commonest reason malaria is diagnosed late in the UK.
Out of hours, that means 111 or an emergency department rather than waiting for a GP appointment.
Pregnancy and children
Both need specific advice rather than general advice. Falciparum malaria in pregnancy is considerably more dangerous, for mother and baby, and travel to a high-risk area while pregnant is worth questioning rather than simply preparing for. Several antimalarials are unsuitable in pregnancy and while breastfeeding, and the choice narrows accordingly.
Children need weight-based dosing, and the youngest are at the highest risk of severe disease. Bite avoidance matters most of all for them: a treated net over the cot, repellent at the right strength for their age, and covering up after dark.
Before travelling
- Look up the current advice for the specific regions being visited, not just the country.
- Get pre-travel advice four to six weeks ahead where possible, and at any point if that has passed.
- Mention all existing conditions and medicines, which affect which antimalarial is suitable.
- Buy repellent, a treated net if needed, and the full course of tablets including the post-travel tail, before leaving.
- Check that travel insurance covers the destination and any planned activities.
- For anyone visiting family in a country they came from: take the tablets. Childhood immunity has gone, and it is the single clearest finding in the UK figures.