Fever a Few Days After Mosquito Bites Abroad? Dengue, and the Warning Signs That Change Everything

Who gets it, and where

Dengue is the most common mosquito-borne viral illness in the world and, in CDC's words, endemic throughout the tropics and subtropics in more than 100 countries, with an estimated 390 million infections a year. Unlike malaria it is more of a risk in cities and residential areas than in the bush, because the mosquito that carries it, Aedes, lives indoors and out, in dark cool places such as closets, under beds and behind curtains, and bites mostly in the early morning and late afternoon. CDC's risk maps put the Caribbean, Central and South America, South and Southeast Asia and much of Africa in the frequent-risk category; the Dominican Republic and Egypt, two of the countries we write about, are on that list.

CDC notes that 40 to 80 percent of infections cause no symptoms at all, that risk rises with trip length and with local outbreaks, and that having had dengue before does not mean avoiding those destinations, only taking bite prevention seriously, because a second infection carries a higher risk of severe disease.

What it feels like, and the three phases

According to CDC, symptomatic dengue begins abruptly after an incubation of 5 to 7 days (range 3 to 10) and runs in three phases. The febrile phase: fever for 2 to 7 days, sometimes in two waves, with severe headache, pain behind the eyes, bone, joint or muscle pain, a blotchy rash, and sometimes minor bleeding such as nosebleeds, bleeding gums, bruising or small red spots on the skin. Some people have a flushed face or red throat in the first day or two. It is easy to mistake for flu, and in the first days a doctor cannot reliably tell the difference without a test.

The critical phase is the one to understand. CDC says it begins as the fever falls, around 38°C, and lasts 24 to 48 hours. Most people simply improve. A minority leak plasma from their blood vessels, and this is when severe dengue shows: the body compensates at first, so, in CDC's words, patients might appear well despite early signs of shock. Once blood pressure drops it drops fast. Then the recovery phase: fluid is reabsorbed, appetite returns, and a confluent rash with islands of white in a sea of red can appear and itch.

What you can do at home, and what not to take

CDC's management for dengue without warning signs is ambulatory: stay well hydrated, control fever with paracetamol (acetaminophen), and avoid medicines that affect clotting: aspirin, aspirin-containing products, and other non-steroidal anti-inflammatories such as ibuprofen. That last point is the one travellers get wrong, because ibuprofen is what most people reach for with aches and fever. CDC also asks people with dengue fever to keep avoiding mosquito bites so they do not seed the infection into the local mosquito population. For a child with a fever, NHS guidance is not to undress them or sponge them down to cool them.

There is no specific antiviral. For severe dengue the treatment is hospital fluids given carefully, and CDC is explicit that platelet transfusions as a precaution are not helpful and steroids are potentially harmful, which is worth knowing if either is offered abroad as a matter of routine.

Pregnancy

CDC's guidance is unambiguous: pregnant women with dengue should always be hospitalised. The chapter notes an association with miscarriage in the first trimester and with low birth weight and preterm birth, and that infection late in pregnancy can pass to the baby. If you are pregnant and have a fever in a dengue area, CDC's guidance points to prompt medical assessment, and to hospital if dengue is likely.

Preventing it

• Accommodation with well-screened windows and doors, or air conditioning. CDC notes Aedes aegypti lives indoors and outdoors and hides in dark, cool places in the room.
• Long sleeves and trousers, especially in the early morning and late afternoon, when CDC says the risk of Aedes bites is greatest. TravelHealthPro notes they feed from dawn to dusk and can bite at night in well-lit areas, so do not treat the rest of the day as safe.
• An effective insect repellent (CDC specifies EPA-registered products).
• Vaccine advice depends on where you are advised. CDC recommends no dengue vaccine for US travellers. In the UK, Qdenga is licensed from age 4, and JCVI advises it can be considered for travellers who have had dengue before; ask a travel clinic before you go.

You are already there: what this means in practice

Everything above is the CDC chapter. This section is ours. The practical reality for a traveller is that a dengue fever and a bad flu look alike for the first few days, that the thing which decides how the week goes is whether the warning signs appear as the fever drops, and that the single most common mistake is treating the aches with ibuprofen. So: paracetamol only, drink, rest, and from the day the fever starts to fall, watch for the warning signs above for 48 hours. In the Dominican Republic dengue risk is classed as frequent by CDC and resort doctors are the usual route when you need to be seen; in Egypt, too, CDC lists the country in its frequent-risk category. Our country guides cover the emergency numbers and what FCDO says about local care.

One more practical point from the chapter: dengue is a notifiable disease in many countries and testing is most useful in the first week of illness. If you are tested abroad, keep the result; and if you develop a fever within two weeks of getting home, tell the doctor where you have been, because CDC says dengue is usually missed unless the travel history is volunteered.

What a video doctor can and cannot do about this

A video consultation is one option in the first days: a doctor can take the history (where you have been, when the bites were, how the fever started), look at you and at the rash, weigh dengue against the other things that cause fever in travellers, including chikungunya and Zika, which the same mosquitoes carry, and malaria, tell you plainly what to take and what not to take, and go through the warning signs with you so you know exactly what you are watching for and when. For most people that is the whole of the useful answer, and it is a better answer than guessing in a hotel room.

What a video doctor cannot do is test you, give fluids, or watch your blood pressure through the critical phase. If warning signs appear, if you are pregnant, or if the doctor judges that this is dengue with any risk feature, CDC's guidance is hospital care, and a doctor would be expected to say so plainly.