Table 1 Repellents - personal observations and notes

To understand the context of research on tourists’ (n = 373) use of personal protection from insect bites, I accompanied as paying client one group each of the two participating operators (Group 1: 7 clients, all-camping, 7 days/6 nights; Group 2: 9 clients, camping/lodge, 9 days/8 nights) on trips to Manu National Park in the Peruvian Amazon. I observed their protective measures throughout the day and on night excursions, and at various distances from potential insect breeding and resting sites or areas of congregation, such as insect clouds hovering a few centimetres above the river to await the emerging swimmer.

Both operators had briefed their clients thoroughly prior to the trip and emphasised the need for protection from insects. Therefore, it came as no surprise that all of them had brought plenty of repellent from home, and that some used it often and generously. The DEET content varied considerably; some were slow-release preparations. However, everybody got bitten, some very badly with multiple angry red lumps. Toilet-breaks revealed a previously neglected area of application: women’s buttocks. Tourists commented ‘I had zillions of bites’, ‘undeterred by DEET’, ‘attacked very badly’.

Believing that people might be less compliant than assumed led to me demonstrate to myself and others that consequent, correct and frequent use of repellent does prevent bites. During the two weeks in the jungle, I used a variety of repellents, lotions, or sprays, many a commercial sample provided at travel medicine conferences, including repellents for military use, and appropriate clothing (often 2 layers). My efforts worked well during the first day while not quite yet in the rainforest. However, from day two, insects bit through repellent - at times even through freshly applied product. The identity of the biting insects (mosquito, sand fly, midges) could not be established but did not matter at the time; the nuisance was obvious, and any infected insects could not be identified anyway. For two days, one 100% DEET preparation was used, which only worked for 1 h rather than the suggested 10 h. In short, despite correct use, the repellents did not repel. Out of curiosity, I applied the juice of the traditionally used Huito fruit (Genipa americana L.) in two large patches on one arm. Once the skin adopted the typical dark-blue stain, lasting for several days, the patches remained bite-free.

Humidity, sweat, heat and abrasion will all have influenced the efficacy of the various repellents, and the observed sample was small. But this trip happened in real life! While some products may have performed beautifully in a laboratory, they did not protect people on location.

The outcome for those who used repellents was disappointing. Reasons of those who did not use repellents correctly were: thinking they can judge the situation and need for repellents, thinking there were no insects until too late, it was too humid and too hot, there was no water to wash hands, not knowing about potential diseases or that they would get them. Others forgot, could not be bothered, or sprays stung in eyes and nose, especially when applied in windy conditions or on boats on the river.

The use of personal insect repellents favoured us who had money and access to the products. Local tourism workers, such as boatmen or cooks, did not have repellents. Pathogen-carrying vectors do not distinguish between foreign tourists and local residents. We use repellents for a short time to protect us from diseases that affect millions of people in poorer countries. Cost, unavailability, or impracticality of use, make the advice to people in endemic regions quite pointless. Repellents are hardly a reliable way to lower the burden of global vector-borne diseases. What would do a better job?