Small But Deadly: Tiny Vectors That Pose a Major Threat

Written by Jose Muñoz and Natalia Rodríguez (ISGlobal)

The real problems are caused by much smaller animals: arthropods As specialists working in the field of tropical medicine, we see some very strange medical cases in our practice, including patients who have been attacked by wild animals. In the imagination of certain travellers, the animals that inspire the greatest terror are crocodiles, snakes and even lions. However, unless they think that it is a good idea to kneel down in front of a sleeping crocodile to take a photograph (that actually happened), those animals rarely present a risk to travellers.

The injuries caused by wild animals we see most often in the Tropical Medicine Department in Barcelona's Hospital Clínic are monkey bites (30 to 50 every year) and many of these are the result of rash behaviour on the part of the traveller. However, the real problems are caused by much smaller animals, some so tiny that they are true masters in the art of being invisible: arthropods.

In a new infographic series entitled “The Usual Suspects”, ISGlobal has profiled six of the most dangerous of these aggressive repeat offenders Arthropods belong to the phylum Arthropoda, the most diverse and numerous division in the animal kingdom. This division includes many of the culprits found on our list of “usual suspects”, including mosquitoes, sandflies, fleas and bedbugs. For starters, these arthropods are among the most common causes of consultations for skin lesions following a trip to a tropical or subtropical country. Examples include bites that have become infected because of the humid environment and unhygienic conditions during the trip; allergic reactions to the toxins injected by the bites; parasitic infestation under the skin caused by fly larvae (myiasis caused by Cordylobia anthropophaga in Africa and by Dermatobia hominis in Latin America); and parasitic infestation of the foot by "tunga penetrans", tiny sand fleas measuring less than a millimetre across.

Some of them transmit common, life-threatening diseases, such as malaria Some of these “small but deadly” arthropods transmit common, life-threatening diseases, such as malaria, yellow fever and Chagas disease, some of which pose a considerable threat to public health in our countries (dengue, chikungunya and the new menace Zika virus). In a new infographic series entitled “The Usual Suspects”, ISGlobal has profiled six of the most dangerous of these aggressive repeat offenders.

At the top of our most wanted list is the Anopheles mosquito. Females of this genus transmit malaria in many countries throughout Africa, Asia and Latin America. Malaria—and especially the type caused by the most common and deadly malaria parasite, Plasmodium falciparum—can be fatal if not properly treated. About 500 cases are registered every year in Spain, and malaria is one of the most well known diseases among the travellers we see.

To avoid the bites: insect repellent, long-sleeved clothing and mosquito nets Another of the usual suspects—renowned because of its ability to transmit viruses like yellow fever, dengue, chikungunya and Zika—is the Aedes mosquito. Both Aedes aegypti and Aedes albopictus (the famous tiger mosquito now found in most parts of the Mediterranean region) transmit a variety of viruses. As well as their potential for causing severe disease in travellers, there is now a real threat that these viral diseases will become endemic in the areas where the mosquito vector is now present, including Spain, Italy and France.

To avoid the bites of these tiny malefactors and to reduce your risk of getting an infectious disease, we recommend applying insect repellent to all exposed parts of the body, using a product specifically approved for use in tropical regions and following the instructions on the package insert. We also recommend wearing long-sleeved clothing covering most of the body and choosing light colours (some mosquitoes are attracted to dark colours). The use of mosquito nets or, when nets are not available, sleeping in a closed, air-conditioned room, helps to safeguard you from infections, like malaria, which are transmitted by mosquitoes that are more active at night. Some mosquitoes are more active during the day—the tiger mosquito, for example—and others are more active during the evening and at night, such as the Anopheles mosquito, which transmits malaria.

Other less well known arthropods that also deserve a place on the list of usual suspects: ticks and the kissing bugThere are also other, less well known, arthropods that can cause common infectious diseases in travellers, which also deserve a place on the list of usual suspects. A good example are ticks, which are considered to be excellent transmitters of an long list of infectious diseases. The one most often found in travellers to tropical and subtropical areas is African tick bite fever caused by the bacterium Rickettsia africae and transmitted by a tiny coloured tick of the genus Amblyomma. This infection is very common in people who visit natural parks in Central and Southern Africa (according to some studies, it is the cause of 25% of the fevers affecting people who come from these areas). If you look carefully, these ticks can often be espied in the brush or weeds, inside tents and even in vehicles. We recommend that all travellers, especially those who have visited natural parks or have been walking or hiking, check their skin carefully when showering after a visit to a park in sub-Saharan Africa to remove ticks as soon as possible.

Don’t bother the big ones and take care not to come into contact with the tiny onesOne of the most monstrous of all the arthropods is the triatomine bug. This bug measuring almost 2 cm in length, also known as the kissing bug or vinchuca, transmits Chagas disease in most Latin American countries by inoculating the host with a parasite it carries in its faeces. Although exceptional in travellers, Chagas disease, which can cause serious heart problems including arrhythmias and heart failure, is common in the Latin American population, both among people who remain in their country of origin and emigrants.

So you see, despite their diminutive size, some arthropods are real serial killers. So whether you are planning to travel abroad or not, a good piece of general advice about animals would be “Don’t bother the big ones and take care not to come into contact with the tiny ones.”

Jose Muñoz is Head of Tropical Medicine and International Health at the Hospital Clínic de Barcelona and a researcher at the Barcelona Institute for Global Health (ISGlobal).

Natalia Rodríguez is a specialist who works in the Tropical Medicine and International Health Department at the Hospital Clínic de Barcelona and a researcher at the Barcelona Institute for Global Health (ISGlobal).

More Information

Infographic series "Usual Suspects: 6 tiny vectors that represent a huge threat to our health"

• 001 Anopheles mosquito
• 002 Aedes mosquito
• 003 Vinchuca
• 004 Phlebotomine fly
• 005 Ticks
• 006 Culex mosquito
• 007 Summary