What are Sand Flies and What Do They Look Like?

Sand flies are insects with a large number of hairs on their bodies, making them look fuzzy [1]. They have long legs, they are hunchbacked, and their wings are spear-shaped and always arched. These characteristics can be very difficult to see, since we are talking about a very small animal, measuring around 3 mm in length—smaller than the tip of your pencil! Sand flies are found on almost all continents, except Oceania.

Interestingly, sand flies cannot fly over long distances. Instead, they prefer to move around by making small hops. Sand flies are nocturnal, which means they are most active at night. Nighttime is when they carry out most of their activities, such as feeding and reproducing. Take a look at Figure 1 to see where and how sand flies develop.

Sand flies have short, rigid mouthparts. Both males and females feed on sugary plant substances such as nectar and sap. However, females also feed on blood, as they need more energy to produce eggs. The sand fly bite can be painful and sometimes a small pool of blood forms at the site. And worse, you would not believe how much it itches! The female can feed on the blood of various animals, including humans, and this is why sand flies are dangerous—at the time of the bite, the female can transmit disease-causing pathogens, mainly a type of parasite called Leishmania, which is a protozoan (Figure 1).

Leishmania and Sand Flies: A Dangerous Match

Did you know that more than a thousand species of sand flies have been identified around the world? Of these, only ~100 have an important impact on human and animal health. This is because not all sand fly species can carry and transmit all parasite species, there must be a “match” [2]. Once Leishmania successfully multiplies within a sand fly, that fly can transmit that specific parasite to its next host during a bite.

Leishmania can be transmitted between animals and humans. It has been found in up to 70 different species of animals and is a major health problem in ~100 countries around the world. The disease Leishmania parasites cause is called leishmaniasis, and this disease kills the most people in the world after Malaria, so it is super serious.

What is it Like to Have Leishmaniasis?

It is HORRIBLE to have leishmaniasis! This disease can show up in different ways, depending on factors such as the host’s immunity and the species of the parasite. Once Leishmania invades a person, it can attack vital organs leading to serious problems—even death! Unpleasant symptoms include fever, stomach pain, feeling weak, weight loss, and even a belly that swells like a balloon. Leishmaniasis can cause weird wounds on the skin, too.

Dogs, our furry friends, can also be greatly affected by this sneaky parasite, which spreads more intensely in this species, causing a very serious illness. Dogs may begin to develop non-healing sores on their noses, ears, joints, and tails, along with scaly skin and hair loss. And that is not all! Dogs may have other signs such as lack of energy, loss of appetite, and rapid weight loss. While there are medications to treat leishmaniasis in dogs, some of them can have serious side effects. Vaccines are available for dogs, but unfortunately none are available for humans. There are several important ways to protect ourselves against leishmaniasis, however.

Global Changes are Affecting Sand Flies

Global changes are already affecting how leishmaniasis spreads, as these changes affect where sand flies live and how they behave. Changes to the physical environment play a big role in this story. Things that humans do, such as cutting down forests [3], can change where sand flies live, bringing them in closer contact with people and dogs. This makes it easier for them to bite humans and dogs and to transmit parasites more easily.

Changes in Earth’s climate can also make a difference (Figure 2) [4]. Warming temperatures make sand flies survive longer and cause them to have more offspring, increasing the number of sand flies in the environment. In the future, leishmaniasis will appear in places where it did not exist before. Warmer temperatures also increase the multiplication of parasites inside sand flies [5], so more Leishmania can enter the host at the time of the bite. If more parasites enter, the more serious the leishmaniasis will be.

There is also a very sad social aspect to leishmaniasis, since in a general sense it is strongly associated with poverty. Therefore, it can be considered a neglected disease. This happens because, in these areas of the world, the conditions are not so good—for example, people live in houses built with mud walls and earth floors, and keep domestic animals close to the main house, attracting sand flies and allowing them to breed and rest (Figure 3A) [6]. Furthermore, people in these communities often have difficulty accessing doctors, which delays the discovery of the disease and prevents them from receiving treatment early. This can make the disease more difficult to treat, and people become sicker. It is very important to ensure that everyone has access to the necessary healthcare—healthcare is a basic human right, and all humans should be treated fairly. This means that, beyond treating leishmaniasis, we should help communities that are in such difficult situations.

What Can We Do to Flip the Script?

How can we deal with the problems that sand flies cause? The search for new ways to reduce the impact of leishmaniasis needs to be based on sustainability. We must think about all the pieces of this huge puzzle. For example, we can no longer just focus on human health—we must also consider animals and the environment. Prioritizing prevention is essential to avoid the spread of sand flies and thus the spread of leishmaniasis. For preventive measures to be functional and long lasting, they must take into account the characteristics of each place. For example, dogs should be protected against sand flies with collars or pipettes containing insecticides. In this way, we not only protect our pets from being bitten by sand flies, but humans too.

If the entire community actively participates in control actions, people can learn together and feel like they have more control over the situation. Everyone can contribute with ideas and opinions, helping to find better solutions! Empowering communities to actively participate in disease-control efforts fosters collective responsibility and ensures the that disease-control programs work well and are successful now and in the future [7].

That is why projects like CLIMOS are so important. Picture this: for the first time ever, a bunch of researchers from across Europe, Türkiye, and Israel have come together to crack the code on how climate, environment, and social issues influence sand flies, and to try to predict where a lot of dangerous pathogens might spread (Figure 3B). CLIMOS is multidisciplinary, which means the project contains a cool mix of science, education, and health. CLIMOS uses both traditional and new methods to combat diseases. And they are not just leaving it to people who wear lab coats—they want everyone in this mission. Yes, you too! The main objective is to provide important tools to help create new policies, involving both scientists and the community, so that everyone can better protect themselves and their pets. These tools must be easy to understand and apply, no matter where people are, so that the project can work in diverse regions of the world. This will help us prevent leishmaniasis from spreading to places where it does not yet exist, so we can keep everyone safer and healthier. Are you ready to join this fight?

Glossary

Pathogen: ↑ A very small living thing, such as a virus, bacteria, or parasite, that can make a human or other living organism sick.

Parasite: ↑ An organism that lives in or on another organism to obtain food and survive.

Protozoa: ↑ Microscopic, single-celled creatures that can be free-living or parasitic. Some make people sick, like those causing malaria and leishmaniasis.

Host: ↑ The organism that harbors the parasite. The parasite lives inside or on the host, often causing harm.

Leishmaniasis: ↑ A disease caused by Leishmania parasites that affects humans and animals. It can cause different symptoms such as fever, sores on the skin or swelling of the belly.

Global Changes: ↑ Major transformations affecting the entire world, spanning environmental, social, economic, and political aspects, shaping how we live and interact globally.

Neglected Diseases: ↑ Diseases that mostly impact low-income regions (particularly tropical areas) where there are not enough resources for study, treatment, and control, leading to community problems and hindering economic growth.

Sustainability: ↑ Practices and strategies designed to meet present needs without harming future generations. Balances environmental and social aspects for long-term wellbeing.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

This study was co-funded by European Commission grant: 101057690 and UKRI grants: 10038150 and 10039289, and was cataloged by the CLIMOS Scientific Committee as CLIMOS number 014 (http://www.climos-project.eu). The contents of this publication are the sole responsibility of the authors and do not necessarily reflect the views of the European Commission, the Health and Digital Executive Agency, or UKRI. Neither the European Union nor granting authority nor UKRI can be held responsible. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. For the purposes of Open Access, the authors have applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission. The six Horizon Europe projects, BlueAdapt, CATALYSE, CLIMOS, HIGH Horizons, IDAlert, and TRIGGER, form the Climate Change and Health Cluster. The authors would also like to acknowledge Fundação para a Ciência e a Tecnologia for funding through contracts with GHTM (UID/Multi/04413/2020) and LA-REAL (LA/P/0117/2020).