When we talk about disease-transmitting insects, the first thing that comes to mind are mosquitoes such as Aedes aegypti, which is mainly responsible for spreading dengue, chikungunya, Zika, and yellow fever. However, other tiny insects can also be disease vectors and often go unnoticed. These include Culicoides, a genus of small flying insects that can transmit viruses dangerous to humans. In particular, Culicoides paraensis is primarily responsible for the transmission of Oropouche virus in the Region of the Americas.
What are Culicoides or midges?
Culicoides is a genus of very small insects that are only 1–5 millimeters in size, making them difficult to identify. They are popularly known as “biting midges”, “no-see-ums”, "jejenes", "mosquitos polvorilla" or "chaquistes", in different parts of the Region. In Brazil, they are known as "maruim", "mosquitinho-do-mangue". Though tiny, they are hematophagous insects, meaning that they feed on blood, and some species can transmit diseases to humans and animals.
Culicoides paraensis and Oropouche virus
One of the species most relevant to public health is Culicoides paraensis, the main vector of Oropouche virus in the Americas, which causes Oropouche virus disease (OROV), characterized as a febrile infection that produces: headache, muscle pain, and general malaise, symptoms similar to those of dengue fever. Though not usually fatal, Oropouche fever can affect many people in epidemic outbreaks, especially in tropical regions.
Since late 2023, OROV outbreaks have been reported in several countries in South America and the Caribbean, including areas with no previous history of the disease.
There is no specific treatment or vaccine for OROV. Management of the disease includes rest, hydration, and use of medications to control fever and pain, as well as monitoring for possible complications.
Ecology and life cycle of biting midges
Biting midges have a four-stage life cycle: egg, larva, pupa, and adult. Larvae usually develop in moist places such as muddy soil, decaying leaves, or stagnant water. This is a key point because in rural and suburban tropical areas such sites are extensive and abundant, making it difficult to identify areas where they can reproduce and to take measures to control them.
Adult midges are mainly active in the late afternoon, but they can also be active at night. They are attracted to carbon dioxide exhaled by humans and to body heat, leading them to bite humans and other animals in order to feed on their blood. Both males and females feed on plant nectar, but only females need blood for their eggs to develop.
What do they feed on and what is their role in the ecosystem?
Culicoides do not only bite humans; they also feed on the blood of mammals, birds, amphibians, and reptiles. This makes them important disease vectors, as they can transmit viruses between different species.
However, despite their bad reputation, midges serve important ecological functions. They are a food source for bats, frogs, fish, and other predatory insects. In addition, by feeding on flower nectar, they help pollinate some plants.
Differences between Culicoides and Aedes mosquitoes
Although midges and mosquitoes such as Aedes aegypti can both transmit diseases, they have several key differences:
Size: Midges are smaller than mosquitoes and are hard to identify.
Bite: A midge’s bite is usually more painful than a mosquito’s and can cause allergic reactions in some people.
When they are active: While Aedes aegypti mosquitoes bite mainly during the day, Culicoides midges are most active in the late afternoon. However, they may also bite at other times, depending on the availability of their food source.
Reproduction sites: Mosquitoes such as Aedes aegypti generally lay their eggs in clean, standing water, while Culicoides biting midges prefer moist soil and decaying organic matter.
How to prevent contact with biting midges
To reduce the risk of bites and prevent diseases such as Oropouche fever, the following measures can be taken:
Wear clothing that covers most of the body: Sleeved shirts and long pants help protect the skin.
Apply repellent: Repellents recommended by health authorities can help keep midges away. Always check the manufacturer's instructions and recommendations before applying a repellant.
Install mosquito nets: Due to their small size, midges can get through conventional nets, so it is advisable to use fine-mesh netting.
Avoid high-presence areas: If possible, avoid areas with standing water or dense vegetation at dusk and at nightfall.
How to prevent the proliferation of midges
To reduce the number of biting midges in the environment, measures can be taken to eliminate their breeding sites:
Drain puddles and pools, and remove standing water from gardens and patios.
Keep areas surrounding the home clean, removing decaying leaves and accumulated organic matter.
Improve drainage in wet areas to prevent mud and moisture from accumulating.
Though midges are very small, they can present a public health problem, especially where OROV is circulating. To key to preventing their proliferation and avoiding bites is to know their behavior and where they reproduce. This will help reduce the risk of contagion and protect health. Being informed is the best tool to prevent diseases!
PAHO/WHO, in collaboration with the countries of the Americas, implements various strategies to strengthen technical capacities for the prevention, control, and elimination of vector-borne diseases. These include the development of evidence-based guidelines and technical documents, training of professionals in entomological surveillance and vector control, and promotion of innovative interventions. In addition, cooperation between countries is promoted through workshops, technical meetings, expert networks, and the strengthening of outbreak monitoring and response systems. PAHO/WHO also supports the implementation of national integrated vector management plans, promoting the rational use of insecticides and sustainable strategies to reduce the burden of vector-borne diseases.
