Midges are tiny, two-winged flies that belong to several families, generally referring to any small, non-mosquito fly. The primary concern for disease transmission comes from biting midges, which are distinctly different from non-biting varieties that form large, harmless swarms. Biting midges act as vectors, acquiring pathogens from an infected host and transmitting them during a subsequent blood meal. The ability of these minute insects to spread viruses and parasites makes them a focus of public health and veterinary research worldwide.
Which Midges Pose a Threat
The most significant threat of disease transmission is posed by the genus Culicoides, which includes over 1,000 species commonly known as biting gnats, no-see-ums, or sand flies. These insects are small, measuring only 1 to 3 millimeters, and possess specialized mouthparts for cutting skin and drawing blood. Female Culicoides require a blood meal to produce viable eggs, driving their biting behavior on vertebrates, including humans and livestock.
These biting flies are found globally, from temperate zones to the tropics, and their life cycle is connected to damp environments. Culicoides lay their eggs in moist habitats, such as marshy ground, damp soil, or manure heaps, where standing water and high humidity create ideal conditions. Their peak activity often occurs during the twilight hours of dawn and dusk, though they can be active throughout the day in shaded areas.
Midge-Borne Diseases Affecting Humans
While biting midges cause intensely itchy bites and localized allergic reactions, their role in transmitting severe systemic diseases to humans is generally more geographically limited than that of mosquitoes. The Oropouche virus (OROV) is one of the most prominent pathogens transmitted to people by Culicoides. Oropouche fever is an acute febrile illness found predominantly in South America and the Caribbean, particularly around the Amazon Basin.
The primary vector for OROV is the biting midge species Culicoides paraensis. Symptoms typically begin with a sudden onset of high fever, severe headache, muscle and joint pain, chills, nausea, vomiting, and a rash. Most people recover within a few days to a month, though symptoms can sometimes return; in rare instances, OROV infection can lead to neurological complications like meningitis or encephalitis. The virus is maintained in a cycle involving midges and animal reservoirs, such as sloths, rodents, and birds, before being transmitted to humans. Recent outbreaks have shown the potential for the virus to spread beyond its traditional range, raising concerns about its emergence in new areas.
Midge-Borne Diseases Affecting Livestock
Biting midges represent a much greater threat to animal health and agricultural economies worldwide than they do to human health. Culicoides is responsible for transmitting numerous arboviruses to domestic and wild animals, acting as biological vectors for major diseases affecting ruminants and equids. One concerning midge-borne illness is Bluetongue Virus (BTV), a non-contagious disease primarily affecting sheep and cattle.
In sheep, BTV causes severe symptoms, including high fever, swelling of the face and tongue, excessive salivation, and internal hemorrhaging, resulting in mortality rates up to 30%. Although cattle infections are often asymptomatic, the virus can cause reproductive problems and congenital defects in calves. Another devastating disease is African Horse Sickness (AHS), which affects horses, mules, and donkeys.
AHS is caused by an Orbivirus transmitted by Culicoides midges, such as C. imicola. The disease requires the midge vector for transmission and has a very high mortality rate in horses, reaching up to 90% in the acute pulmonary form, characterized by high fever and severe respiratory distress. These livestock diseases pose immense challenges to animal husbandry, leading to trade restrictions and economic losses.
Protective Measures Against Midges
Effective protection against midges involves a combination of personal and environmental strategies designed to reduce exposure. Chemical repellents are recommended for exposed skin and clothing, with products containing active ingredients like DEET or Picaridin being the most effective. Oil of Lemon Eucalyptus is another active ingredient approved by the Environmental Protection Agency (EPA) that offers protection.
Physical barriers are also effective, as the small size of midges allows them to pass through standard window screens. Installing fine mesh screens on doors and windows prevents midges from entering structures, and wearing protective clothing minimizes exposed skin.
Modifying the environment around a property can reduce midge populations. Since Culicoides breed in damp conditions, eliminating potential egg-laying sites is crucial.
Environmental Modification
- Eliminate sources of standing water and ensure proper drainage of wet areas.
- Time outdoor activities to avoid peak midge activity around dawn and dusk.
- Place fans on patios or decks, as midges are weak fliers and cannot easily navigate strong air currents.