Biting midges: the smallest blood feeding dipteran, neglected but important14/10/2017
Carlos Brisola Marcondes
Full professor at the Department of Microbiology, Immunology and Parasi-tology (MIP) at the Biological Sciences Center (CCB) at the Federal Univer-sity of Santa Catarina (UFSC)
A recent report of infection cases by the Oropouche virus in Salvador and nearby cities has drawed attention towards the small biting midges. The study of these dipteran flies, the smallest blood feeding insects, has been neglected, for their size (1-2 mm), and sometimes even 4 mm and for apparently being simply annoying.
In fact, they are annoying, especially when striking in large groups, inclusive dropping real estate and local prices due to the allergenicity of its saliva. Tourism can be strongly affected, since the ones tolerance is much smaller when in vacation than when living or working somewhere. Besides discomfort caused on humans, they can cause a dermatitis (sweet itch) in equines. As an Australian expert once said: One biting midge is an entomology wonder, a thousand are hell.
They have also been held responsible for transmitting at least 50 arboviruses. The Bluetongue and Schmallenberg viruses have been reported in several ruminants. The first takes place in several continents with various serotypes, being reported in almost all South American countries; it causes major damage to sheep livestock and is poorly studied in Brazil. The second has been broadly reported in Europe, and causes large damages to cattle. Europeans are very concerned with the African Horse Sickness, also caused by viruses transmitted by biting midges, causing great prejudices when infecting horses, especially if sports related animals; outbreaks have killed over 70 thousand horses (40% of the livestock) in Cape (South Africa) and 300 thousand from Cyprus to Afghanistan. Several other viruses (orthobunyavirus, orbivirus and rhabdovirus) strike livestock in Japan. Considering the importance of livestock industry in Brazil, it is necessary, to give these arboviruses special attention.
Humans have been affected by the Oropouche virus, causing dengue-like symptoms, sometimes resulting in epidemics striking great part of the populations, as happened in Serra Pelada. Before apparently restricted to the Amazon region and countries in the far north of South America, it has currently been reported in other areas. Even not causing (yet) any deaths, it can inflict great suffering and temporary inabilities.
Mansonelliasis is usually related to biting midges, a neglected disease of broad distribution in the Americas and in Africa. It not only causes problems per se, but also triggers complications for diagnostic and treatment of other filariasis.
There are indications of biting midges role transmitting several Leishmania from the enrietti group, especially in Australia. These barely known trypanosomatidae take place in Africa (Ghana), and cause visceral and cutaneous leishmaniasis in Southeast Asia, Australia – infecting kangaroos and in Brazil, with L. enrietti and L. forattini, apparently restricted to rodents. In Australian studies, none of the 1,818 examined Sergentomyia sandflies returned positive results, but even apparently infecting forms (similar to metacyclic promastigotes) were found in biting midges; all there is left to find is experimental transmission by these insects. Besides this, even not being possible to incriminate them for transmitting L. braziliensis and L. amazonensis, they were found with DNA from these protozoa in Maranhão State.
Biting midges have a varied biology, and its immature forms are found in several environments, including rotting fruits, still water in different types of soil, bamboo internodes, water with manure, etc. Adults can fly hundreds of meters and be transported for great distances by the wind, and bite more frequently at dusk, but some species will attack any time of the day. Despite associating biting midges to mangrove vegetation, there are species whose larvae develop in rotting vegetables (cocoa and banana trees); some places with banana plantations in Santa Catarina (Corupá) have an irritating amount of biting midges. In Salvador, a study from 1964 already described skin problems caused by biting midges in the city, with large predominance of Culicoides paraensis, involved in transmitting Oroupouche viruses in Pará and other areas.
Control is very difficult, especially with little knowledge of the fauna and biology. Installing screens in houses and barns in inefficient, since they must be so small that ventilation would be compromised; even when they are impregnated with insecticide they are not able to totally stop these small insects from going through, which is mandatory if the intention is to avoid arboviral diseases. Insecticides are little efficient, whether applied in facilities of on animals, and repellents have many limitations, especially for horses. Insecticide spray costs are too high for frequent use.
For its small size, it is necessary to dissect them for identification, and for not having (so far) indications of major medical or veterinary importance, its study is not popular and funding is directed to other dipteran, as mosquitos and sandflies.
The biting midges fauna in Brazil, includes nearly 500 described species, needs the dedication of a much greater amount of researchers, currently a few dozens, surely underfunded. It is a very important group, and we cannot wait until more serious problems with arboviruses arise to develop staff and researches. We do not train firefighters after the fire begins, but before.…