Putting the bite on midges in the US: Feeding habits put under scrutiny

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Culicoides biting midges are present across most of the globe, playing key roles in the transmission of several important diseases that can affect horses and livestock.

Among the most damaging Culicoides-borne pathogens are those that cause African horse sickness, bluetongue, epizootic hemorrhagic disease, vesicular stomatitis, and Schmallenberg, the livestock disease first reported in 2011.

Each of these viruses also causes outbreaks in wildlife and livestock globally that have been linked to severe economic losses and disease-related trade restrictions.

Researchers in the United States set out to identify the diversity of vertebrate hosts that Culicoides feed upon, saying it was a way to increase knowledge about the evolution and ecology of Culicoides species and the pathogens they transmit.

Matthew Hopken, Bonnie Ryan, Kathryn Huyvaert and Antoinette Piaggio used molecular-based testing to identify the Culicoides species and their blood meals.

A total of 366 blood-engorged specimens from three states, New York, South Carolina, and California, were gathered between 2011 and 2014, with the researchers ultimately able to identify the sources of the blood meals from 199 of them.

They detected DNA from 12 host species across seven different Culicoides species, details of which are given in the table below. The hosts included both mammals and birds. Black-tailed deer were the most common meal identified, numbering 74, followed by cattle (34), sheep (24) and horses (22).

A breakdown of the blood meals eaten by 199 Culicoides biting midges. Tavle: Hopken et al, Parasites & Vectors
A breakdown of the blood meals eaten by 199 Culicoides biting midges. Tavle: Hopken et al, Parasites & Vectors

“We documented new host records for some of the Culicoides species collected,” they reported in the journal Parasites & Vectors.

Most of the mammalian hosts were large ungulates but they also detected a lagomorph [a jackrabbit] and a carnivore [dogs].

Bird species that were detected included a house finch and emus, the latter providing evidence that Culicoides variipennis species do not feed only on mammals.

“The main finding from this study was that North American Culicoides host choice was broader than previously understood,” Hopken and his colleagues wrote.

“We identified a diversity of known hosts, including some that are highly susceptible to infection with bluetongue virus and and epizootic hemorrhagic disease virus, and expanded the catalog of hosts through detection of previously undocumented vertebrate host species.”

The results, they said, show that Culicoides will feed on multiple classes of vertebrates and may be more opportunistic in regards to host choice than previously thought.

“This knowledge can help with identification of susceptible host species, pathogen reservoirs, and new vector species which, in turn, will improve disease outbreak risk assessments.”

They said vector-borne pathogens were significant threats to the health and welfare of both humans and animals worldwide.

“More investigations into the ecology of all Culicoides species, not just the currently known vectors, will lead to better predictions of disease outbreaks and their attendant negative impacts on animal and human populations.

“In the face of climate change, the distributions of vector species and pathogens are expected to change.”

The potential existed for Culicoides-borne pathogens restricted to warmer parts of the world to move north or south, leading to devastating outbreaks.

“With the continuous threat of the introduction of foreign pathogens, we must build a solid foundation of knowledge regarding Culicoides host choice so that we can develop better models to predict transmission and to develop methods to study and manage Culicoides and the pathogens they transmit.”

They said their dataset was the most comprehensive blood meal analysis for North American Culicoides to date.

Picky eaters are rare: DNA-based blood meal analysis of Culicoides (Diptera: Ceratopogonidae) species from the United States
Matthew W. Hopken, Bonnie M. Ryan, Kathryn P. Huyvaert and Antoinette J. Piaggio.
Parasites & Vectors 2017 10:169
DOI: 10.1186/s13071-017-2099-3

The study, published under a Creative Commons License, can be read here

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