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BED BUGS AS VECTORS OF DISEASE?

A guest article courtesy of Frances McKim from Pest magazine in the UK takes a look at a recently published bed bug study.  

A press release issued in November 2014 to coincide with the publication of a scientific paper in American Journal of Tropical Medicine and Hygiene has caused more than a few ripples in the scientific community.

A new study from Penn Medicine researchers in the Center for Clinical Epidemiology and Biostatistics demonstrated that bed bugs, like the triatomines (‘kissing bugs’), can transmit Trypanosoma cruzi, the parasite that causes Chagas disease, one of the most prevalent and deadly diseases in the Americas.

The role of the bloodsucking triatomine bugs as vectors of Chagas disease – which affects six to eight million worldwide, mostly in Latin America, and kills about 50,000 a year – has long been recognised. The insects infect people not through their bite but faeces, which they deposit on their sleeping host, often around the face, after feeding.

Bed bugs, on the other hand, are usually considered disease-free nuisances whose victims are left with only itchy welts from bites and sleepless nights.

In this study published online, senior author Dr Michael Z Levy, assistant professor in the Department of Biostatistics and Epidemiology at the University of Pennsylvania’s Perelman School of Medicine, and researchers at the Universidad Peruana Cayetano Heredia in Peru conducted a series of laboratory experiments that demonstrated bi-directional transmission of T. Cruzi between mice and bed bugs.

The significance of this study is that, to date, there has only been debate, rather than hard evidence, as to whether bed bugs transmitted any disease. As a result, bed bugs have always been classified as simply a nuisance pest so failing to attract the level of public health concern, and associated funding, as other pests that do transmit disease, such as the malaria mosquito, have done.

So what does this mean? Two bed bug experts were asked for their reaction to this published research.

First, Clive Boase from the Pest Management Consultancy, UK said: “This is an interesting study, and contributes to a thread of research on bed bugs and human trypanosomiasis (Chagas disease), that stretches back decades. In South America, human trypanosomiasis is a potentially fatal disease that is transmitted between people largely by blood-feeding reduviid bugs that live in cracks and crevices in rural dwellings. Since 1991, there has been an international program across South America to eradicate the bug, using indoor treatments with residual insecticides. This has been successful in many areas, and the incidence of the disease has fallen dramatically.

“The suggestion arising from this latest study is that even if the reduviid bugs are eradicated, then bed bugs could become a new vector of this disease, and reverse all the progress made in the last quarter century.

However, despite the long co-existence across South America of people, bed bugs and the Chagas disease pathogens, there is no indication that bed bugs are actually transmitting it to people. Nonetheless, those responsible for managing the Chagas eradication work in South America should be looking out for cases of local transmission of Chagas in areas where the reduviid bugs have been eradicated.

“Of course human trypanosomiasis does not occur naturally in the UK, but interestingly, there is a species of trypanosome that does occur naturally in the UK, in bats, and it is transmitted between bats by, yes, you guessed it, the bat bug Cimex pipistrelli!” concluded Mr Boase.

From Australia, Stephen Doggett from the Department of Medical Entomology at Westmead Hospital, New South Wales commented: “To be honest, the result is not all that surprising. Trypanosomes were always going to be the best candidate of all pathogens for the transmission by bed bugs. However, the fact is just because a laboratory experiment demonstrates that an insect is a good vector in the lab, it does not necessarily mean that this is the case in the field. Such information must be backed up by epidemiological evidence, and this does not presently exist.

“There still is not one piece of evidence that bed bugs have ever transmitted any pathogen to any human, and that the risk of them doing so is extremely small if not negligible. Just because we have bed bugs in more economically advantaged nations, does not mean that we will see the establishment of Chagas disease; our good health infrastructures will ensure this will not happen.

“Thus I suspect that this paper will make a lot of noise as many scientists want evidence that bed bugs transmit disease causing pathogens, simply to improve their chances of gaining research funding. Thus we need to take this paper in the context of what it is, no big surprise and really of very little scientific consequence, as there is no risk to those bitten in non-endemic areas for the disease.”

Frances McKim, Editor, Pest Magazine