Mysterious new disease posing 'emergent global threat for humans' is carried by mosquitoes

Rickettsia felis previously thought to only be transmitted by fleas and ticks

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Scientists have discovered yet another reason to despise mosquitoes, after it emerged that the insects are potential carriers of a mysterious and “poorly understood” new disease.

First described by experts in 1990 and identified in 2008 as an “emergent global threat for humans”, very little research has been done into the dangers posed by the bacteria Rickettsia felis.

It causes symptoms similar to many bacterial infections, and recent research found it was often found in cases where doctors registered an illness as “fever of unknown origin”.

This was particularly the case in malaria-endemic areas – and sure enough, a study in which mosquitoes were fed on Rickettsia felis-infected mice found that the insects were able to transmit the disease.

Also known as cat-flea typhus, the disease made headlines in Australia in 2009 when the mysterious case of an infected nine-year-old girl sparked what was described as “a lengthy investigation similar to those featured in the hit TV series House”.

Philippe Parola, one of the new study’s co-authors, told that so little is known about infections of Rickettsia felis in part because it can only be identified by a laboratory diagnosis.

The symptoms of the disease are ill-defined and easily confused with other diseases, he said – meaning the disease is almost certainly under-diagnosed in humans.

Even when it was thought that Rickettsia felis was only transmitted by fleas and ticks, the disease was considered by the Centres for Disease Control and Prevention as “representing a high potential risk for public health”.

Speaking about Rickettsia felis in 2010, the CDC’s Dr Chris Paddock said: “What’s interesting about this particular Rickettsial disease is that it’s been described on nearly every continent around the world, except for Antarctica.

“There have been no known deaths attributable to Rickettsia felis infection. Nonetheless, because it’s so broadly distributed, we think that it’s probably a very important Rickettsial disease.”

The new research by Professor Parola et al appeared in this week's Proceedings of the National Academy of Sciences.