Researchers from Sydney’s Westmead Hospital and the University of Sydney confirm that fleas, although commonplace and regularly treated, are potentially more harmful than many people realise.  

There is nothing more common in a family home or a veterinary clinic than a pet with fleas. Persistent or reoccurring flea infestations on cats and dogs occur despite the variety of drugs and insecticides we treat them with, and a high level of owner compliance in Australia. Although they are considered animal pests, they are often overlooked in terms of their significance to human health in their competence as disease vectors and the impacts they make on our everyday lives. Studies have demonstrated that companion cats and dogs can be commonly infested with fleas carrying bacterial pathogens able to be transmitted to human owners. Research has made clear that there is much more to these irritating insects than meets the eye.

Fleas are wingless insects that have hematophagous adults, meaning they feed solely on the blood of their host. The immature flea stages, which includes tiny maggot-like larvae as well as pupae drop off the host into the environment such as carpet or soil until they emerge as adults. The most common flea encountered in Australia is the cat flea, Ctenocephalides felis felis. Despite their common name, these fleas are found on both cats and dogs. It is often assumed that if a dog has fleas, they must be dog fleas (Ctenocephalides canis). This is a common misconception. In fact, it appears as if the dog flea is something of a mythical creature in Australia. Despite historical records and anecdotal reports of dog flea infestations, there is no recent literature confirming their presence here.

Notwithstanding the economic impact of continual flea control treatments, the cat flea also carries zoonotic pathogens such as Bartonella and Rickettsia. Flea-borne disease may fly under the radar to some extent either because they are misdiagnosed as tick-borne illnesses or due to the presentation of generic fever and flu-like symptoms that rarely warrant further pathological investigation. Considering the highly ubiquitous nature of fleas in human environments, and the tendency of many species to be host generalists – particularly the cat flea – shouldn’t we be more concerned or at least more aware of the risk factors?

Given the impact these little parasites have on our lives, it is baffling how little we know about them. The genetic profile of the cat flea is highly understudied and yet within the genetic code lie hidden implications for the evolution of insecticide resistance, disease transmission and the passage of fleas across continents and the global sphere. A study on cat fleas collected from veterinary practices across five states of Australia showed that Australian fleas were 100% genetically identical at the mitochondrial DNA. This was a very unusual result as populations of other flea species are generally very diverse. The result was comforting news at the time for the regulation of veterinary pharmaceuticals, as the efficacy of flea control products were able to be compared against flea populations across the entire country. In 2014 we performed a second study revealing an additional Australian genotype geographically restricted to tropical northern Queensland. Despite this, it appears that institutional and commercial flea colonies in Australia and internationally may be working solely with the first common cat flea genotype.

If fleas from Australia are genetically similar, what about elsewhere? When fleas from Australia were compared to those collected from Thailand, Fiji and Seychelles, the results showed that from a global perspective, cat fleas are genetically diverse. Similarly, central European fleas from the Czech Republic and Romania show similar high genetic diversity, despite the presence of the common genotype as well (unpublished data). This may indicate that the common genotype is globally ubiquitous but possibly not dominant elsewhere.

A change in the genetic makeup of Australia’s flea population has implications for the control of fleas and the pathogens they carry and transmit to animals and humans. It is hoped that my research will yield a greater understanding of the cat flea genetic puzzle both locally and overseas and consequently contribute to the effective control of these tenacious blood- sucking creatures and the diseases they carry.

An understanding of the relationships between fleas, pathogens, companion animals and wildlife is critical for the development of surveillance systems to prevent flea-borne disease outbreaks, as well as effective flea control strategies. Future studies are also underway to determine the role fleas play in public health risk in Australia. The development of rapid diagnostic tests for flea-borne pathogens will allow investigations into the role the cat flea may play as a vector of zoonotic pathogens in family homes.

More information on fleas.

Andrea L. Lawrence1,2, Cameron Webb1,3, and Jan Šlapeta2

1 Marie Bashir Institute of Infectious Diseases and Microbiology, University of Sydney
2 Faculty of Veterinary Science, University of Sydney
3 Medical Entomology, Pathology West – ICPMR Westmead Hospital

Andrea Lawrence is a PhD student at the University of Sydney studying the common cat flea (Ctenocephalides felis) and related species. She collects samples from all over the world in her attempt to understand the variations in the global cat flea population and how those differences may affect their ability to carry and transmit disease to humans. Andrea can be contacted at [email protected]

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