A University of Sydney researcher has discovered a new species of fungus, named Aspergillus felis that causes life-threatening infections in humans, cats and dogs and is frequently resistant to available treatment.
The fungus is not only resistant to some of the very powerful anti-fungal drugs used for treating these infections in people, but has also very likely been under diagnosed due to the fact that it looks very similar to another fungus called Aspergillus fumigatus.
"Two people with known immunodeficiencies are known to have died from infection with Aspergillus felis," says Dr Vanessa Barrs, Associate Professor and researcher from the University’s Faculty of Veterinary Science. "Both cats and people are infected with the fungus from the environment. Cats don't pass the fungus on to humans or vice versa; infection occurs when the spores are breathed in."
What Is Asperigillosis?
Aspergillosis is the name given to infections caused by Aspergillus fungi, which live in the soil and their spores are disseminated in air currents. Humans generally inhale several hundred spores each day, but they are efficiently eliminated by a healthy immune system.
"The likelihood that infection will occur after inhalation of spores largely depends on host factors such as immunosuppression," says Associate Professor Barrs. "As the number of immunosuppressed patients worldwide rises, invasive aspergillosis has emerged as a major problem. Those at greatest risk include people with blood cancer (eg leukaemia), organ transplant recipients, individuals receiving high-doses of immunosuppressive drugs and people with white blood cell deficiencies or dysfunction."
Although there are more than 400 species of Aspergillus, fewer than 40 have been documented to cause disease in humans or animals, and some of these have been reported only once. Aspergillus fumigatus accounts for most human cases of aspergillosis.
A/Professor Barrs discovered the fungus when she first spotted an unusual fungal infection in three cats she was seeing at the University’s cat treatment centre in 2006. The cats presented with a tumour-like growth in one of their eye-sockets that had spread there from the nasal cavity.
"The fungal spores are inhaled in air and in susceptible cats they establish a life-threatening infection, called sino-orbital aspergillosis, that is very difficult to treat," she says.
After six years of investigation, including working with some of the world’s leading fungal experts at the CBS-KNAW Fungal Biodiversity Centre in The Netherlands, A/Professor Barrs was finally able to confirm this as a completely new species which can cause dangerous disease in humans and cats by infecting their respiratory tract.
"Similar to the closely-related fungus Aspergillus fumigatus, this new species of fungus can also reproduce asexually and sexually," says A/Professor Barrs, whose findings have been published in PLoS One, a peer-reviewed Journal from the Public Library of Science.
The Fungus Affects Healthy Cats
The new species is Aspergillus felis and since its first sighting more than 20 sick domestic cats from around Australia and one cat from the United Kingdom have been diagnosed as having been infected by the fungus. In the two humans identified as being infected by the fungus, it attacked an already highly compromised immune system but, by contrast, it appears to infect otherwise healthy cats, explains A/Professor Barrs.
Although the disease is not passed between humans and cats, its study in cats will not only help their treatment but also provide a good model for the study of the disease in people.
"There is only a 15 percent survival rate of cats with the disease and it has so far proved fatal in humans. To date only one case has been identified in a dog," she says. “We are right at the start of recognising the diseases caused by this fungus in animals and humans. The number of cases may be increasing in frequency or it may just be we are getting better at recognising them."
Fungi like Aspergillus felis can be easily misidentified as the closely related fungus Aspergillus fumigatus, which is a well-studied cause of disease in humans. However, A. felis is intrinsically more resistant to antifungal drugs than A. fumigatus and this has important implications for therapy and prognosis, she explains.
The next step for A/Professor Barrs and her team is studying fungi in culture collections throughout Australia to determine the prevalence of A. felis infections in people with previously diagnosed aspergillosis.
Topic: Owning a Pet, Cats, Dogs