A rare infectious disease thought to be non-existent in the southern hemisphere has been discovered in Australia by researchers from the University of Sydney.
Tularemia is a highly infectious and potentially deadly disease caused by the bacterium Francisella tularensis that affects humans and animals. It has been endemic to North America and Eurasia for centuries but was thought to be non-existent in the southern hemisphere.
However, researchers have found the disease to exist in wild ringtail possum populations in Sydney as part of an investigation of unexplained animal die offs in collaboration with the Australian Registry of Wildlife Health at Taronga Conservation Society Australia, and also following two human cases of tularemia in Tasmania in 2011. This discovery was enabled by the innovative application of new genomic techniques and bioinformatics methods established by the University of Sydney researchers.
Co-author of the report published in Emerging Infectious Diseases, Dr John-Sebastian Eden from the Faculty of Science says the disease can be deadly if left untreated.
“Tularemia is an infectious disease that needs to be treated. If an infected person doesn’t seek treatment then the disease could become deadly. With that being said, appropriate antibiotics can target the disease effectively so it’s important we identify any cases.”
“The main concern is that the disease is particularly potent when inhaled; it settles in the lungs which makes treatment more difficult,” he says.
Associate Professor Vitali Sintchenko from Sydney Medical School says there are three ways the infection can develop and each may lead to different clinical symptoms.
“The development of Tularemia can take several forms. For example, the ulceroglandular form can occur from a bite by an infected animal or tick and the bite site will become painful followed by the nearby lymph nodes becoming inflamed and enlarged in size.
“Another form is oropharyngeal which can develop after drinking contaminated water. This form is characterised by abdominal pain, vomiting and inflammation of the throat. The third form is pneumonic, which develops after inhalation of aerosols infected with Francisella tularensis and it can lead to severe pneumonia. In many cases up to a third of patients with severe disease may die if this uncommon infection is not recognized and treated,” he says.
Associate Professor Sintchenko adds that there is no risk of the infection being transferred from a person with the disease to other humans, and the appropriate antibiotics, prescribed once the diagnosis is confirmed by accredited laboratory tests, reduce the duration of symptoms and risks of complications.
“Infection in humans is the end stage for the pathogen. The disease is transferred from infected animals to humans by direct exposure or through vectors, i.e. tick bites,” he says.
Typically the disease is carried by a wide range of animal hosts but has been most prevalent in wildlife such as rabbits and rodents. In Australia the disease has been found to be carried by ringtail possums and transmitted to humans by bites or scratches.
“The cases we have seen have all been related to ringtail possums. However, in countries such as the US where the disease is endemic it’s also carried by mosquitoes and ticks. The majority of reported cases in the States is from people who have been infected due to a tick bite,” says Dr Eden.
Tularemia is mainly contracted through direct exposure to infected animals during hunting as well as through biting insects such as ticks and mosquitoes while waterborne and environmental sources have also been reported.
Dr Eden says that a commonsense approach to animals and animal bites will often be enough to prevent or treat the infection.
“If you do get bitten or scratched and the site of this bite is painful and infected go to your doctor immediately. A simple course of antibiotics should prevent a Tularemia infection setting in. Possums are nocturnal so if you see one that’s active in the day then there is a good chance it may be sick.
“My advice would be to stay away from any animal that appears to be sick or injured as their general response will be to attempt to bite or scratch, and call an animal services body such as Animal Health Australia to handle it. If you must handle wildlife, wear gloves and make sure the animal is well restrained.”
“This research also indicates that clinicians should be aware of Tularemia and for the disease to be considered when treating systemic infections following insect and animal bites.”
(Source: The University of Sydney, Emerging Infectious Diseases)