Trials of a new vaccine for a virus affecting farmed crocodiles are aiming to open the door to the development of human vaccines for dengue and zika.
Kunjin virus is transmitted by mosquitoes and causes lesions in the valuable skins of infected crocodiles.
However, the technology used to create the vaccine is more than skin deep, offering broad applications for a spectrum of mosquito-borne pathogens including those affecting humans.
The reptilian infections were discovered only 12 months ago.
University of Queensland professor Roy Hall said scientists are still learning about how the transmissions occur and why they create skin sores.
“Probably the mosquitoes bite through soft areas of the body, particularly around the eyes of the crocodile. That’s from some observations that people have had on the crocodile farms,” he said.
“Because the skins of crocs are very important for developing these high-end fashion leather accessories, even small lesions can destroy the quality of the skin.
“Exactly why the lesions occur in certain places we don’t know.”
The scientific team has applied to the Office of the Gene Technology Regulator to conduct field trials on crocodile farms, initially in the Northern Territory and potentially in far north Queensland.
Vaccine combines viruses
Professor Hall said the kunjin vaccine is a hybrid of mosquito-borne viruses.
“We discovered these really interesting flaviviruses that were carried by mosquitoes in northern Australia that are very distantly related to kunjin and dengue and so forth, but the interesting thing is they don’t infect man or animals so they’re really useful as a base for a vaccine because they’re quite safe,” he said.
“We’ve added a couple of proteins from the kunjin virus that make up the shell of the virus particle and these are the components that the body sees when we develop immunity to infection.
Preliminary studies on mice in the laboratory have shown the vaccine provides good protection after two doses, but the scientists have not yet received approval for trials on larger animals.
“On a farm that has tens of thousands of animals we’ll be only using about 70 juvenile crocodiles per group,” Professor Hall said.
“That’s to optimise the dose, the route of inoculation, so we can maximise the effect of the vaccine to get the best protection possible.”
He said because the virus cannot replicate in vertebrate cells there is a very low risk of the genetic material spreading.
“Once we inoculate the crocodiles the immune system of the crocodile rapidly clears the virus from the body,” Professor Hall said.
“So within a matter of hours the virus is gone, and because it can’t replicate it can’t be transmitted and spread to other animals. That’s what makes it very safe.”
The five-year trial will provide scientists with a large animal model to test the technology, with a view to developing vaccines for other large animals, including humans.
“So potentially it has a market in other species, particularly man.”
Skin trade spurs research
The scientists researching the condition have developed the vaccine through a $4.8 million crocodile disease control project led by Northern Territory crocodile farming business Porosus Pty Ltd.
The Federal Government has contributed $1.15 million in funding through the CRC for Developing Northern Australia.
Porosus owner Mick Burns said the project is aimed at enabling Australian crocodile producers to become more globally competitive.
“The international market is currently in a state of oversupply so it’s pushing everyone to produce the best of skin that they can and Australia is probably one of the countries that’s leading the world with smart farming.”
“It’s a real win-win if we get the results that we’re hoping for.”
Crocs act as guinea pigs
The National Health and Medical Research Council has granted funding for Professor Hall to use the so-called safe flaviviruses to develop hybrid vaccines to protect humans against mosquito-borne infections.
“The potential of this is now being recognised,” he said.
However, Professor Hall said it takes a lot longer for human vaccines to receive approval, so clinical trials are still several years away.
“We have to complete all our small animal studies in the laboratory for all these different vaccines and once we’ve confirmed how efficient and safe they are, then we can move forward into clinical trials,” he said.