Slutty Crocs

Chlamydia killing thousands of crocs
Anna Salleh
ABC Science Online

Monday, 18 September 2006

Chlamydia infects the back of the crocodiles' throats, causing an inflammation that blocks the airway (Image: Berrimah Veterinary Laboratories)
Chlamydia is suffocating thousands of young, farmed crocodiles in Australia's north, say experts.

Dr Ian Jerrett, senior veterinary pathologist at the Northern Territory government's Berrimah Veterinary Laboratories, says the disease is killing saltwater crocodiles (Crocodilus porosus).

"I think it's the first very serious disease of crocodiles that we've recognised since farming started," Jerrett says.

The disease affects young crocodiles, between three and five months old, causing an eye discharge and severe inflammation at the back of the throat that stops them from breathing.

"These crocodiles are dying from obstruction of the larynx," says Jerrett. "They can't breathe because of the amount of damage in the back of the throat."

The disease has been found so far on four of the five large crocodile farms in the Northern Territory, says Jerrett, with two farms seriously affected.

"One farm, over a period of two months, lost about 2000 of their young crocodiles, which was nearly the whole crop for that year," he says.

"And another farm lost over 1000 which was about 30% of their crop for the year."

At first a pox virus was suspected but virtually all the samples taken from the animals have since shown the culprit is chlamydia, unusual bacteria that need host cells to multiply.

The researchers will use DNA analysis to compare the strain to those that infect other animals such as wild birds. But they suspect it will be a strain specific to crocodiles.

The strain involved is related to the strains that infect columnar epithelial cells in the genitals and eyes of koalas and humans, says Jerrett.

But in crocodiles, columnal epithelial cells extend from the eye into the lining of the throat, which is why the chlamydia causes much more serious effects.

The bacteria, which are shed from the eyes, genitals and faeces of infected crocodiles, can be transmitted easily through the water in the ponds they are kept in, says Jerrett.

Origin unknown

Jerrett says further research is required to find out where the chlamydia came from.

He says the bacteria have probably existed at a low level for some time in the crocodile population, harboured in older crocodiles that can live with the bacteria their whole life.

The researchers believe an unusually cold dry season suppressed the immune system of the young crocodiles and made them susceptible to the bacteria.

So far the researchers have only detected chlamydia in a few older crocodiles, usually in those that have some other infection that has reduced their immunity.

If further testing reveals only a few of the older crocodiles are infected with chlamydia then Jerrett says the animals could be treated with antibiotics in their food.

But if the bacteria are widespread in the older animals then the disease could still spread despite antibiotics, which are not effective in treating 100% of animals.

In this case, the solution would be to quarantine the young crocodiles until they are old enough to withstand infection, says Jerrett.

The researchers have not yet sampled wild crocodiles, but Jerrett suspects the disease is more of a problem for farmed animals where large numbers are kept together in one place.

Apart from koalas and birds, chlamydia causes disease in animals like sheep and calves, and infects marsupials at a low level, says Jerrett.