Tick genome

International genome and proteome databases now hold massive data sets on scores of life forms, from bacteria to mice and humans, but there is no tick genome, even though ticks are serious parasites of humans and livestock.

In the US, ticks transmit the rickettsial infections Lyme disease and Rocky Mountain spotted fever, and babesiosis in cattle. There is some evidence that I. holocyclus is the vector for a native rickettsia that causes a Lyme-like disorder in some people and pets.

Padula says the lack of a tick genome database or proteome library makes it very difficult to identify tick proteins and establish their function - Purdue University in the US has recently begun a tick genome project, but it will be some time before the database is sufficiently annotated to be useful to immunologists.

So the UTS team is doing de novo peptide sequencing of tick proteins and enzymes, trying to determine their function by matching them up in databases for other arthropods.

In addition to salivary enzymes, they are looking for other soluble proteins that may mute the host's defensive responses.

By running sequential extractions, they are extracting proteins that vary from soluble to hydrophobic. The former are likely to include allergens, while the latter may include membrane-bound proteins from tick cells.

In the 1980s, CSIRO immunologists attempted to develop a vaccine against gut antigens from cattle tick, Boophilus microplus, that would destroy the lining of the tick's gut, causing it to starve and drop off the animal.

If the UTS centre succeeds in isolating candidate tick antigens, they will probably be handed over to vaccine developers to work with. Padula is using the tick as a model for developing novel proteomics techniques that can be applied to a variety of "orphan species" for which no genome or proteome data are available - and may not be available for decades, if ever.

"The tick is an interesting organism. It forces you to think about developing interesting new ways to purify and identify proteins," he says.

The centre is running projects on a number of other economically important parasites, including the pathogenic yeast, Cryptococcus neoformans, which can cause cryptococcosis - a chronic infection in immunosuppressed individuals, with symptoms including inflammation of the heart and brain.

The centre is also comparing protein-expression profiles for normal and bleached coral polyps.

Padula's PhD is currently funded at the discretion of the centre, and he fears the project may be wound up without delivering enough candidate antigens to interest a commercial developer, when he completes his research early next year.

"A tick vaccine would save an enormous number of pets and livestock," he says. "Veterinarians are certainly interested - they're always asking me when a tick vaccine will become available."