Finally, after hinting at it in several exotic threads, someone asks me the correct question (I would have hoped someone would have gone and researched it themselves as I've hinted at where to look too).
Here are the diseases/parasites/microroganisms carried by snakes (not worrying about lizards) that are not presently found in Australia:
Leptospira spp.
Alphavirus (Eastern equine encephalomyelitis virus (EEEV), Western EEV, Venezuelan EEV)
Japanese encephalitis virus
Mycoplasma spp.
Adenoviridae (Snake adenovirus)
Gammaretrovirus (Viper retrovirus - formerly reptilian type C oncovirus)
Herpesviridae (Boid herpesvirus I, Elapid herpesvirus I)
Iridovirus (Snake erythrocytic virus)
Ophidian paramyxovirus (Fer de lance virus)
Ranavirus (Wamena virus)
Reoviridae (Python orthoreovirus, Rattlesnake orthoreovirus)
Retroviridae (Inclusion Body Disease of Boids)
Amplicaecum spp.
Camallanides spp.
Camallanus spp. from snakes
Dracunculus spp.
Eustrongylides spp.
Gnathostoma spp.
Hexametra spp.
Kalicephalus spp.
Macdonaldius spp.
Meteterakis spp.
Ophidascaris spp.
Paracapillaria spp.
Physalopterinae (Abbreviata spp., Physaloptera spp., Skrjabinoptera colubri)
Rhabdias spp.
Strongyloides spp.
Terranova caballeroi
Travassosascaris araujoi
Bothridium spp.
Crepidobothrium spp.
Mesocestoides spp.
Oochoristica spp.
Spirometra spp.
Encyclometra spp.
Neodiplostomum major, N. spathoides, N. [Fibricola] seoulense
Ochetosoma spp.
Pneumatophilus spp.
Pulmovermis cyanovitellosus
Styphlodora spp.
Xenopharynx spp.
Centrorhynchus spp.
Sphaerechinorhynchus spp.
Porocephalidae (Armillifer spp., Kiricephalus spp., Porocephalus spp.)
Amblyomma spp.
Aponomma spp.
Ixodes ricinus
Ornithodoros spp.
Caryospora spp.
Eimeria spp.
Isospora spp.
Sarcocystis spp.
Tyzzeria boae
This list was compiled 4 years ago, since then three or four of the above organisms have been identified in captive collections, none have been found in wild snakes - yet.
Hix