Infection with Xenohaliotis californiensis

Signs of disease

Important: animals with disease may show one or more of the signs below, but disease may still be present in the absence of any signs.

Disease signs at the farm level

• reduced feeding
• inability to adhere to substrate

Clinical signs of disease in an infected animal

• atrophy of the foot muscle
• wasting of body mass
• diminished reproductive output
• high predation

Gross signs of disease in an infected animal

• atrophy of tubules
• an increase in connective tissue
• inflammation and metaplasia of the digestive gland

Disease agent

Withering syndrome is caused by the intracellular bacterium Xenohaliotis californiensis of the family Rickettsiaceae.

Host range

None of the species of abalone growing wild or presently cultured in Australia has been shown to be susceptible to this disease. However, because five Haliotis species native to the Californian region have been severely affected by withering syndrome, it is assumed that other species of Haliotis may also be susceptible.

Molluscs known to be susceptible to the disease:

* naturally susceptible (other species have been shown to be experimentally susceptible)

Presence in Australia

EXOTIC—not present in Australia.

Epidemiology

• The pathogen Xenohaliotis californiensis occurs in marine waters.
• The bacterium attacks the lining of the digestive tract, apparently obstructing the production of digestive enzymes. Consequently, abalone consume their own body mass, causing 'withering' of the foot, impairing their ability to adhere to rocks and making them vulnerable to predation. Abalone not eaten by predators usually starve to death.
• Susceptibility varies between species of abalone (99 per cent cumulative decline in black abalone and 30 per cent in red abalone since the disease was first observed in 1986).
• Some abalone can be infected with the bacterium without developing the disease.
• Environmental conditions, such as warmer than normal water temperatures, may predispose carriers of the bacterium to disease.

Differential diagnosis

The differential diagnostic table and the list of similar diseases appearing at the bottom of each disease page refer only to the diseases covered by this field guide. Gross signs observed might well be representative of a wider range of diseases not included here. Therefore, these diagnostic aids should not be read as a guide to a definitive diagnosis, but rather as a tool to help identify the listed diseases that most closely account for the gross signs.

Similar diseases

Infection with Perkinsus olseni or Perkinsus marinus

Further images

Sample collection

Because of uncertainty in differentiating diseases using only gross signs, and because some aquatic animal disease agents might pose a risk to humans, you should not try to collect samples unless you have been trained. Instead, you should phone your state or territory hotline number and report your observations. If samples have to be collected, the agency taking the call will advise you on what you need to do. Local or district fisheries/veterinary authorities could advise you on sampling.

Emergency disease hotline

For your state or territory emergency disease hotline number, see Whom to contact if you suspect a disease.

Further reading

www.collabcen.net/toWeb/aq2.asp (not a direct link)

www.pac.dfo-mpo.gc.ca/sci/shelldis/pages/fwsab_e.htm

library.enaca.org/Health/DiseaseLibrary/Disease_card_for_WSA.pdf  PDF

The currently accepted procedures for a conclusive diagnosis of withering syndrome of abalone are summarised at www.oie.int/eng/normes/fmanual/A_00044.htm