Manual for Diagnosis of Screw-worm Fly - xcs consulting

8. Surveillance
While SWF remains outside Australia’s borders, the early detection of an incursion provides
the best hope for its subsequent control and eradication. Although the bulk of this manual is
devoted to identification of myiases and the different life stages of SWF, the collection of SWF
material for confirmation of its identity is of paramount importance. The three major activities
in surveillance are: inspections of stock for myiasis and collection of larval samples, the trapping
of adult flies and the collection of egg masses from sentinel animals.
8.1 Specimen collecting from myiases
Agriculture, Fisheries and Forestry - Australia
In cases of suspected SWF myiases, samples of larvae must be taken from the host animal
for identification. Up to 10 larvae should be pulled from the deeper parts of the myiasis with
forceps and put in a sealed container for later processing, or dropped directly into 80 per cent
ethanol. If facilities permit, live larvae can be killed in hot (below boiling) water which causes
them to extend, before putting in formalin or 70-80 per cent ethanol. Alternatively, live larvae
can be fixed by putting into Kahle’s I fixative for up to 24 hours, rinsing in water and storing in
80 per cent ethanol.
To rear out adults from mature larvae removed from host animals, the larvae should be put in
a ventilated container with a small quantity of sand or vermiculite. The larvae will form puparia
within a day and adults emerge approximately one week later, depending on ambient temperatures.
Figure 33: A quarantine warning: Chrysoma bezziana infestation in foot and leg of dog.
Note larvae evacuating wound via the cut pad.
1. Kahle’s: 95% Ethanol (28 ml), 35% Formalin (11 ml), glacial acetic acid (4 ml),
distilled water (57 ml).
53