bad infection with microsporidia
Michael Ashburner (Genetics)
ma11 at gen.cam.ac.uk
Sun Jul 11 11:04:29 EST 2004
Poor you - no, there is not much in the Greybook. There is a bit, but not much, more
for the new edition (which we hope will be published in November). I have extracted
what there is below. If anyone has any further information on how to deal with these
serious nuisances please let me know.
And Slawek - PLEASE do NOT send out any flies from yr lab until this is cured !
Once considered to be amitochondriate protists, microsporidia are now known to be more closely related to the fungi
(Hirt et al. 1999). Microsporidia are obligate intracellular parasites. Microsporidian infections are a potential
threat to the laboratory culture of Drosophila, and, in view of the extensive and damaging association of these organisms
and insects in general, it is perhaps surprising how rarely they have been a problem. Stalker and colleagues (Wolfson et al. 1957;
Stalker and Carson 1963) have drawn attention to the dangers of microsporidian infection; however, one of the organisms they found
is now thought to have been a fungus (Lushbaugh et al. 1976; see 38B /7.1).
Most of our knowledge of microsporidia infection of Drosophila is of Nosema kingi Kramer, described from an infection of D.
willistoni discovered by Burnett and King (1962) (Kramer 1964b). Infection appears to be largely asymptomatic, although infected D.
melanogaster have a reduced adult life span (from a mean of 35.3 days in uninfected flies to one of 28.3 days in infected flies)
(Armstrong et al. 1986), prolonged development, some pupal mortality (Armstrong and Bass 1988), and reduced fertility and fecundit
(Armstrong and Bass 1989). N. kingi has also been found in laboratory cultures of D. melanogaster in California (Armstrong et al. 1986)
and in D. simulans (Comendador et al. 1986). These microsporidia can be transmitted between flies both orally and, at a relatively low
frequency, transovarially (Armstrong et al. 1987). According to Armstrong (1977), artificially infected males and females will only
transmit N. kingi to their progeny when crossed to uninfected mates more than three weeks after infection, presumably the time required
for the microsporidian to invade the reproductive system.
Thomson (1960) and Kramer (1964a) discuss other reports of the infection of Drosophila by microsporidia (Chatton and Krempf 1911;
Bell 1953) and note that Octosporea muscaedomesticae Flu, which as its name suggests infects houseflies, and O. monospora Chatton and
Krempf can also infect Drosophila (see also Kramer 1973). The site of infection of O. muscaedomesticae is the gut, which, in Phormia at
least, becomes swollen and milky white in appearance. This species has long narrow spores (5.4-7.4 B5m x 1.8-2.4 B5m) (the spores of N.
kingi are about 4.2 B5m x 2.5 B5m when fresh and 3-4 B5m x 2 B5m after staining; Armstrong et al. 1986). The spores of microsporidia include a
remarkable structure known as the polar tube; when the spore is activated this tube discharges explosively from the spore and penetrates a
nearby cell, into which the sporoplasm if transferred. Probably the most reliable and easy way of diagnosing a microsporidial infection
would now be by PCR amplification of ribosomal RNA sequences using microsporidial specific primers (vide Hogg et al. 2002).
Microsporidia infect all of the major internal organs of flies, including the gonads. They may be recognized by the presence of
spores, and according to Bell (1953), infected adults have swollen abdomens. The spores are not, apparently, resistant to desiccation
(Wieser 1963). Transmission may be either by feeding on infected food or transovarially. Armstrong (1976) eliminated Nosema kingi from
infected D. willistoni by feeding either fumagillin (at 0.25-8.0 g/liter in sucrose) or Benomyl (at 0.25-0.5 g/liter in sucrose) to
adults. Fumagillin (2,4,6,8-decatetraenedioic acid, mono[5-methoxy-4-[2-methyl-3-(3-methyl-2-butenyl)oxyranyl]-1-oxaspirol[2,5]oct-6-
yl]ester), a product of Aspergillus fumigatus, which may be marketed as the water-soluble Fumidil-B, is used for the control of N. apis in
honey bee colonies (and for the treatment of intestinal microsporidial infections in humans); it is active against the vegetative stage
of Nosema, not the spores. That said, these drugs are a quite toxic to flies, at 8g/l Fumagilin-B (another soluble formulation of
fumagillin, MEDVET Pharmaceuticals, Alberta, Canada) resulted in considerable mortality and, in of itself, was insufficient to eliminate a
serious infection in Toronto; other actions, such as rapidly expanding stocks and dechorionating embryos, were also necessary (G.L.
Boulianne, pers. comm.). Comendador et al. (1986) freed a strain of D. simulans from N. kingi by culture at 17oC, rather than at 25oC, for a "few" generations.
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