Factors affecting horizontal transmission of the microsporidium Amblyospora albifasciati to its intermediate copepod host Mesocyclops annulatus.

MICIELI, M. V.; GARCÍA, JUAN JOSÉ; ANDREADIS, THEODORE G.

JOURNAL OF INVERTEBRATE PATHOLOGY

ACADEMIC PRESS INC ELSEVIER SCIENCE

Año: 2009 vol. 101 p. 228 - 233

0022-2011

Factors involved in horizontal transmission of the microsporidian Amblyospora albifasciati to its intermediate copepod host, Mesocyclops annulatus were examined in laboratory bioassays in relation to life history strategies that facilitate persistence of the microsporidium in natural populations of its definitive mosquito host, Ochlerotatus albifasciatus.  A moderately high quantity of meiospores from mosquito larvae was required to infect copepods; the IC50 was estimated at 3.6 x 10 4 meiospores/ml thus denoting that relatively large concentrations of spores are likely required to infect field populations.  Meiospore infectivity following storage at 25ºC was detected up to 30 days, while meiospores stored at 4ºC remained infectious to copepods for 17 months with virtually no decline in infectivity, demonstrating that meiospores of A. albifasciati are relatively long-lived and can remain viable for prolonged periods in the aquatic environment outside of the host.  Uninfected adult M. annulatus are long-lived; no appreciable mortality was observed in field-collected individuals that were held at 25 oC up for 26 days, with a few individuals surviving as long as 70 days.  The pathological impact of A. albifasciati infection on M. annulatus resulted in a 30% reduction in survivorship after 7 days followed by gradual progressive mortality over a period of several weeks with no infected individuals surviving more than 40 days.  This moderate level of pathogenicity allows for a steady continual release of an inoculum of infectious spores into the aquatic environment where they may be ingested by developing mosquito larvae.  Infected copepods were shown to survive in sediment under conditions of desiccation up to 30 days, thus demonstrating their capacity to function as an effective link for maintaining A. albifasciati between mosquito generations following periods of desiccation.  The susceptibility of late stage copepodid M. annulatus to meiospores of A. albifasciati and subsequent transstadial transmission of infection to adult females with no apparent pathology was established, but we were unable to demonstrate transstadial transmission of infection to any adult males, consistent with the established site of A. albifasciati infection in the copepod host, ovarian tissue.