This paper just came out today.  The only thing not mentioned in the 
abstract is: 

"Median survival times of N. apis infected and non-infected bees ranged 
from 18 to 54 days".

This is in sharp contrast to the results with N. ceranae in this study.

Adony

Experimental infection of Apis mellifera honeybees with Nosema ceranae 
(Microsporidia) 
Mariano Higes, Pilar García-Palencia, Raquel Martín-Hernández and Aránzazu 
Meana

Journal of Invertebrate Pathology Vol. 94, Issue 3 , March 2007, Pages 211-
217.

Abstract
In this report, an experimental infection of Apis mellifera by Nosema 
ceranae, a newly reported microsporidian in this host is described. Nosema 
free honeybees were inoculated with 125,000 N. ceranae spores, isolated 
from heavily infected bees. The parasite species was identified by 
amplification and sequencing the SSUrRNA gene of the administered spores. 
Three replicate cages of 20 honeybees each were prepared, along with one 
control cage (n = 20) supplied with sugar syrup only. The infection rate 
was 100% at the dosage administered. The presence of Nosema inside 
ventricular cells was confirmed in the samples using ultrathin sectioning 
and transmission electron microscopy. By day 3 p.i. (post-infection) a few 
cells (4.4% ± 1.2) were observed to be parasitized, whereas by 6 days p.i. 
more than half of the counted cells (66.4% ± 6) showed different parasite 
stages, this value increasing on day 7 p.i. (81.5% ± 14.8). Only one 
control bee died on day 7 p.i. In the infected groups, mortality was not 
observed until day 6 p.i. (66.7% ± 5.6). Total mortality on day 7 p.i. was 
94.1% in the three infected replicates and by day 8 p.i. no infected bee 
was alive. After the infection, the parasites invaded both the tip of 
folds and the basal cells of the epithelium and the autoinfective capacity 
of the spores seemed to spread the infection rapidly between epithelial 
cells. On day 3 p.i., mature spores could be seen inside host cell tissue 
implying that the developmental cycle had been completed. The large number 
of parasitized cells, even the regenerative ones, the presence of 
autoinfective spores and the high mortality rate demonstrate that N. 
ceranae is highly pathogenic to Apis mellifera. Possible relation with bee 
depopulation syndrome is discussed by authors. 

  

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