The excerpts I posted were from an "uncorrected proof". Perhaps the final version will have different wording. Actually, I thought their conclusions were worthy of notice, regardless of their command of "scientific English". They homed in on the "possibility" that there is a compounding of Nosema C and the assortment of viruses. This idea was recently articulated by Forsgren and Frees

> Our results do not suggest substantial differences in individual level virulence between N. apis and N. ceranae. The high colony level virulence in N. ceranae infected colonies reported from Spain may be a regional phenomenon as high mortality in infected colonies are not always present. Thus, other factors than N. ceranae alone, such as associated virus infections, may be complementary to explain high colony level virulence in this parasite. For example, some viruses, e.g. black queen cell virus (BQCV) and bee virus Y, are known to add to the pathogenic effect of N. apis (Bailey and Ball, 1991).

See: Comparative virulence of Nosema ceranae and Nosema apis in individual European honey bees. Eva Forsgren, Ingemar Fries. Veterinary Parasitology 170 (2010) 212–217

Meanwhile, from a different corner:

> Interactions involving several parasite species (multi-parasitized hosts) or several host species (multi-host parasites) are the rule in nature. Only a few studies have investigated these realistic, but complex, situations from an evolutionary perspective. Consequently, their impact on the evolution of parasite virulence and transmission remains poorly understood. 

> A stumbling point in trying to produce a coherent approach is the terms we use to define this host–parasite complexity. A brief survey of the literature shows that numerous terms, including co-infection, superinfection, mixed infection, concurrent infection, multiple infection, double infection and polyparasitism, have been used to describe the presence of multiple strain or multiple species infections within hosts, sometimes within a single paper.  

See: Parasite and host assemblages: embracing the reality will improve our knowledge of parasite transmission and virulence
Thierry Rigaud, et al. Proc. R. Soc. B published online 28 July 2010

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