With the low-to-moderate virulence of the strains studied here, the number of deaths due to MDV is very low compared to all-cause mortality regardless of the vaccination status of the birds.
For aerosol challenge an App serovar 7 strain (AP76) was used, as this strain exhibits moderate virulence due to a lack of the cytotoxic and haemolytic Apx toxins I and III.
Verticillium dahliae with moderate virulence can cause the susceptible control (ji11) infection rate of 80%, or a disease index above 50.
In this study we show that different species of Phytophthora have varying degrees of virulence on N. benthamiana ranging from incompatible to moderate virulence through to full aggressiveness.
We found that different species of Phytophthora have varying degrees of virulence on N. benthamiana ranging from avirulence (incompatible interaction) to moderate virulence through to full aggressiveness.
There will be a moderate virulence optimum.
Thus selection would favour a moderate virulence in the parasite towards the predator host.
In contrast, SsMeV showed a relative moderate virulence when mortality and infection probabilities were considered together.
Interestingly LysR proteins are not found in F. tularensis subsp. mediasiatica strains and the absence of LysR proteins in F. tularensis subsp. mediasiatica could be a factor explaining their moderate virulence.
Unlike the preliminary expectation, parasite will not evolve towards reduced virulence, but reach an optimum moderate level of virulence.
