Both host genetic potentials for growth and disease resistance, as well as nutrition are known to affect responses of individuals challenged with micro-parasites, but their interactive effects are difficult to predict from experimental studies alone.
The assumption was based on various challenge studies, which showed that food intake reduces with increasing pathogen load until a minimum level is reached that is similar for different levels of infectious dose of micro-parasites [42], [43] and that food intake recovers almost instantaneously when pathogens are removed artificially (eg through drug administration) [47].
The predictions of our model suggest that at higher planes of nutrition improvement in either of these two traits (e.g. by genetic selection) leads to a more effective immune response (seen as resulting low pathogen loads) and higher growth rates respectively, when hosts are exposed to micro-parasites.
Infection starts with the host being infected with a single micro-parasite, which then replicates within the host.
The ability of transmission stages to cause infection and host mortality – and therefore low host survival – is considered an important component of micro-parasite fitness, also in the case of WSSV [8].
Consistent with this hypothesis, many micro-parasites have large gene families that encode surface antigens in sub-telomeric regions (reviewed in [ 54]).
Given the generality of association between surface antigen genes and sub-telomeric regions in micro-parasites, it is interesting to see that T. annulata appears to be an exception to this rule.
Further, epidemiological research on micro-parasitic infection such as malaria is largely based on two distinct measures of parasite abundance within communities of people.
In addition, it is possible that some low abundance viruses may in fact be derived from other eukaryotic organisms present in the host sampled, such as undigested food or prey, gut micro flora, and parasites.
Ticks are parasitic, and some transmit micro-organisms and parasites that can cause diseases in humans, while the saliva of a few species can directly cause tick paralysis if they are not removed within a day or two.
Some of these micro-organisms are parasites of nematodes.
