There seem to be many infectious agents that have been proposed as being possible etiological agents for Chronic Fatigue Syndrome. None of them have held up specifically as a single causative agent. We'll just have to have to go through the rules of Koch's postulates and see how far we can get. I think it's an interesting candidate for a possible primary agent. I don't think it's an opportunistic infection.
Opportunistic infections are usually airborne and are present everywhere.
They're just waiting for our immune systems to be weakened before they establish a chronic infection. Cryptostrongylus doesn't seem to be ubiquitous. If I'm right about the taxonomy, it looks like it's coming out of a particular geographic area. And they have to do with the wide variety of physiologically active agents roundworms are able to secrete. Well, VIP is involved in regulating blood pressure and blood flow.