**1. Introduction**

There are two types of helminths: free-living and parasitic helminths. For decades, free-living helminths have been used as models in studies on mechanisms used to survive against the pathogenic effects of micro pathogens. Because of the evolutionary link between free-living helminth defenses and human innate immunity, this research is highly relevant to humans [1].

On the other hand, little is known about the micro pathogens that affect animal helminth parasites, particularly in the adult form, despite coexisting with large numbers of microorganisms in the intestine of their host. This gap in our understanding is problematic because of the damage that helminth parasites can inflict on the health of their hosts, including humans and livestock.

Identifying the defense mechanism that helminth parasites use against their micro pathogens, as is known for free-living helminths, would be extremely useful. However, this is technically impossible, despite indirect information suggesting that helminth parasites develop defense mechanisms against micro pathogens as a result of the long periods of time they spend inside the intestine of their hosts [2].

One observation relevant to helminth parasites, in relation to the defense mechanisms used by free-living helminths, is that of aerobic organism conditions. Under these conditions, free-living helminths survive against their micro pathogens using in some situations the toxic capacity of the oxygen molecule to induce oxidative stress [3].

The defense mechanisms of helminths against micro pathogens are important in the study of the evolution of helminths from their ancient origins to the modern day. Understanding these mechanisms will provide insights into oxidative mechanisms and reduction-oxidation reactions (redox) more generally, both of which are chemical events present in the defense mechanisms of any pathogen.
