Hi Jia,

Great question!

I'm a plant pathologist, but facing exactly the same type of interrogation with opportunistic pathogens. Sometimes, the opportunistic pathogens have the ability to exploit tissue once inside, but not to penetrate it unless there is a chance opening ( wounds being the most common ones). Then, the opportunistic pathogens do not have the whole inherent capability to be pathogenic on otherwise 'heathy' hosts. Another situation is organisms that establish as 'secondary infectors' after a previous infection by a 'true' pathogen has weakened the host.

So, to me, opportunistic pathogens are just that - opportunists that take a chance when it comes, but do not entirely depend on it to survive. They are usually necrotrophs in plant pathology. I don't know about human pathogens!

Best regards

Didier

You right Didier, but tell me given the fact that we all know the importance of our immune system and how they function-as in your example the  integrity of the primary immune system; which type of pathogen will survive and establish itself within our body if it doesn't wait for that opportunity for our immune system to fail. I feel that in fact the mere act of an immune response war between pathogens/their agent and our immune system is simply a strategy by the pathogen to create an opportunity for it to establish itself and cause disease within the host. that's my two pence take. Pathogens are opportunistic: but while some wait for the opportunity like TB in the case of HIV/AIDS others create the opportunity and then establish themselves and cause disease.

Hi Jia

I don't think all pathogens are opportunistic. There are true obligate pathogens that can't survive and multiply outrside their host(s), so these need to be infectious to persist. The most classical examples are viruses, which need to use the host cellular machinery to multiply, and often a vector to get inside their host or be transmitted from host to host ( very frequently the case in plant pathology with insect- or nematode- transmitted viruses). These are highly specialised living beings that have evolved to maximise their infectious power, including the possibility to enter the host and avoid immune defense. The only opportunity they do not control entirely is the presence of the host - although some pathogens manipulate the behaviour of infected hosts to maximise the probability of transmission to healthy ones.

There is also abundant work now on the production of effectors by pathogens that weaken or suppress host immune responses. So I would not say that the immunity interplay between hosts and pathogens is a pathogen strategy to create opportunities to infect; I see it rather as a host strategy to reduce the number of opportunities for infection!

All the best

Didier