My guess is that, if given a healthy biological population (many individuals and high genetic diversity), a novel parasite could only do limited damage before that population adapted to its ill effects and mitigated them. After all, a parasite's goal isn't to kill its host, just to profit from it. Otherwise the parasite could very well go extinct too!

However, there a many examples today of very unhealthy populations. All it would take would be an inter-species parasite, such as a virus or bacterium, to gain a foothold and wipe out what remains of the population. Given the timescales we are dealing with, it must have happened before (though I can cite no examples). But would you consider the extinction itself to be caused by the parasite, or the events that led to the population bottleneck in the first place?

Causation is a funny thing.

My guess is that, if given a healthy biological population (many individuals and high genetic diversity), a novel parasite could only do limited damage before that population adapted to its ill effects and mitigated them. After all, a parasite's goal isn't to kill its host, just to profit from it. Otherwise the parasite could very well go extinct too!

However, there a many examples today of very unhealthy populations. All it would take would be an inter-species parasite, such as a virus or bacterium, to gain a foothold and wipe out what remains of the population. Given the timescales we are dealing with, it must have happened before (though I can cite no examples). But would you consider the extinction itself to be caused by the parasite, or the events that led to the population bottleneck in the first place?

Causation is a funny thing.

This is a good question, Ajit. An item that comes immediately to mind and I don't know if you would classify the Verroa Mite as a parasite to the Honey Bee, but I consider it so, as it is weakening the Honey Bee Population worldwide. A researcher who noted this trend about 10-12 years ago noted to me that he thought it was a GMO-spawned species that was coming out of the United States and Brazil at the time, but have not seen anything conclusive on that. But as it stands now I believe the Honey Bee population is down about 80-802% worldwide, which as you know as the principal pollinators could bring us serious famine in many nations.

Your point about bees is a good one Max, because it brings up an important aspect of parasite transmission: population density. Populations that form colonies of closely related individuals must be much more susceptible to parasite transmission. This includes insects like bees and ants, but also many mammal species like naked mole rats, bats, and humans. One of the major factors cited for the high mortality rate of Bubonic Plague in Europe was the high-density urban environments where the disease could easily jump from one host to another.

In North America, scientists are witnessing the in-progress implosion of cave-dwelling bat populations thought to be due to White Nose Syndrome, caused by a fungus that infects many species of bats and kills them during their hibernation (I believe that's accurate). It has such an easy time with transmission because the bats huddle together while they roost. It isn't known how the fungus spreads between caves, but humans, and especially scientists studying bats are implicated as vectors.

Entire cave systems in the Central and Northeastern United States are completely empty as a result of this parasite, and it's believed to be spreading.

http://en.wikipedia.org/wiki/White_nose_syndrome

You know the bat-white noise-fungus phenomena might bear some commonality with the Bubonic Plagues of Europe in terms of weakened immunology. On one of my trips to UK some years ago, an Oxford scholar told me the devastation of the Plague would have been a fraction of what it without the fact that lead levels were extremely high from the orient into the Mediterranian into inland and coastal Europe into Scandinavia. Some had supposed that the density rule was the reason that rural areas did not experience much loss compared to cities like London and Rome. But he said it was the lead-lined water system, the pewter jewelry, and pewter everything household (utensils, cookware and dinnerware)--couple that with lead and mercury so prevalent in the hats and clothing of the more affulent of the day--and then he mentioned that just a few miles outside London were Jewish villages that dipped their water from wells, wore almost no jewelry (certainly not pewter) and used wooden utensils and dinnerware and cast iron cookware--very little lead exposure to weaken immune systems) and their men would trek daily into London to bury the dead that the city men were either too sick to bury or would not go near them. In the process, when the Jewish men did not catch the Plague the city folk--the recipients of their goodwill--would turn against the Jewish people, declaring them as witches that had put a spell on everyone else, since they seemed immune to the Plague. I mention this example also because what we are seeing with the Honey Bee population is a general decline in immunology as the Mites have grown stronger and have been virtually impossible to irradicate by conventional insecticides without destroying the host Bees, also.

When we look the exponential rise of parasitic growths in (candida or psoriasis, for instance) in humans today we note that these progress only in acidosis states--hence, falling cellular pH in the population as its diet consists increasingly of "dead" food (irradiated, microwaved, processed, indefinite shelf-life, synthetic fortification). In this vein we have seen pandemic growth in diabetes mellitus type 2, cancer of all kinds, and CVD. A population that is slowly starving for organic nutrients as they eat more and more calories without benefit of even satiation. So the mitochondrial integrity of the cells seem compromised in the average American--and the medical response is to leave the cellular environment and its dietary drivers as is while attacking the offending organisms and metabolic decline. Not very effective; in fact introducing a whole new set of pathologies induced by polypharmacy and myriad surgeries and artificial prostheses that make matters worse in too many cases.

I understand the unhealthy populations mentioned by Alexander Devaux are of low genetic diversity and ecologically constrained, and are more prone to destruction by parasites of extreme virulence and broad host range. Theoretical possibility exists that founder populations following bottlenecks become targets of highly virulent parasites leading to extinction of the host species.

Verroa destructor has decimated honey bee populations as pointed out by Max. I am aware of some studies showing association of viruses, bacteria or fungus with Verroa for causing the overall damage. I do not know whether honey bee has reached its bottleneck.

It would be interesting to see advances in development of 'model(s)' by population geneticists to explain and predict 'parasite-driven' extinction of host species.

Cunningham, A. A. and P. Daszak (1998). "Extinction of a species of land snail due to infection with a microsporidian parasite." Conservation Biology 12(5): 1139-1141.

As previously mentioned, the key mechanism stopping a parasite causing the extinction of a host species is density-dependent transmission - as the density of a host reduces, parasite transmission rate drops, hence parasite abundance also drops. If however there is a populous reservoir host for the parasite, parasite abundance may remain high, potentially causing extinction (see parasite-mediated apparent competition). A good example is the introduced grey squirrel in the UK, the native red squirrel, and the parapox virus which infects both. The red squirrel appears to be heading towards extinction in the UK and the virus may be the main cause.

Amphibian - fungus Batrachochytrium

Thank you Andrew and Alex for citing good examples of parasites as causes of extinction of the host species. But honestly, I was curious to know about parasites that could have caused extinction in its strict sense- as marked by the death of the last surviving individual of the host species in the total space/ecosystems on earth. The subject matter is inherently complex and it is probably difficult to prove the global absence individuals of the species- if it so small as an amphibian or snail. Taxonomy presents its own problems. Local extinctions expanding into trans-continental dimensions might give semblance of global extinction!

Parasite-driven extinction of host species (vertebrate host species) seems to be highly improbable due to the elaborate immune system of host with Ir (immune responsiveness) phenomenon controlled by MHC and non-MHC loci. There should always be co-existing highly susceptible and highly resistant individuals in a population of any species presenting a spectrum of defence at 'herd' and species level. I think immunologists strongly tend to believe in that.

There is a nice review precisely on that topic:

de Castro, F. & Bolker, B. M. Mechanisms of disease-induced extinction. Ecology Letters 8, 117–126 (2005).

THE ROLE OF TREMATODE INFESTATION IN THE SPECIFICS OF SKELETON MORPHOGENESIS OF RANA ARVALIS NILSSON, 1842

Vershinin V.L., Neustroeva N.S.

Doklady Biological Sciences. 2011. Т. 440. № 1. С. 290-292.

I fully agree with Francisco- it is an excellent effort to compile and present the subject as we have understood. Thanks for educating me on the issue. Your review describes the extinction of land snail (paper cited above by Andrew Stringer)-elimination of the last survivors in captivity- an example of human intervention. A biological species (Homo sapiens) interacting with others to domesticate some and to threaten others definitely has carved its unique niche. I would like to be forgiven for a bit more digression from the topic.

Hi Ajit,

I think it is certainly possible that disease could lead to sufficient reductions in host population size that other factors could "finish off" the population. A very good reference on this subject was published recently by Hamish Mccallum:

https://www.researchgate.net/publication/230830641_Disease_and_the_dynamics_of_extinction?ev=prf_pub

Definitely worth a read!

Cheers,

Nick

Article Disease and the dynamics of extinction

Dear All,

The aim of a parasite or a parasitoid has never been to extinct its host. Regarding the special literature in most cases the population dynamics of parasites and host show a relationship described by the Lotka-Volterra equations. Parasites or predators using them as biological control agents have been often very efficient but have not destroyed the host population.

As to the lead and plagues relationship thorough weakening the immune system may be only a hypothesis difficult to prove scientifically. Max’s example with the Jewish population cannot be significant because their number was very low to the Christian population and traditionally they lived in isolation. I note even the hygiene of Jewish people was more developed than that of the Christian population because the later avoided washing their hands and bodies but in case of Jews there were ritual toilet (purity) rules like the mikveh

http://en.wikipedia.org/wiki/Mikveh

http://en.wikipedia.org/wiki/Ritual_purification

I would ask what about the impact of plague on Jewish populations in other parts of Europe?

„Long-term coevolution sometimes leads to a relatively stable relationship tending to commensalism or mutualism, as, all else being equal, it is in the evolutionary interest of the parasite that its host thrives. A parasite may evolve to become less harmful for its host or a host may evolve to cope with the unavoidable presence of a parasite—to the point that the parasite's absence causes the host harm.”

References:

Price, P.W. 1980. Evolutionary Biology of Parasites. Princeton University Press, Princeton

Lively CM, Dybdahl MF (2000). "Parasite adaptation to locally common host genotypes". Nature 405 (6787): 679–81. doi:10.1038/35015069. PMID 10864323

Rook GA (2007). "The hygiene hypothesis and the increasing prevalence of chronic inflammatory disorders". Transactions of the Royal Society of Tropical Medicine and Hygiene 101 (11): 1072–4. doi:10.1016/j.trstmh.2007.05.014. PMID 17619029.

I remark: In a scientific community participants do argue and not anonymously down-vote!

I agree with Andras--I could not imagine anyone having a reason to downvote responses to a topic like this. True scholars, like he said, argue the points, raise constructs and theories to consider, and otherwise, maintain courtesy in their interchanges with colleagues. None of us are so superior as to have all the answers, and as the knowledge base expands we find we have far fewer answers to the problems that beset mankind than we thought we did. I appreciate all commenters on this topic.

I was just entering this interesting question. And to be honest, I can´t imaging any mechanism, which could prevent the extension of the host of parasites. If this would be possible, some kind of discernment has to exist. Can one of the specialist help me against my ignorance?