Host Diversity, Host Range

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Do curso por The Pennsylvania State University

Epidemias - A Dinâmica das Doenças Infecciosas

573 classificações

The Pennsylvania State University

Epidemias - A Dinâmica das Doenças Infecciosas

573 classificações

Not so long ago, it was almost guaranteed that you would die of an infectious disease. In fact, had you been born just 150 years ago, your chances of dying of an infectious disease before you've reached the tender age of 5 would have been extremely high. Since then, science has come a long way in understanding infectious diseases - what they are, how they spread, and how they can be prevented. But diseases like HIV/AIDS, Malaria, Tuberculosis, or the flu are still major killers worldwide, and novel emerging diseases are a constant threat to public health. In addition, the bugs are evolving. Antibiotics, our most potent weapon against bacterial infections, are losing their power because the bacteria are becoming resistant. In this course, we'll explore the major themes of infectious diseases dynamics. After we’ve covered the basics, we'll be looking at the dynamics of the flu, and why we're worried about flu pandemics. We'll be looking at the dynamics of childhood diseases such as measles and whooping cough, which were once considered almost eradicated, but are now making a comeback. We'll explore Malaria, and use it as a case study of the evolution of drug resistance. We'll even be looking at social networks - how diseases can spread from you to your friends to your friends' friends, and so on. And of course we’ll be talking about vaccination too. We’ll also be talking about how mobile phones, social media and crowdsourcing are revolutionizing disease surveillance, giving rise to a new field of digital epidemiology. And yes, we will be talking about Zombies - not human zombies, but zombie ants whose brains are hijacked by an infectious fungus. We're looking forward to having you join us for an exciting course!

Na lição

Basics of Ecology

The third module of the course covers ecological factors that influence the dynamic patterns of infectious disease. We will discuss the conditions under which a pathogen can drive its host to extinction. We will look at how the demography of the host may allow the pathogen to persist in some populations but not others. We will talk about how host and pathogen characteristics interact to shape different temporal patterns of disease incidence at the population level and discuss the ecological consequences of infecting more than one host species.

Pathogens and Host Extinction5:32

Force of Infection5:04

Seasonality3:52

Host Diversity, Host Range3:52

Conheça os instrutores

Dr. Ottar N. Bjornstad
Professor of Entomology and Biology
Department of Biology
Dr. Rachel A. Smith
Associate Professor
Department of Communication Arts & Sciences and Human Development & Family Studies
Dr. Mary L. Poss
Professor of Biology
Department of Biology
Dr. David P. Hughes
Assistant Professor of Entomology and Biology
Department of Biology
Dr. Peter Hudson
Willaman Professor of Biology
Department of Biology
Dr. Matthew Ferrari
Assistant Professor of Biology
Department of Biology
Dr. Andrew Read
Alumni Professor in the Biological Sciences, and Professor of Entomology
Center for Infectious Disease Dynamics
Dr. Marcel Salathé
Assistant Professor of Biology
Department of Biology

Like many consumers in the natural world,

parasites can be either specialists or generalists.

One parasite may simply focus all their attention on one

host species, or alternatively exploit a wide range of host species.

Specialized viruses have the opportunity to really evolve closely with their

host, and a good example would be the human chicken pox virus.

This is an intriguing virus in the

while this is really an airborne childhood disease transmitted by

coughing, can also be transmitted through contact with a rash.

It has evolved a persistence mechanism, which has allows it to

become dormant in the body's nervous tissue, but then will reemerge

when the host is much older and the immunity has waned

at which point it causes the painful disease shingles in adults.

Epidemiologically this is a clever strategy since all the children in an

area recover from the infection and

so carry antibodies preventing subsequent infection, the

virus can still persist, and emerge later when these children become adults

and they can, the adults can then initiate a new epidemic in children.

Another infection of the nervous system that in contrast to chicken

pox will infect does not infect a single host species

but a wide range of host species is the rabies virus.

And this will infect raccoons, skunks, foxes, coyotes, ferrets,

bats, domestic cats, dogs, humans, and many, many other animals.

The infection process at the cellular level for the rabies

virus is similar, similar to many other species, and starts with

the G-protein projections on the virus interact

to the receptors on the host cell surface.

The interesting feature about rabies is the viruses high affinity

for nervous tissue, in particular that it binds to the acetylcholine

receptors, which are not only expressed in high levels of

nerve cells but are also highly consistent between many, many species.

So the way these

virus can infect the nervous system of many different animal species.

On the one hand this provides flexibility, so the

virus has more opportunities to infect different host species.

But alternatively it does not have a within host

presistent mechanism that we just heard about in chicken pox.

So it's the fact that it infects multiple species, allows it to persist.

Instead, it must invade many more species in the

ecosystem, and in so doing attempt to persist over time.

When parasites are driven from a tolerant

host species to a vulnerable host species, then

the more vulnerable host species can actually

be eliminated through parasite mediated, or apparent competition.

A nice example of this is in the United Kingdom, where

American Grey Squir, Squirrels were brought over and released into the

English countryside, and they have wiped out the resident red squirrels.

The reason they've done this is because they both share a pox virus,

but the greys are more tolerant of the pox virus infection than the reds.

So the outcome is that the greys continue to spread the virus

to the reds, and the reds die out, and they've been effectively

been wiped out from most of their distribution.

Quite simply through the effects of the virus as an infective competitive weapon.

This doesn't happen in specialist infections because this is

similar to what has happened in the tolerant species.

Here transmission is dependent on the density of the host population, and

so more hosts get infected when density's high but less when density's low,

such that below the threshold host density the disease effectively fades out.

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