Disease transmission and personality

Thanks Jack and Jonathan for a push to get back in the saddle! Experiments have become manageable again (at least for a short period of time) and Zach and my parents have completed their summer visit. Time for SCIENCE!

Feral_CatOne topic that I find particularly interesting concerns how personality traits influence patterns of disease.  For example, people who are frequently stressed out are at a greater risk of becoming obese or acquiring heart disease. We often look at disease transmission at a population or community level, but I think individual level differences in behavior are a crucial and understudied area of research.

When diseases are transmitted from one individual to another, then social behaviors are an important factor in transmission dynamics. While it’s often difficult to study this phenomenon in humans, numerous social animals provide ideal study systems.

Natoli et al. 2005 is 0ne of the coolest studies that I’ve read on personality traits and disease. This research group examined 3 colonies of feral domestic cats in Europe and collected data on how male personality traits correlated with FIV (feline immunodeficiency virus) infection. According to the article, FIV infections in feral cats are usually lethal within approximately 5 years, at which point the cat’s immune system is too weak to fend off otherwise nonlethal infections.

FIV transmission occurs when one cat bites another, transmitting the virus from its saliva into the other cat’s bloodstream. Bites usually occur when two males are battling over territory or dominance rank or when a male bites a female during sex.

Feral_Cat_2In order to get a handle on the “personality” of the feral cats in each colony, the researchers logged hundreds of hours taking notes on the frequency with which each cat engaged in aggressive, submissive, affiliative, territorial, display or mating behaviors. They aggregated all of these measures and came up for a single score for each individual that indicated how “proactive” or “reactive” that individual was. Proactive cats more regularly marked their territory, were the most aggressive (often winning aggressive interactions) and often affiliated with other members of the colony. Reactive individuals rarely displayed aggressive behavior and were frequently submissive towards other members of the colony.

When the behavioral results were compared with information about which cats were infected with FIV, a clear patterns emerged. The males at the top of the hierarchy (i.e., the most proactive, dominant males) were the most likely to be infected with FIV. Their aggressive demeanor meant that they incurred bites more frequently than more submissive males, increasing the probability that aggressive males contracted the disease.

This finding brings up a logical question. If all of these aggressive cats are contracting terminal diseases, why are aggressive cats still around? Well, the first answer to that question lies in that fact the cats don’t succumb to the illness quickly. The disease has a long asymptomatic period during which the cats continue to strut around as if nothing is wrong.

Importantly, aggressive behavior also maintains access to the ladies. Paternity tests revealed that the proactive cats were fathering a lot more of the kittens than the reactive males. Because aggressive dads produce more offspring than submissive dads, we might not expect aggressive behavior to be diminishing anytime soon.

This was a particularly nice study because it examined multiple populations (lending support to the generality of the results), measured lots of behaviors and included a direct measure of evolutionary fitness. It’s rare to find so comprehensive a study.

When dealing with socially transmitted diseases, personality plays a large role in the number of times an individual may be exposed to an infectious agent. In the study described above, aggressive behavior was the key to transmission. In other systems the important relevant measures may be frequency of sexual behavior, energy put into hygiene, number of individuals with which one associates, etc. Personality plays a large role in determining the diseases to which one is most susceptible.


4 thoughts on “Disease transmission and personality

  1. While I understand the point made here, it seems a little bit obvious. It’s like saying that people who have lots of unprotected sex with other loose people are more likely get an STD than someone with less of a sex drive.
    Finding a correlation between the factors in the study and the contraction of diseases by purely internal functions would have been quite interesting.

    Either way, glad to see more posts.

  2. Actually, there’s an interesting corollary study (which of course I can’t find a link to) that looks at how the human immune system (specifically in men) is affected by muscle mass. It seems that men with greater muscle mass have measurably weaker immune systems, as the body sacrifices energy from vital systems to improve the (ostensibly more superficial) musculo-skeletal system.

    Ostensibly this has an evolutionary advantage in that the stronger, more attractive men have a greater chance of having more offspring, and as a result are more successful genetically. However, there seems to be a fail-safe, if you will, because the stronger immune systems of the “less attractive” (i.e. me :P) men make it more likely they will survive any bouts of plague and so forth. This leads to a longer time in which to have children (longer life span), so they get their chances as well (hypothetically speaking). And of course evolution didn’t take into account things like, oh, agriculture, modern medicine, anything technologically speaking that humans developed in the last 10,000 years, so this probably isn’t as obviously represented in the general populace anymore.

    Of course women get the best deal – they have a significantly stronger immune system, a much sturdier bone structure, mature much faster, have higher rates of intelligence, are more capable of succeeding with poor nutrition and access to resources, live much longer, and have a much greater chance of passing on their genes to children (as women are far more likely to be reproductively successful.) Take that feminist theories of the repressive patriarchy – biologically and evolutionarily, women win every time.

    For obvious ethical and moral reasons, it would be wrong to raise human children in a feral environment. But it would still be an interesting hypothetical scenario. Too bad we don’t have an isolated pocket of completely undeveloped hunter-gatherers to observe easily. (Easily being the key word, as groups in the amazon and other isolated regions are generally pretty difficult to access.)

    Anyways, thank you for returning with yet another fascinating topic!

  3. Liked the article. I worked with a lot of cats when I was Italy once, Pisa area, and the FIV infection rate was absolutely staggering. Tons of ferals stalking everywhere, almost all infected.

    Oh and welcome back 😀

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s