Monday, January 28, 2008

*** Riddled with Life by Marlene Zuk

This book is an excellent complement to "Survival of the Sickest" making it clear that we have co-evolved with life's oldest members - bacteria, viruses, and parasites. And as we face this fact, it challenges our notion of disease, and who we are exactly. Many thought provoking passages.

Is sex sick?
The need for sex can be laid at the feet of pathogens, which cleaved us from an early evolutionary asexual stage (think cloning or budding) into 2 sexes, with all the turmoil that followed. Disease has gone onto influence how we choose our mates, how we produce and protect our children, the reason we distrust strangers. We may be attracted to each other because we see, however unconsciously, a partner who would be more resistant to disease. P5

You'd think you're back would stop hurting after 4M years
The evolution of bipedalism, thought to have arisen over 4M years ago, may have freed humanity’s hands, but it also caused a shock to the skeletal system from which we have still not recovered. Anthropologists speculate that our joints would have to be too large for efficient locomotion if they were also stable enough to bear our body weight, resulting in the current compromise of aching backs and knee braces. P15

The Nobel Prize winning breakthrough for treating syphilis patients came in 1927 when Austrian Julius Jauregg deliberately infected patients with malaria to induce high fevers; most of the patients showed striking disease remission; where upon he cured the malaria with quinine… More recently malaria therapy has been proposed for Lyme disease. P18
Rabbits can lower the number of disease causing bacteria in their systems more easily if they develop a fever. Goats infected with a parasite and then given a fever reducing drug died, while those left untreated had a mild infection and recovered… Artificially lowering body temperature seems to interfere with the ability to fight off a variety of infections… Fever may be a helpful, adaptive response of the body to illness, not the menace it became known as in the last century. P21

So why are we so deathly afraid of fever then?
19th century experiments on lab animals were demonstrating high temperatures as heatstroke, not fever. True fevers involve a recalibration of the body’s internal thermostat, so that instead of keeping 98.6, the new set point is 101. Which is why sitting in a sauna is not the same as having a fever. P21

If fever helps our immune system, why aren't we always feverish?
Fever is metabolically quite costly, requiring extra energy that must be extracted from food to create this heat, rather than being used for a multitude of other activities… Some scientists have speculated that lower temperatures stave off aging by reducing the amount of toxic materials produced by the cells during an immune response, making it best to maintain the lowest possible temperature as we can. P22

WHO really knows the facts about fever
WHO (World Health Org) came to a rather startling conclusion after studying the research on fevers in children; fever reducing drugs in children made no difference in the outcome of the disease, the duration of the symptoms, or even the comfort level... Medical researchers have also debunked 2 common misconceptions about high fever in children: that it results in seizures, and that fevers must be controlled before they reach 106 to prevent brain damage… While it is true that temperatures of 106 are potentially damaging, such temperatures are virtually always the result of heatstroke or brain injury not infection, and so fears of a cold or flu caused fever rising to this level are groundless… WHO states “The principle rationale for fever reducing therapy is to soothe worried parents and to give them the sense that they are controlling the child’s illness.” P23

So is it feed a flu, starve a cold or vice versa? Well, how about neither.
Reduced appetite during sickness may be linked to a mechanism for eliminating virus infected cells…Apoptosis targets cells that are already infected with virus particles. Food restriction makes this process happen more easily… It is possible that the mild loss of appetite associated with illness is therapeutic. P24

The one way switch is now broken
The more body fat a person has, the more leptin he produces, and leptin reduces appetite. But administering leptin to obese people doesn’t help much, and in fact these people already have high levels of leptin relative to thin people. So what if appetite is stimulated by low leptin levels. Recognizing obesity simply wasn’t necessary in most of our evolutionary past. P25 What’s going on? Perhaps the leptin system was built to only help us in one direction – to encourage us to eat more not to eat less. Think about it, evolution has not had to deal with a modern situation of 10,000 calories available to you in your fridge 24/7

Cystic Fibrosis to the rescue
CF is not a disease but an evolutionary adaptation to cholera and other diarrhea inducing illness. Having a single CF gene (you need 2 copies to be disease stricken) showed that you secreted far less fluid than normal. Researchers suggested that humans with 1 copy would have been at an advantage when cholera epidemics struck. P35

How to raise allergy free children? Throw them in the pigpen!
Having older siblings is particularly likely to be associated with decreased incidence of asthma and allergies, as is the presence of a pet when a child is born. Rural children are also less affected. P41

How did we come up with this [lack of] hygiene hypothesis?
In 1989, researchers theorized that lower standards of living, poor healthcare system, and more polluted environment of East Germany would cause a higher rate of disease than the cleaner West. The opposite turned out to be for children, with children from the East being much less likely to suffer from allergies and asthma… The hygiene hypothesis suggests that diseases such as asthma and allergies arise from an environment that is too clean, so that the normal stimulation of the immune system during infancy is missing, impairing its ability to respond normally to actual pathogens but ignore harmless entities like pollen… Researchers have noted that in areas where malaria is rampant, people suffer from far fewer autoimmune diseases… The rate of hayfever is lower where the rate of TB is higher… Italians who have been exposed to Hepatitis or other parasites were less likely to suffer from asthma or hayfever… African children from Gabon were 32 times less likely to suffer skin allergies to dust mites. Even the lowly cold is associated with reduced incidence of wheezing caused by asthma. Several doctors have quipped “the cure is the common cold!” p43

Are we vaccinating ourselves into a society of asthmatics?
The immune system has killer T cells and helper T cells. The helper T cells come in 2 types Th1 and Th2. Th1 is concerned with bacterial and viral diseases, and Th2 with worms and parasites… In countries with scrupulous hygiene, where children are vaccinated and antibiotics are widely administered, the low level of Th1 stimulation results in an increase in the Th2 response. These exaggerated Th2 responses produce mucous and constrict airway muscles, leading to allergies and asthma. In countries without vaccination and antibiotics, the Th2 responses are activated, but they are regulated by repeated cycles of infection and inflammation, with the inflammation countered by natural anti-allergic reactions… The immune system still respond to pollen or dust mites, but it as if the Th2 arm learns to recognize an innocuous foreign substance for what it is, and has a ‘been there, done it’ reaction, rather than spiraling out of control in a cycle of swollen tissue and drippy glands. P47

Take 2 worms and call me in the morning
Wherever there is deworming you are seeing a rapid rise in inflammatory bowel disease frequency. The worms are thought to stimulate the Th2 response, which then helps to regulate Th1 activity. A malfunctioning Th1 response is characteristic of Crohn’s disease… 4 Crohn’s sufferers were infected with worms, 3 achieved remission, and the 4th showed marked improvement. Not one showed a single side effect, unlike conventional drugs… A study of 29 patients suffering colitis who were entered into a 12 week double blind experiment using worms for treatment. About ½ of the people ingesting worms showed significant improvement vs. 15% of the placebo control group. P52

Think eating worms is gross? Well think about this…
Half the weight of your stool is living bacteria. What are a few worms more or less? P53

Mice reared in a germ free environment must consume 30% more calories to maintain the same weight as conventional bacteria ridden mice. P56

Diarrhea can be ameliorated or prevented by administering a dose of good bacteria (lactobacillus and bifidobacterium) called probiotics. P57

A sampling of microorganisms on tortillas purchased from gloved or barehanded servers. Thankfully, few of the tortillas were contaminated with many bacteria, but if anything, the ones from gloved workers were more likely to harbor germs. The problem is that one almost always contaminates gloves when putting them on. P63

It takes the body several days to generate the targeted antibodies for a particular infection. If a pathogen could change its appearance during this brief period, it could maintain a higher level of virulence. Evidence of this is seen in the parasite that causes sleeping sickness. Its protein coat can undergo many 1000s of alterations in a few days, effectively eluding the immune system. P80

Did parasites cause us to have sex?
Genetic recombination is the mixing of genes. One possibility is that this recombination fostered by sex evolved to clear out the mutations that accumulate when DNA replicates asexually. Because genes realign on their chromosomes every time a male makes sperm or a female makes eggs, the number of mutations diminishes. P89

The reasoning went, that with sex, evolution could proceed more rapidly and species could change more readily as well… But the need for fast evolution isn’t a good explanation for sex for 2 reasons. First, changing rapidly as the epochs go by doesn’t make a species more likely to succeed; plenty of organisms look just like they did eons ago. Second, is that it relies on a benefit for the species not an individual. These good for group arguments don’t work evolutionarily… Which would you rather have 20 lottery tickets with the same number or 10 with different numbers? So producing variable offspring could be beneficial even if those offspring are fewer in number. This sounds fine, but it falls apart under closer examination. The disadvantages of sex are just too large to be offset by a chance at winning in a random draw if what produces the winning ticket is left to chance. Imagine that one lucky offspring is blessed with ‘right’ genes for a specific environment. Those genes can be passed on to others sexually, but they will be watered down with sexual recombination. But you need many such lottery winners, not just one, and further more they have to be appropriate age and sex to repopulate the environment. Sure it could happen, but there is no evidence that it does. And even if sex gave you an initial edge over the environment, it would need to do that again, because the environment does evolve back at you. The biological environment does however… Because natural selection acts on both parasite and host, any adaptation that makes an animal better at resisting will be met with a counteradaptation. Host-parasite interactions provide the constant pressure to reinvent oneself: the perfect inspiration for sex. P92

Think you're a tough guy huh?
Human males who wish they could last longer may be daunted to learn that many insects copulate for hours or even days. Stink bugs mate for 10 hours, golden egg bugs copulate for up to 2 days, and a type of stick insect has been clocked at 79 days. P107

If STDs are harmful, and having more sex partners – at least infected one – increases the likelihood of getting one, it is logical to conclude that natural selection should act on hosts to reduce the risk of transmission by affecting the way hosts mate… First it is reasonable to assume that a high prevalence of STDs would make animals less promiscuous… Second, animals should attempt to discriminate among potential mates and refuse those that appear infected. It turns out that neither of these is borne out in nature. Why? Short term gains can offset long term losses, so while STDs increase with the number of partners, individuals who reduce their partners are simply outreproduced by those who do not. P111

Highly attractive males are also the most likely to be infected, simply because they are doing the most mating. If the choice is between a loser without disease or a superstar potentially infected, females are still likely to benefit by choosing the latter. P114

Is maleness a fatal disease?
Being male is now the single largest demographic risk factor for early mortality in developed countries… Females don’t just live longer, the suffer from less disease. P126

The physiological explanation has it roots in a little known side effect of the very substance that makes males: testosterone… The hormone can depress the ability of immune cells, tissues, and organs to devlop… More indirectly, testosterone can cause levels of cortisol (stress hormone) to increase, which further suppresses the immune system. P130

The only entire class of disease that is generally more severe in women than men are autoimmune disorders in which the immune system is too vigilant… Women seem to produce more T cells. P131

Male ornamentation is a signal of immune health - that explains a lot.
Turkey breeders (and turkey hens) can look at the comb of males and diagnose TB if these parts are bluish, or if the wattles are swollen then cholera can be diagnosed… The degree to which a species is plagued with parasites should mirror the degree of flamboyance its males must evolve. Therefore peacocks should have more than wrens. P150

Polygyny is more common where populations are plagued by diseases such as malaria, sleeping sickness, and worms… Could the heavier parasite burden lead to higher degrees of sexual selection and hence polygny? P161

What would happen if a male cheated – produced a big display without having the good immune genes to back it up? Here is where testosterone comes in. If it is necessary for the production of the secondary sexual characteristics (showy plumage, etc.), but also increases their vulnerability to disease, only those males of particularly high quality would be able to maintain showy ornaments despite the onslaught on their immune systems. P164

It is logical to suggest that animals with sexual ornaments that carotenoids (colors from plants) for their showy colors are therefore signaling both their foraging ability and their health with those ornaments. P182

Even baby animals signal with carotenoids to demonstrate their vigor… Parents dole out their affections unequally, and those chicks with the brightest colors – indicating the greatest health – get the lion’s share of attention and food. P185

Think twice before eating that piece of sushi
With the increase popularity of sushi worldwide, infections of Anisakis worm are on the rise (2000 per year globally with most case in Japan, but the US and Europe come in for their share not only from sushi but smoked salmon, pickled herring, and other uncooked fish). The parasite has to be removed surgically or via a tube inserted into the throat, since drugs are ineffectual. P215

It's a small wormy world after all
More than 1/3 of the world’s population has one kind of worm or another… Virtually all of th'ese infections are due to man’s ineffective insulation from his own excrement. P217

Although saliva is not a completely effective antibacterial agent, it is still helpful in controlling infection, which suggests that concerns about keeping pets or people from licking or sucking on a wound may be misplaced. P224

Humans across all societies show a distrust of newcomers or those who appear different from their usual social group, and several scientists have suggested that xenophobia evolved as an aid to avoiding disease... Certainly, shunning unfamiliar individuals keeps them from infecting you with plague, but it also has a myriad of other functions, and it is difficult to say the least to rule out causes other than disease avoidance for being suspicious of strangers. P226

Disgust at the sight of blood, pus, feces, and vomit evolved as a means to protect us from becoming infected. P226

Strangers are perceived as more disgusting. A survey of 40,000 asked them to choose whom they would least like to share a toothbrush with. Best friends and spouses were most preferred, followed by bosses and coworkers, the TV weatherman, and last the postman… Why in the world are people more comfortable with the weatherman over the postman? The power of TV to forge bonds with our Paleolithic brains. P228

Women’s perception of what is disgusting during pregnancy changes. Immunity is low during the first trimester, as the woman’s body grows to accept the fetus as part of her self rather than an invader… Even after taking the women’s nausea from morning sickness (which is also related to bodies sensitivities to plant toxins – see Margie Profit) into account, disgust levels were highest during the 1st trimester. P229

Here’s an oxymoron: A creationist with drug resistant staph.
If you do something to bacteria, bacteria will do something back to you. Antibiotic resistance is nothing more than evolution by natural selection. P244

Simple soap and alcohol based cleaners kill bacteria without containing antibiotics and without causing problems like the evolution of resistance. Unlike antibiotics which target specific elements of the bacterial structure, soap binds indiscriminately to the bacterial cells allowing them to be washed away. It easy for the bacteria to evolve resistance to a substance with narrow objectives and much harder to evolve resistance to a generalized foe. Also, soap & water or bleach or ammonia cleaners don’t linger on surfaces the way that antibiotics cleansers do, which means there is less danger of killing off innocuous bacteria as well. P247

Is cancer contagious?
Some scientists believe that the sheer magnitude of chronic diseases like cancer and heart disease argues for their infectious cause. The notion that a large proportion of the population would perpetually suffer from a disease that reduced the likelihood of reproduction to be simply implausible… Even a small reduction in the number of offspring an individual has can result in eventual elimination of that individual’s genes. Although diseases that strike late in life will have a smaller effect than those that cut off an individual’s reproduction at the start. Further, humans spend so much of their lives contributing to their children and grandchildren, anything that causes earlier death or disability will be costly…. Furthermore, studies of identical twins, who have the same genes, rarely show that the illness occurs in both members, as would be expected if genes dictate the ailment. P263

[Scientists] believe that schizophrenia is the perfect candidate to have an infectious cause, given the low reproductive rates of schizophrenics… Evolution should have knocked out the genes associated with schizophrenia years ago, since it carries such a high cost… In temperate climates, schizophrenics tend to be born in late winter or early spring, when stillbirths, often caused by prenatal infection, are also at their highest. This argues for schizophrenia being an infection that the mother contracted during early pregnancy and suggests that the culprit is something she is more likely to be in contact with when she spends time indoors… The strongest candidate to date appears to be toxoplasmosis because if a female mammal is infected during pregnancy it can also damage the central nervous system of her fetus. Pregnant women are already urged not to come in contact with cat feces. Children of mothers who were infected during pregnancy show higher levels of mental retardation and seizures. Why the seasonality? The mothers were more likely to be exposed while indoors during certain times of the year… Using a huge sample of mothers from 1959 to 67, researchers found that if a mother had high levels of the antibody [for toxoplasmosis], indicating prior infection, her child was more than twice as likely to become schizophrenic as compared to a child from a mother who tested negative for the antibody. P263-4

Maybe Count Dracula had malaria?
Female mosquitoes’ (the ones that bite for blood – the males are harmless) saliva has substances that facilitate her feeding, making the blood of her victims flow more readily (anticoagulant). But infection with plasmodium (the parasite that causes malaria) reduces the amount of these substances by ¾’s, making blood much more difficult to suck up… 22% of infected mosquitoes bite more than 1 person – thus helping to foster to the spread of the disease. This is versus only 10% of noninfected mosquitoes who bit more than 1 person. P275

Bats do not commonly carry rabies and when they do are unlikely to become aggressive and attack people; although handling a sick bat is still unwise. P276

Are we mice or men?
Toxoplasmosis is transmitted from its intermediate host (mice/rats) to its final host (cats) by predation. [How does the parasite foster this predation for its benefit?] Uninfected rats show a healthy aversion of cat scented areas, while parasitized rodents frolicked with abandon in them… This reckless behavior is clearly advantageous to the parasite… People are rarely preyed upon by cats but traces of infection are found in anywhere from 22% to 84% (France has one of the highest rates of infection!). Undercooked meat can be a major source (steak tartar bon appetit)… Infected men showed a greater propensity for disregarding rules while infected women were more outgoing, trusting and self assured… Infected people had slightly longer reaction times, a response that seems consistent with the effect on rodents; slower reaction times would presumably make a rat (or a person) easier prey… Those people with more recent signs of infection had a higher accident risk than people whose infection had been present for a long time... Even though humans are not the intended host of the parasite, it still influences the same brain regions that make the rats more vulnerable prey. P289

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