WHY WE GET SICK THE EVOLUTIONARY ECOLOGY OF DISEASE

Transcription

1 WHY WE GET SICK THE EVOLUTIONARY ECOLOGY OF DISEASE

2 A FACT Medical science rarely employs an evolutionary perspective

3 DEFINE DISEASE Abnormal or low performance

4 SOMETHING TO REMEMBER Symptoms and causes of diseases need not be synonymous

5 CAUSES OF DISEASE Non-infectious - selfgenerated or non-biological agent Infectious - biological agent that can be transmitted

6 4 QUESTIONS TO ASK Function of the symptoms (why?) Cause of the symptoms (how? Mechanism) Ontogeny of symptoms (time course) Lineage (of victim and if appropriate agent)

7 Ex. 1 - MORNING SICKNESS Most common during early pregnancy Nausea, vomiting, aversion to many foods especially rich foods Mechanism - hormonal shifts Lineage?

8 CLASSIC PERSPECTIVE Morning sickness is a side effect of hormonal change Is it?

9 FUNCTIONAL QUESTION Could morning sickness be adaptive? This sickness leads to elimination of various foodstuffs from the mother s diet and by association from the fetus nutrition

10 EXAMINE REJECTED FOODSTUFFS Margaret Profet classified food groups Commonality is that many are mutagens Mutagens cause greatest impact during early development - later stages of pregnancy are primarily growth related

11 MORE RECENT STUDIES In a Korean study, women with morning sickness ate less and ate less diverse diets Those women gained less weight and produced lighter, smaller babies A US study showed that women with m.sickness had same rates of malformation as those without

12 PREDICTION Women who suffer from morning sickness are less likely to bear children with abnormalities

13 Ex. 2 - ALLERGIES Symptoms - sneezing, coughing, weeping, inflammatory response How - Class E immunoglobulins (antibody) Response occurs after antibodies have bound to ingested or inhaled compounds Ontogeny - allergies can be gained or lost at any age

14 WHAT HAPPENS? Symptoms - sneezing, coughing, weeping all cause elimination of the foreign bodies Inflammation can isolate foreign bodies

15 A FACT Many allergins are carcinogenic

16 A PREDICTION Allergy sufferers should be less likely to be stricken with cancer

17 A PREDICTION Allergy sufferers should be less likely to be stricken with cancer A CONFOUND

18 A PREDICTION Allergy sufferers should be less likely to be stricken with cancer A CONFOUND People with high allergy rates may be found in areas with very high levels of carcinogens

19 THE HYGIENE HYPOTHESIS Medical - Early lack of exposure to infectious agents and parasitic worms (helminths) suppresses natural development of the immune system Darwinian immune system has evolved to expect mild suppression of the immune system good hygiene removes that suppression

20 TEST THE HYGIENE HYPOTHESIS Compare allergies (e.g. asthma) in developed vs. developing countries or in developed countries now vs. 100 years ago Confounds?

21 INFECTIOUS DISEASES A perspective: disease problems are first and foremost problems of population and evolutionary biology and and second a problem of symptoms

22 INFECTIOUS DISEASES EXPLANATION FOR SYMPTOMS: Host defense Manipulation by infectious organism Interaction between host and infectious organism

23 FEVER: GOOD OR BAD? Until last century, fever was considered as a positive event New, anti-fever drugs changed that view due to concerns of heat damage from extreme fever However, many viruses succumb to heat at moderate fever temperatures

24 FEVER: GOOD OR BAD? Raising body temperature in mammals leads to: Increasing resistance to: herpes simplex virus, poliovirus S. pneumoniae,gastroenteritis virus, and of ferrets to influenza virus. Preventing fever can lead to longer lasting symptoms of chicken pox and more viral export from common cold.

25 FEVER: GOOD OR BAD? Aside from damage of extreme fever, bacterial infections do not seem to suffer from exposure to high temperatures and might even prosper However, raising body temperature does not simulate all aspects of fever in mammals so reports of positive and negative effects of heat must be viewed with caution

26 FEVER: GOOD OR BAD? Fever reducing drugs may also: Reduce pain - host becomes more mobile Reduce inflammation - infectious agent moves through host

27 ANOTHER SYSTEM A FACT: (cold blooded) lizards and grasshoppers create a behavioral fever upon exposure to pathogens Lizards manipulate their temperature until it reaches that of fevered mammals Lizards and grasshoppers experience much higher recovery when fevered

28 BEHAVIOUR FEVER Feed Rest Bask

29 BEHAVIOUR FEVER IMPACT

30 PARASITE MANIPULATION Cholera Facts: Bacterial disease Acquired orally from untreated water or untreated foods Bacteria can live for up to 5 days on food Symptoms include severe diarrhea Vaccines are short lassting

31 INPACT OF CHOLERA Last major outbreak of cholera in Latin America caused illness in 400,000 people with 4000 deaths Outbreak in Peru caused economic losses of approximately 1 billion dollars in trade embargo

32 PARASITE MANIPULATION? Cholera bacterium releases toxin at a very high rate that causes host intestinal distress Humans respond by releasing large amounts of the bacteria via diarrhea Toxin doesn t harm human but dehydration does

33 A SOLUTION? Rehydration therapy reduces harm from dehydration but doesn t stop bacteria from spreading So, combine sugar water with rice starch