Lecture 23 - Defense Mechanisms Against Disease

Species Barrier (Species Immunity)
Many diseases cannot transfer from species to species. For example, smallpox and Salmonella typhi are only hosted by humans

However, there are about 250 diseases that can pass between humans and lower animals, for example, salmonella food poisoning can pass from dogs to humans.

-Tuberculosis
There is a high incidence of Tuberculosis in American Indians, but that can be linked to poor nutrition.

-Malaria
Malaria has caused 10-15 mutations in black Africans that help them wistand malaria. These mutations include sickle cell anemia and the duffy factor. An absence of a duffy receptor prevents malaria parasites from entrering the cell.

-**CCR5 gene (AIDS)
5% of the all Americans have the delta 32 mutation, which helps them survive the AIDS virus by producing a misshaped CCR5 co-receptor on the white blood cell, a receptor that facilitates the infection of the AIDS virus. 14% of white Americans, 2% of central asians, and no other race has a high number of this mutation. The mutation might have become more prevalent during either the black plague or during the smallpox outbreak.

Individual Immunity
You may be predisposed to a certain disease, even more than your direct relatives. Athlete's foot, multiple sclerosis, human herpes 6 and 4, and rheumatic fever (Strep pyogenes).

Age
Very young and very old people are more susceptible to disease due to their weak or weakened immune system. Babies have low levels of serum protein like albumin, which would work as complements. Complements can attach to an antigen to help antibodies recognize the foreign matter.

Gender
Gonorrhea and syphilis can be more benign in females, who will act as healthy carriers. UTIs are also more prevalent in females because they have a shorter urethra.

Mental State
Mental state can affect severity of certain symptoms thanks to hormones such as endorphins.

Living Conditions
Middle or upper-class are more educated and have better hygiene. This leads to less exposure to pathogens. However, this means that the body's immune system is not trained and can lead to more diseases later in life. The lower class is usually more exposed to diseases, which strengthens their immune system.

Occupation
Miners can get asbestos particles in lungs which can lead to infections and cancer in mines. Firefighters get commonly exposed to the Hepatitis C virus, which has a long incubation period of 20-30 years.

Fatigue
People are more prone to infectious mononuclelosis and herpes simplex 1&2 when tired/fatigued.

Poor Nutrition**
Poor nutrition is the #1 reason for individuals being more prone to infections.

Skin
When intact, skin has interlocking layers that protect against some organisms. However, S. aureus, dermatophytes, Neisseria gonorrhea, and Chlamydia trachomatis can all grow on/through skin. Skin (stratum corneum) sheds and can contaminate many things. Also referred to as an "acid mantle", the skin has a pH of 4.5 to 6.5. Resident flora live on your skin and produce antibacterial fatty acids, which destroy most transients (passing organisms).

Mucous Membranes
Mucous membranes in the nasopharynx trap large particles and prevents them from entering the respiratory tract, and transports them into the GI tract to be dissolved. Mucous membranes fail to protect people from microaerosols, which can contain TB.

-Stomach
The stomach is thick-walled and acidic. There is a thick mucous membrane that protects the stomach from acid and also most infections. It has an extremely high pH of 1-3.

-Small Intestine
The duodenum pumps out bile, which kills gram-positive bacteria.

-Large Intestine
The large intestine, or colon, is favorable for bacterial growth. It is thin-walled and lined with some mucous. Pooping clears the large intestine.

Eyes
Tears mechanically flush the eyes, and also contain Immunoglobulin A (IgA), an antibody protects against recurring infections, and lysozymes.

Genitourinary tract
Contains mucous offers some protection (not much so use a condom).