Immune System Summary There are three lines of defense a pathogen must defeat in order to create a problem/illness/disease in our bodies. 1) Skin and Mucous Membranes 2) Non-specific Immune Responses (Macrophages, Neutrophils, fever, inflammation) 3) Specific Immune Responses (B cells, T Cells, Antibodies)

Immune System Summary To get by the first line of defense, skin and mucous membranes, the pathogen must either find a break in the skin (i.e. cut) or use a pre-existing entryway. Most common entry points after a cut or scrape are through the respiratory system (nose and mouth), through the gastro- intestinal lining (we eat it) and lastly through the genitourinary tracts.

Immune System Summary To beat the other lines of defense, the pathogen uses biochemical trickery. It either blocks the immune cells from recognizing it as foreign or it terminates them.

Pathogens want inside us All human pathogens want to get inside our body in order to multiply. The human body’s core temperature is in the optimal range for the reproduction of most pathogens.

#1) Insect-Borne Vectors Insects form a large portion of pathogen vectors because many of them are hematophagic, meaning they feed on blood at some point in their lifecycle. Mosquitoes, ticks, lice, fleas and some flies are examples of insect vectors. Other animals can be vectors as well, but not as common as insects (i.e. rats, mice, cows, deer…).

#1) Insect-Borne Vectors The pathogen is picked up by the vector insect at some other point and transferred to the human host in many ways, each circumvents the first line of defense, the skin.

#1) Insect-Borne Vectors Some insect vectors pierce the skin with a specialized mouthpart (i.e. mosquito). Others simply bite the skin and create a pool of blood (i.e. black fly) The triatomine bugs, responsible for passing on the protist which causes Chagras’ disease, defecates the pathogen out while it feeds and the host rubs it into the wound in response to the bite! All these methods pass the pathogen right into the bloodstream where it can do the most damage.

#2) Droplet Contact Many pathogens require the air to provide a pathway to infect other hosts. The pathogen particles travel from one host to another through the air in a cough or a sneeze. The pathogens get in the body through the respiratory tract.

#3) Direct Contact Pretty straightforward… An infected person with outward signs of infection makes physical contact with an unaffected individual and passes on the pathogen. In many cases the contact is sexual.

#4) Indirect Contact An infected individual touches a surface and leaves the pathogen on that surface. An unaffected individual touches the same surface later on and picks up the pathogen. Pathogen only gets in if that body part contacting the contaminated surface is then placed around an entry into the body (i.e. hand in mouth). Some, like ringworm, don’t need entry.

#5) Fecal-Oral An affected person does not wash their hands after going to the bathroom and transfers a pathogen to a food source. Can also happen if raw sewage mixes with drinking water. These ways enter through the mouth and then the gastrointestinal tract.

#6) Vertical Transmission This is when an affected mother passes the pathogen on to her developing fetus through her bloodstream. Usually sexually transmitted diseases (STDs) like HIV, Hepatitis B, Syphilis, etc…

#7) Airborne (aerosol) Transmission Not a natural way for a pathogen to be released. This is where a pathogen is released in tiny droplets of water that hang in the air for long periods of time. Considered bioterrorism. The USA has “BioWatch” to analyze air samples and ensure terrorists have not released pathogens into the air over a major city center.

Homework 1) What the three lines of defense a pathogen must break through in order to cause illness in a human. 2) Indicate 5 places on the human body that a pathogen may try to enter. 3) For each type of transmission, indicate two pathogens (as specific as possible) that follow that method of infection. 4) Other than vertical transmission, indicate one way you could protect yourself against each type of transmission.