Intro to Parasites and Immunity

Lec 1-3

parasite

an organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host

Commensalism

a type of symbiotic relationship where one species obtains food or benefits while the other is neither helped nor harmed

Mutualism

two organisms of different species exist in a relationship in which each individual benefits from the activity of the other (ex: mitochondria, chloroplasts)

Parasitism

non mutual relationship between species, where the parasite benefits at the expense of the host

Prokaryote

unicellular, lacks membrane-bound organelles, 2 domains (Archaea and Bacteria), first living organisms

Eukaryote

has a cell nucleus, organelles enclosed within membranes, unicellular or multicellular

True or False: all “parasites” are eukaryotes so they are more similar to you than any other kind of infectious disease (other than fungal pathogens)

True

Mitochondria are thought to have evolved from ___ to generate the LECA (last eukaryotic common ancestor. Mitochondrial genomes encode ~_____ proteins

alpha-proteobacteria; 3-13

Chloroplasts are thought to have evolved from ___ after LECA acquired the mitochondrion. Chloroplast genomes encode ~____ proteins

cyanobacteria, 20-200

Prototrophy

the ability to synthesize all the compounds needed for growth (can grow in minimal conditions)

Auxotrophy

the inability of an organism to synthesize a compound required for its growth (this makes the parasite forever dependent on its host because parasite cannot synthesize)

Parasites are ancient

some are trapped in amber from 14-15 million years ago

Viruses

require host cell machinery to replicate (ex: rhinovirus/common cold, HIV/AIDS, influenza/flu)

Bacteria

prokaryotic, can be free living, some are obligate or obligate intracellular pathogens (ex: salmonella, staphylococcus, strep)

Fungi

eukaryotic pathogens, typically extracellular, cell wall can be targeted by drugs (ex: Candida/thrush, Athletes foot)

Protozoan Parasites

unicellular eukaryotes, some free-living, some must live inside host cells, some extracellular in a host

Helminth Parasites

multicellular “worms", some are free living in the environment, others only live in hosts, some must live inside host cells, while others are extracellular

Ectoparasites

parasites that live outside of its host (ex: lice, fleas, mites)

Malnutrition is exacerbated by _____.

increased population (not enough food), environmental degradation (decreased food yield), political conflict (disruption of societal structure)

Caloric energy is wasted by fevers caused by _____. Disease endemic human populations have waste of 22-30% of total energy yield from grain production.

human infections with parasites

Pathology

a deviation from normal health to disease

Pathogens

any extraneous organism (virus, bacteria, fungi, protozoan, or worm) that infects a host to cause disease

Primary vs opportunistic pathogens?

Primary pathogens cause disease in any healthy host while opportunistic pathogens are free-living or normal flora that are only pathogens in certain conditions.

Virulence

The degree of pathogenicity of a pathogen

Monoxenous

a direct parasite life cycle where all the stages are supported by a single host

Heteroxenous

parasite lives in more than one host during its life cycle

Definitive host

host where parasite becomes sexually mature (mating/offspring)

Intermediate host

host contains larval/asexual parasite stages

Vector

an organism typically, a biting insect or tick, that transmits a parasite from one animal to another (NOT same as reservoir host; harbors a distinct form of the parasite)

Reservoir host

non-human host that maintains the infection in nature (ex: dogs); harbors the same parasite stage as the human host; NOT same as insect vector

Obligate vs facultative vs opportunistic parasites

obligate requires a host for survival, facultative can survive outside the host, opportunistic takes advantage of circumstances to infect a niche or organism that it does not normally cause disease in)

Disease signs vs symptoms

Signs are changes in body that can be directly observed (fever, rash, swelling) and symptoms are changes experienced by patient (nausea, headache)

What are the different disease sources?

Human sources, animal sources (zoonoses: animal diseases that occasionally occur in humans), and inanimate disease sources (food, water, soil)

How are parasite transmitted?

Invasive, direct contact, foodborne, waterborne, inhaled, vector-borne

Vertical transmission

parasites can infect neonates during pregnancy (cross placenta), labor and delivery, and breastfeeding (passed through breast milk)

Contact Disease Transmission

Direct contact (direct touching like sexual contact), indirect contact (spread through inanimate objects like bedding), food and waterborne

Vector-borne Transmission (Mechanical vector vs biological vector?)

mechanical vector (external transmission): parasite is on surface of vector

biological vector (internal transmission): parasite replicates and changes within vector

Oral/fecal cycles

encysted protozoa or worm eggs persist in the environment after being shed in feces. These are ingested in contaminated food or water to initiate infection.

Hematophagous insects

blood sucking insects that are both hosts and vectors for protozoan and helminth parasites

What are some other routes of infection?

inhalation in fresh water, sexual transmission, some parasites directly invade into skin

Ecotone

a transitional zone between 2 adjacent ecological communities containing the characteristic species of each and exhibiting competition between the shared organisms

______ increase transmission because of human modification of the environment (deforestation, urbanization)

Overpopulation and urban crowding

What can cause fecal-oral contamination of environment?

lack of sewerage disposal systems, use of human feces as fertilizer (contaminates food and water)

What countries have urbanization that is unplanned, sprawling, and have thriving vector-borne diseases in the communities?

South and Central America, India, Middle East, and Africa

Dams slow water to create lentic environment. What is lentic?

still water; snails, black flies, and mosquitos thrive

The _____ in Egypt slowed the Nile river current and kids were infected by S. mansoni & S. haematobium after swimming in the Nile

Aswan High Dam

How does deforestation lead to more parasite disease?

• clear cutting of trees creates huge ecotonal zones (source of new infection, exposure to mammals with parasites)

• standing water after deforestation (opportunistic breeding site for mosquitos)

• changes soil types along banks of rivers (can change to soil ideal for parasites)

How does aquaculture and war affect parasite disease spread?

breeding sites for mosquitos means spread of malaria, war means less access to health care and safe food and water, more movement and crowding, stress significantly lowers ability to fight off agents

True or False: Access to affordable and effective medication is needed but the cost of bringing a new drug to the market is ~$2.5 billion.

True

Parasitic infections are mostly preventable with access to:

screens/bed nets/ insecticides (vector borne)

safe food/water/sewerage disposal (water and foodborne)

Parasitic infections are mostly curable with drugs that are:

affordable, effective (no resistance), and accessible

True or False: Parasites only infect one part of the body

False; parasites exploit diverse body sites

The parasite to do list:

1. Complete _____ (move host to host)

2. Enter host (____)

3. Migrate to appropriate _____ or ____ within host

4. Maintain position within host

5. Find a _____ (in host)

6. Successfully ____ in and release progeny from host

7. Undergo essential ____________ in host

8. Cope with physiological conditions in host

9. Evade destruction by host _______, at least until reproduction is complete

transmission, invasion, target tissue, site, mate, reproduce, developmental changes, immune system

Fecal-Oral Transmission To do:

Infectious form released in feces, contaminates food/water, inactive egg or cyst form withstands in environment, coincidental consumption by next host

Direct penetration transmission to do:

requires motile juvenile form with limited lifespan in the environment, can increase likelihood of host encounter by moving, can time emergence of invasive form with the behavior of the host to improve chance of encounter

Vector Transmission to do

moves from host to host using insect vector that feeds on blood from infected host, parasite must survive vector digestive tract, reproduce, and/or develop appropriately BEFORE transmission, adaptations increase likelihood of transmission

Vertical transmission to do:

infected mothers infect progeny (offspring), parasite migration across placenta during pregnancy, nursing infant consumes infectious breastmilk

What factors may result in unsuccessful transmission?

specificity (infection of certain cell types), habitats differ, metabolic & anatomic cues within host, interactions between host & parasite surface molecules, migration is not always successful, niches such as the blood and GI tract move

__________ makes it easier for parasite to find a mate.

Target tissue specificity

Some parasites are _____ (possessing both male & female reproductive structures).

hermaphroditic

In some cases, sex is not essential to replication but ____________________ by recombining genomes of co-infecting organisms.

increases genetic diversity

Parasite progeny must leave host: parasites exit from ________ while vector-borne parasites rely upon _____ for egress.

anus/in feces; insect

True or false: parasites change their developmental/gene expression in anticipation or response to new host

True

Many parasites use _____ to evade host immune response

variable surface antigens

Helminths express _____ that are used for migration through tissues and ____ that subvert the host immune response

proteases; genes

Developmental timing is responsive to what other cues?

host health, co-infection, parasite density, environmental conditions

Immune system

nonspecific and specific resistance; composed of cells, tissues, and organs; recognizes microbes and acts to neutralize or destroy them

Innate immunity

pre-programmed to respond to infections and cancer cells (first line of defense, recognizes general properties of infectious organisms, critical in the first hours to days of infection, less effective than targeted adaptive immunity, in place at all times)

Adaptive immunity

specifically responds to an individual infection (specific to new infectious agents, efficiently combats them, remembers how to combat in case of re-exposure, specialist for serious threats)

_____ and _____ imprisons pathogens.

Mucus and Antibody aggregation

_______ and ___________ assassinates pathogens.

Complement lysis and Cytotoxic T cells

__________ and __________ poisons pathogens.

Reactive oxygen intermediates and reactive nitrogen intermediates

Collateral damage

Damage to your body from immune defenses

True or false: parasites and other infectious agents continue to evolve mechanisms to evade immune system defenses in a biological arms race.

True

What are some of the organs of the immune system?

thymus (where T-cells mature), lymph nodes (produce and store cells that fight infection and disease), bone marrow (tissue in center of bone makes white blood cells that are destined to become lymphocytes), spleen (contains white blood cells that fight infection or disease, helps control amount of blood in body).

Circulating Immune Cells: Blood

transports nutrients and oxygen to tissues, eliminates waste and carbon dioxide, repairs wounds, and protects from infection

Plasma (fluid portion of blood)

has sugars for energy metabolism in tissues and clotting factors to stop blood loss, has antibodies and complement to fight infections (55% of fluid)

Cells in blood

platelets for clotting, RBC for transport of oxygen, WBC for immune defense

Blood carried through body in _____. Heart acts as the _____ and______ move blood.

vessels; pump; contractions

Arteries

carry blood away from heart to body tissues

Veins

carry blood back to the heart from the tissues

Capillaries

thin-walled vessels connect arteries to veins (exchange of oxygen, nutrients, wastes between blood and tissues; white blood cells pass through capillaries into tissues)

Lymphatic circulation: ____ portion of blood penetrates into tissues as “_______”.

plasma; interstitial fluid

Lymphatic vessels ___________ from tissues past lymph nodes (site of ______).

drain fluid; lymphocytes

Lymph is moved directionally _____ the heart.

towards

Lymph nodes contain _________ and can respond to ______ during infection.

immune system cells, foreign antigens

Innate immunity: examples of physical and chemical barriers?

lysozyme, skin, mucus

Innate immunity: examples of innate cellular defenses?

monocytes, macrophages, dendritic cells, and granulocytes

Physical barriers

innate structural properties that discourage microbe adhesion and growth

Chemical barriers

substances that are deleterious to microbes (chemical damage, sequestration of nutrients, etc)

Gastric juices

in the stomach, pH is 1-3, pepsin (digestive enzyme), mucus

Peroxidase

in saliva; produces superoxide “free” radicals that damage microbes by reacting with them

Lactoferrin

found in milk and mucosal secretions (tears and saliva); sequesters iron so microbes can’t use it

Mucus

mainly composed of mucins, a family of large, heavily glycosylated proteins which form gels & trap microbes

Skin: mechanical barrier to _______, organisms removed by _______, outermost layer of cells are ______, surface is _____ to microbes because pH is slightly ____, high _____ concentration, and dry

microbe invasion, skin shedding, dead, inhospitable, acidic, NaCl

Some parasites breach the skin if introduced by _______ insect vectors, actively _____, or exit from the skin.

blood-sucking, invasive

Mucus membranes line the cavities exposed to ______. It is attached to skin, but the surface is _____ unlike skin surface. It is bathed in mucus (contains antimicrobial substances) and resists _____ and ____ microbes.

external environment, living, penetration, traps

Types of parasites that breach mucus membranes

orally infection/oral-fecal, sexually transmitted, ocular infection

Respiratory system: turbulent ______ deposits microbes onto ______ surfaces. Mucous _____ microbes, they are transported away from the ____ and expelled by _____ or sneezing, and _____ washes microbes to the stomach.

air flow, mucosal, traps, lungs, coughing, salivation

Nematodes like _______ from lung bloodstream into alveoli, crawl into throat and are swallowed.

Ascarus cross