Commensalism: One of the two benefits and the other is unharmed or benefited. Neutral.

Mutualism: Coexistence where the host and microorganism are benefiting.

Parasitism: Parasites live at the expense of the host and the host will definitely be harmed.

Parasites don't usually cause acute infection; they tend to cause a chronic infection and maintain the health of the host because if the host dies, they need a new host, and that's just more work.

They try to maintain a relationship with the host where too much harm is done.

If the balance is thrown off, we will see the manifestation of the disease and it can be so severe tat the patient dies.

Toxoplasmosis, Cystosarcosis

*Protozoan parasites that can invade our body, go to organs, particularly brain and induce an inflammatory response that is not compatible with life

*ID an appropriate host

*Establish a productive infection by accessing approrpiate tissues and cell types

*Mechanism to establish an appropriate niche within the host

*Mechanism to minimize innate and acquired immune responses

*Establish a balance between reproduction rate to maintain host

*Viability and potential to spread to a new host

*1.4 billion are infested or infected all over the world; approx. 1/5 infested with ascorus limborcarus

*Resides in the GI tract

*When the egg is ingested, it goes into the stomach, hatches into larvae, and then invades into the intestinal blood vessels, in the blood it reaches the lung, the larvae grows there and then crawls up the alveoli, dips down into the esophagus, enters the intestine and resides there 

*If it is introduced to a pig body it will not survive, needs an appropriate host

*Once inside the host, they need to find the appropriate tissue

*They can go into the immune system and wait there forever unless they are consumed by a new host

**The pig has larvae in their muscle and when the pork meat is eaten by antoher host then they are infected by the tapeworm, and the infection is propagated

Single celled eukaryotes: Protozoa (NOT FUNGI)

Multicellular eukaryotes: Metazoa

*Includes Helminths (worms), Arthropods (insects, arachnids, crustacea, mites), Mulloscs (snails)

**NOTE: Many arthropods and some molluscs do not directly cause disease but act as VECTORS or RESERVOIRS for both protozan and helminth parasites

Several bacteria and viruses are transmitted by arthropod vectors.

Protozoa: Entameba coli

(MUST KNOW THE TWO FORMS FOR THE EXAM; THEY ARE THE TWO UNIQUE FORMS OF PROTOZOAN PARASITES)

Gastrointestinal amoeba

Two forms: Cyst and trophozoite

Don't really need to know it but...

*Cyst has a chromatid body and 4 nuclei with a central karyosome

*Trophozoite has a single eccentric nucleus, a course cytoplasm and peripheral chromatin

Classification of Protozoa

(VERY IMPORTANT)

Protozoa are classified by organs of locomotion and reproduction

*All reproduce by binary fission, except for soporzoa which reproduce by schizogony/sporogony (meaning multiple fission)

*Locomotion

**Rhizopods - Pseudopods (amoeba)

Cilliates - Cilia

Flagellates - Flagella (long flagella)

Sporozoa - No locomotion

Plasmodium species: Causes malaria and toxoplasma

No locomotion

Reproduce by schizogony/sporogony

Causes granulamotous lesion in the brain

*Locomotion - psuedopods

*Reproduction - binary fission

Parasitic Protozoa - Flagellates

(Ex: Giardia, T. vaginalis)

Locomotion - Flagella

Reproduction - Binary Fission

*Giardia - Number one cause of water borne infection in the US - GI Infection

Pear shaped organism, multiple flagella and ventral structures

*T. Vaginalis - STD, Has flagella with corkscrew motility

Parasitic protoza - Ciliates

(Ex: B. Coli)

Locomotion - Cilia

Reproduction - Binary Fission

*Hair like golden cilia

They will have one or two flagella arising from a depression on the side of the body

Have a single mitochondria that will run length wise

Ex: Trypanosoma and Leischmania

*Leischmania - Can cause visceral or skin infection

*Trypanosoma - Two types

**Brucei - Latin American, Chagas disease, Causes cardiac myopathy (close to 100,000 patients but most are immigrants)

**Cruzi (African, Sleeping disease, affects the brain)

Flagellates - Divide longitudinally; longitudinal binary fission

Ciliates - Divide horizontally; transverse binary fission

Amoeba - Split via binary fission

Sporozoa - Divide by sporogony or schizogony; multiple fission

*Ex: Plasmodium (malaria), infects RBC, undergoes multiple fission

Sexual reproduction of protozoan parasites

Ex: Cryptosporidium parvum

*Largest water borne epidemic in the US

Ex: Person excretes protozoa into water and people consume it

*They acquire the cyst of CP which goes into the stomach to the intestine where it undergoes both asexual and sexual reproduction

*Asexual cycle goes on (merozyte Type 1); undergoes fission

*Sexual cyle: Merozyte 2 differentiates into a micro or macro gamete and they come together to form a zygote

**They form a thick wall cyst (secreted) or a thin wall cyst (which reinocculates the wall and continues its cycle)

Metazoa - Multicellular

Characterized on the basis of their reproductive system, their body configuration, alimentary tract, and how many intermediate hosts they require

3 types: Roundworm (Nematode), Tapeworm (Cestode), Fluke (Trematode)

Body is spindle shaped

Separate sexes

Have a tubular alimentary tract

Intermediate hose count is variable

*Multiple hosts for tissue nematodes

Exception: Intestinal tract nematodes don't need any intermediate hosts

*It is in our GI tract, ovum will be released in stool, another human will acquire the disease from underprepared food

Head with segmented body

Hermaphrodites (bisexual)

*Exception: Schistosoma group has separate sexes

Segmented so no alimentary tract

*Each segment can survive on its own

Has only one host (Ex: Tinea solica)

*Exception: Diphyllobothrium group has two hosts

Leaf shaped

Hermaphrodite

Blind alimentary tract; they eat and secrete through the same orifice (only one)

Has two hosts

*Exception: Chistosoma group has one host

Parasitic Helminths - Nematodes

*Examples

Pin Worm

Roundworm

Woucherarria Spp.

Loa Loa - Eye worm; exits from teh eye of the host

Parasitic Helminths - Cestodes

*Examples

Pork tapeworm

Tapeworm "segments"

Scolex

E. Granulosus - causes hydrative cysts

***ON HIS SLIDE HE HAS E. GRANULOSUS UNDER TREMATODES, ON MEDIASITE HE EXPLAINED THAT IT WAS INCORRECT***

Parasitic Helminths - Trematodes

*Examples

Schistosoma

Liver fluke

Arthropod Parasites as Vectors

*Mosquito - Malaria and Filaria

*Tsetse Fly - African trypanosomiasis (African sleeping sickness)

*Riduvid bug - Chagas Disease (American)

*Sand fly - Leishmaniasis

*Crysops fly - Loa loa eye worm

*Tick - Babesiosis; Lyme disease

A host is an organism in which the parasite spends its life

A parasite may need just one host, or may need more than one to complete their life cycle

Two types: Definitive and Intermediate

Example: Protozoa Malaria is transmitted by the mosquito

*The host in which the protozoa spends its sexual stage of life with

*Ex: Trichomonas vaginalis

Example: Helminths

*The host in which the parasite (metazoa) spends its adult stage of life cycle with

*Ex: Tinea soleum; tapeworm

*Larvae consumed in meat, hatch in stomach, go into intestine and stay their entire life

Example: Protozoa malaria in humans

*The host in which it spends its asexual life cycle in

*Ex: Plasmodium

Example: Helminths

*The host in which the helminth spends its larval stage of life cycle with

*Like inside a pig

1. They need an appropriate environment for life cycle stages

2. Transmission to a definitive host (allows for sexual recombination and diversity) OR intermediate host (allows for higher levels of parasite in the population)

3. Mechanism to survive in the environment in the absence of an appropriate host

4. Maintain a dormant state within a host to permit transmission under the right conditions

Sometimes they can be found in meat and carnivores will consume them

OR

They can be excreted in feces and lay dormant in the environment for a long peroid of time in a cyst formuntil they find a host (ex: toxoplasma)

*Toxoplasma is harbored in feline GI tracts; when cleaning the litter box you have a chance of exposure, avoid while pregnant

Toxplasma can cross the placental barrier and is life threatening to the fetus.

Toxoplasma Question (Advice from 2nd years students)

What is the most common cause of infection by toxoplasma?

Answer: UNDERCOOKED MEAT

He might give you a clinical vinette about a person who works at a pet store and cleans kitty litters and is always around feline feces and then say, "what is the most common cause of infection by toxoplasma". The answer (according to second year students) is ALWAYS undercooked meat.

Carniverous Behavior - Ex: Pig tapeworm

Close contact with animals (Vets, meat packers, animal handlers)

Contact with Infected Waste (feces, urine) - Ex: Hookworm

Arthropod and other invertebrate hosts

Direct transmission from one vertebrate to another

Direct human to human (sex, handling infected tissue, transfusion)

Can be transmitted through walking barefoot on soil contaiminated with feces and urine.

The hookworm have larvae found in the soil and when someone walks barefoot the larvae will invade through the skin and enter the circulation to the intestine.

Hookworm have hooklets that latch on to GI mucosa, causing persistent bleeding which leads to iron deficient anemia

1. They find themselves in diverse enviornments to which they need to adapt

2. Life cycle stages reflect adaptions to these environments

Ex: Toxoplasma in feline feces

3. Establishment an dpropogation in the vertebrate vs. invertebrate host

4. Acute vs. Chronic infection

*Ex: Chronic infection for their own benefit

5. Form of dissemination

6. Survival outside the host

Ex: Larva in pork, handling of kitty litter, food with cistode or nematode eggs

Life cycle of a parasitic helminth

(Taenia solium, the pork tapeworm)

Part I - The intermediate host

Pig ingests contaminated food containing ova or proglottid

*Proglottid - Tapeworms; hermaphrodites with segments of both male and female reproductive organs

Pig consumes the ova, which hatches to larva, circulates in blood and is eventually trapped and insisted into muscles

Life cycle of a parasitic helminth

(Taenia solium, the pork tapeworm)

Part II - The definitive host

With carniverous behavior, humans consume undercooked and infected meat

The cysts will hatch, larva are produced and the larva pass to the intestines, grow into adulthood and reside in the GI tract.

When the adult inhabits the human GI system, they shed some of the proglottids and ova (proglottids are filled with ova)

***Humans can accidentally become an intermediate host and harbor the larval eggs. Larva in circulation will disseminate to different organs of the body including the brain.

Known as cysticercosus - humans are intermediate host

General form of life cycle for parasitic helminths

Eggs --> Larva --> Mature Worm --> Mating --> Eggs...

These stages can occur within the same host or involve multiple hosts/environmental conditions

Remember, they want to create a chronic and long term infection.

*They need to avoid or modulate or subvert the immune system to ensure long term residence

(ex: can be metabolically inactive - cyst form)

*May reside in a viable but metabolically inactive form

*Manipulation of the immune response should not be global, as in infection with the "acute" pathogens, which may kill the host

*Parasite load should not exceed the capacity of the host to support the maintenance of its nutrient supply

*Ideal parasite does not infect the "fitness" of the host

*Ensure transmission to a new host

Every component of the immune system will come into action (innate and active) to eliminate the pathogens

*Innate (nonspecific) - Intact skin/gastric acid/peristalsis/mechanical clearance

*Active - Complement/antibody/cell mediated

*Acquired immunity to control subsequent infection

*Sequestration of the pathogen; granuloma formation

*Sequestration of nutrient source

If the parasite does not cause harm, the body will not attack them (No harm no foul principle)

*Parasite does not want to produce significant loss of "fitness"

Stages of Parasite Infections

(KNOW THESE)

Incubation period: Time between acquisition of infection and appearance of symptoms (hours - years)

Prepatent period: Time between acquisition and demonstration of pathogen (from blood or feces)

*Can be shorter than the incubation period (days - years)

Patent period: Time frame when an organism can be demonstrated in the body of an individual. Doesn't need symptoms. (days - years)

Enterobius vermicularis: Pinworm

50 million

1 in 5 has pinworm; exists in adults asymptomatically

1.4 billion

1 in 5 worldwide

300,000,000

Many millions die every year

Many acquire the disease every year

In the US, we don't spread malaria because we don't have the vector

Diarrhoeal Diseases - 3.1 million

Malaria - 2.1 million

Roundworm and Hookworm - 165,000

1. Poor sanitation

2. Failure of sanitation measures (water treatment facilities)

*Due to many reasons: civil war, lack of resources

3. Contact with symptomatic and asymptomatic carriers

4. Animal to human transmission

*Toxoplasma, tinea solium (pig tapeworm)

5. Presence of an appropriate vector

6. Long incubatoin/latency period of certain parasitic infections.

1. Global travel (particularly by air, "Airport malaria)

2. Immunosupression due to HIV/AIDs, chemotherapy, organ transplant

3. Institutionalized populatoins (linked to poor sanitation/hygiene)

4. Migration/immigation

Ex: Chagas disease leading to cardiomyopathy (common in latino immigrants)

5. War/Civil Unrest leading to breakdown of public health/sanitation systems

6. Famine (malnutrition and weakened immunity)

7. Behavioral aspects

Ex: Anal sex spreads giardiasis

1. Eosinophilia - A salient feature of helminth infection found in a CBC

*Once seen indicates parasites or allergies

2. A detailed history - travel, food intake, socioeconomics

3. Cornerstone of diagnosis is identification of the parasite

Stool - ova of worms and cysts of protozoa (seen in wet mount or stained smear)

Urine - schistomahematobium; causes bladder cancer and is typical from someone swimming in the nile river

Sputum - lung flukes

Blood - pasmodium, leishmania

Tissue - A skin/muscle biopsy may be necessary

*Larva in pig muscle can be found via biopsy (ex: Trichinella species)

Serology Tests

*Detection of antibodies - Used for toxoplasmosis

*Detection of antibodies - In blood (Plasmodium), body fluids (P. carinii and T. vaginalis), tissues (T. Condii) and excreta (E. histolytica, giardia and cryptosporodium)

Molecular Biology Techniques

*DNA probes for P. falciparium, T. Cruzi, T. Brucei, Onocoerca Spp. and agents of lylmpahtic filariasis 

Inerfere with nucleic acid synthesis (majority of drugs)

OR

with carbohydrate metabolism (less common)

Host and parasite may have comparable target site for chemotherapeutics.

Differential toxicity is achieved by

1. Preferential uptake

2. Metabolic alteration of the drug by the parasite

3. Differential susceptibility of the comparable sites in parasite and host

Not achievable (can't get all of these), but...

1. Effective in a single dose

2. Easily administered

3. Safe enough to be dispensed with limited medical supervision

4. Is relatively inexpensive to be widely used

*Chronic infections - require long term teratment without an achievable "sterile cure"

*Lack of antiparasitics because poor countries suffer from it; not profitable for pharmaceutical companies

*Domesticated animals have drugs (veterinary parastic focus), but poor people where the infection is common do not have those resources

*No vaccines because parasites will spend their life in different organisms

*If some are asymptomic, how will you know someone has an infection? Reservoirs