One member, the parasite, lives in or on another oragnism, the hosts, at the expense of that organism

The host may or may not be killed

"living together"

Any plant, animal, protist or helminth that is intimately associated with another organism of a different species; each member is termed a symbiont

A fetus is not a parasite or symbiont b/c they are the same species

Phoresis

Commensalism

Mutualism

Predation

Parasitism

-means traveling together

A smaller organism, termed the phoront, is carried mechanically by the host.

ex/ bacteria, fungus, mites or leech carried on your skin

-when one symbiont, the commensal, benefits and the other animal is neither helped nor harmed

True commensalism difficult to find, and my not even actually exist. Close inspections usually reveal either a mutualistic or parasitic association

Each member, a mutualist, depends upon the other; obligatory  or facultative.

Ex/ flagellates produce cellulase in gut of termites

one member, the predator, benefits and a smaller organism, the prey, is harmed; usually eaten

The preditor/prey relationship is not usually considered a type of symiosis, but it technically falls under the definition

the study of the relationship between a parasite and its host

Parasitic relationships may be temporary, facultative or obligatory

Ectoparasite: live on the surgface of the host. Animals are infested not infected. EX/ ticks, lice, fleas

Endoparasite: live within the host. Animals are infected.

Ex/ roundworms and tapeworms in gut

Hyperparasite: parasite within a parasite

-Transmits parasites from host to host

Biological Vector: are organisms which transmit parasites (mosquitoes infected with malaria)

Mechanical Vector: nonliving transmitters of parasite stages (bed clothing containing lice or spoon containing pinworm)

- same thing as vehicle

involved with some development but the parasite does not reach sexual maturity; often asexual stages or larval stages

EX/ Plasmodium falciparum which causes Malaria undergoes its sexual stages inteh mosquito, making humas the intermediate host.

Non-human animals that serve as sources of infection to humans

Ex/ man acquires the infection from eating raw fish containing parasites.

1. Multiple fission: in protozoa (Eimeria oocyst)

2. Hermaphrodism: of trematodes

3. Parthenogenesis: in Strongylodies spp.

4. Strobilation: of tapeworms high ova output

5. High ova/larval output: of many worms

1. loss of digestive tract of tapeworms

2. loss of wings of fleas and lice

3. loss of many sensory structures of nematodes

4. development of tegument

5. development of special holdfast organs, ex/ hooks

6. production of anti-coagulants in leeches

1. Oftenspecial site specificity

2. Usually, but not always, non-lethal to host

3. Generally more numerous than hosts

4. Generally much smaller than host

(if larger, then termed a predator)

5. Often have evolved methods of evading host immune system

1. Antigenic variation (Trypanosoma)

2. Tough tegument (acanthocephalans)

3. Intracellular habitat (coccidia)

4. Antigen acquisition/mimicry (shistosomes)

5. Suppression eosinophil or neutrophil migration to the site of the parasite (Onchocerca sp.)

6. Encystment (Trematode metacercarial cysts)

7. Ability to cleave antibodies or consume complement

8. Trigger immune response

Pathology Due to Parasite Infection is Variable:

Physical Trauma

1. migration of nematodes through tissues

2. ulceration of intestinal wall and liver by cysteine proteases of Entamoeba histolytica

3. displacement of tissue or structures by hydatids

4. protease digestion of epithelial cells by Trichomonas vaginalis

5. ulceration due to insertion of hooks, spines into intestinal wall

Pathology Due to Parasite Infection is Variable:

Nutritional Diversion

1. giardiasis results in diarrhea

2. malabsorption (Diphyllobothrium absorbts vit B12)

Pathoogy Due to Parasite Infection is Variable:

Toxins/Excretory products/ Immune complexes

1. African trypanosomes slough antigen/Ab complexes that are absorbed by RBC's; complement is activated

2. Massive RBC lysis (excretory products of some trematodes and cestodes causing anaphylaxis)

3. Fibrosis and inflammation around schistosome eggs (granulomas, fibrosis, edema against adult filarids)

4. Blood loss (hookworms and anaemia)

1. Ingestion (from food, water or inhalation)

2. Vectors

3. Direct Penetration (of skin from environment)

1. Treatment

2. Understanding epidemiology

3. Implementation of control measures

4. Fundamental research

1. Fecal Specimen Collection (Direct, wet, concentration, floatation, stained slide)

2. Colleciton of Material other than fecal (Perianal specimens, Sigmoidoscopic material, Duodenal aspirates, Liver abscess aspirates, sputum, urine urogenital)

3. Blood films/smears

1. Some parasites morphologically indistinguishable

2. Parasites hidden in host tissue

3. Low sensitivity

Problem: current parasitological diagnostic techniques not satisfactory

Solution: Need trained staff, equipment

1. Biochemical (first generation)

- Enzyme patterns

2. Immunological (antibodies)

3. Nucleic acid (DNA)

Enzyme Patterns:

Isoenzymes

Perform same function BUT different movements on gels

- enzymes separated by size

Genetically controlled: parasites with different gel patterns genetically distinct

Used for analysis of Chagas' disease

Antibody based diagnosis

Advantages

1. Rapid easy field-based test

2. Both individual & mass population screening

3. Ig subclasses- to improve specificity & sensitivity

Antibody Based Diagnosis

Disadvantages

1. Cannot distinguish past/ present infections

2. Cannot distinguish morphologically similar parasites

3. Expensive to develop- significant research prior to commercialization

Example of Antibody Based Molecular Diagnosis

African Sleeping Sickness

Anti-trypanonosomal IgM detected by simple/rapid CATT

(Card Agglutinatino Test for Trypanosomiasis)

Drop of blood -->

Mixed with fixed parasites on plastic card --->

Blue granular deposits = infection --->

25 US cents per test

Kits for Chagas' & malaria

Westerns for cestodes

DNA probes

Polymerase Chain Reaction (PCR)

Amplifies target sequence and increases sensitivity

1. Ribosomal DNA/RNA

highly sensitive, No good for closely related species

2. Specific sequences of genomic DNA

Highly specific for single species- not sensitive

3. Random primer amplification (RADP) PCR

Very highly sensitive - Not specific

Nucleic Acid Based Molecular Diagnosis

Advantages

1. Genomic DNA constant - parasite & hosts unique DNA sequences

2. Very sensitive- small biopsy

3. Probes can be designed with flexibility

Specific - detect single parasite species

Less Specific - detect group of parasites

Nucleic Acid Based Diagnosis

Disadvantages

1. Expensive - especially PCR

2. Radioactivity needed: newer non-radioactive probes

3. PCR can fail - Contamination & false positives

4. DNA probes do not distinguish between dead and living parasites

Chagas' Disease - PCR based kit in trials in Brazil. Aims to replace Xeno-test