Lecture 2: Life Cycles Flashcards
definitive, intermediate and paratenic hosts apply to: endoparasites or ectoparasites?
endoparasites
definitive host
primary, principal final host
host in which the adult, or sexually reproductive, stages of parasite occur
intermediate host
host required for parasite development but in which parasite doesn’t become sexually mature
paratenic/transport host
parasite does not undergo any required development but it remains alive and infective to another host (could be the definitive host or a different species that serves as paratenic host)
what happens when definitive host ingests the paratenic host
parasite completes its development
do direct life cycles include intermediate hosts
no
does direct life cycle include definitive host
yes
Monoxenous parasites
Parasites with direct life cycles
Direct life cycle Infective stage: Resting vs active stage
Resting = mode of transmission is ingestion
Active = ingestion, penetration of skin, sexual contact
Direct life cycle: definition
Life cycle that includes a definitive host but no intermediate host
Indirect life cycle: definition
Requires an intermediate host
Heteroxenous parasites
Indirect life cycle with intermediate host
Examples of monoxenous parasites (2)
Nematodes and Protozoa
Examples of heteroxenous parasites (4)
Trematodes
Most tapeworms
Nematodes
Protozoa
Indirect life cycle infective stage: resting vs active stage transmission mode
Resting = ingestion
Active = penetration of skin, vector
Examples of spirurid nematodes found in pigs’ stomachs (2)
Ascarops strongylina
Physocephalus sexalatus
Where can you find/identify ascaris sum eggs
Swine feces
Pathogenic changes: ascarids
Larvae migrate through liver and lungs
Damage to lungs
Secondary bacterial infection risk
How to treat ascaris (swine)
Deworm confined sows 1 week before farrowing
If moved out of confinement, deworm every day for first 30 days then in 8 week intervals
Environmental control: ascaris
Eggs very resistant to environmental degradation and disinfectants
Can destroy eggs by intensive steam cleaning, flaming, prolonged exposure to full sunlight
Ascaris cross species infections
A. Suum (pigs) and A. Lumbricoides (humans)
People who work with pigs get swine ascarids and vice versa
Direct life cycle + paratenic host: definition
Paratenic NOT required for completion of parasite’s life cycle
But it does facilitate transmission to definitive host
Stephanurus dentatus is an example of parasite with what kind of life cycle
Direct with paratenic host
Stephanurus dentatus: 4 modes of transmission
Ingestion of free infective larvae
Ingestion of earthworm/paratenic host carrying infective larvae
Penetration of skin of pig by infective larvae
Transplacental transmission of pig by infective larvae
Most infections with Stephanurus dentatus occur by which transmission method
Ingestion of free infective larvae
Stephanurus dentatus: how paratenic host contributes to life cycle
Earthworm not required for host to complete life cycle
Earthworm ingest Stephanurus larvae and don’t develop further but are instead waiting for pig to eat earthworm
Stephanurus dentatus is what kind of parasite (hint: general classification and life cycle)
Monoxenous nematode
Example of paratenic host with heteroxenous parasite
Spirometra mansonoides tapeworm
Arthropod ectoparasites serve as (2)
Parasites
Vectors
2 main life cycles of arthropod ectoparasites (2 general names)
Holometabolous/complete metamorphosis
Hemimetabolous/incomplete metamorphosis
Holometabolous metamorphosis: process, does morphology differ between larval and adult stages?, what stage molts during growth
Egg —> larvae —> pupa —> adult
Morphology of larval stage very different from adult
Larval stage molts several times during growth
Variation in what stage is parasitic
Hemimetabolous metamorphosis: 2 possible processes with examples of general ectoparasites
Egg —> larva —> nymph —> adults (ticks, mites)
Egg —> nymph —> adult (lice)
Hemimetabolous metamorphosis: does morphology of larval stage differ from adult?, what stage molts during growth, variations that exist
Larval/nymphal morphology similar to adult
Nymphal stages molt during growth
Eggs can be laid on host or in environment, all active stages can be found on 1 host or different stages can be found on different hosts
6 modes of transmission for parasites
Ingestion
Penetration of skin/mucous membranes
Vector
Direct contact/sexual
Transplacental
Transmammary
Possible infective stages (7)
Egg
Larval worm
Protozoan cyst
Protozoan trophozoite
Arthropod larvae
Nymph
Adult
The stage exiting the host is called
Diagnostic stage
Predilection site definition
Preferred site of adult or sexually/asexually reproducing stage within or on host which is characteristic for particular parasite species
Dirofilaria immintis: generic name
Canine heart worm
Dirofilaria immitus: mode of transmission, infective stage, predilection site of adult, route to predilection site, mode of exit, exiting/diagnostic stage
Vectored by mosquitos
L3 —> deposited on skin then migrates through mosquito bite wound and into dog
Pulmonary arteries, right ventricle
Venous circulation from abdominal/thoracic muscles
Blood ingested by mosquito
Microfilaria in blood
Ascaris suum: locations and timing/duration of different stages, when are first eggs passed in feces, how long do adults live
Infective eggs ingested —> larvae hatch and migrate from small intestine —> liver (within 8-18 hrs of infection) —> lungs (4-6 days after infection) —> bronchial tree —> trachea —> pharynx —> small intestine (8-10 days after infection) —-> mature and mate in SI
First eggs passed 6-8 weeks after infection
Adults live 6-9 months
Ascaris suum: pathology
Larval migration through liver = hemorrhage, fibrosis, lymphocyte infiltration —> white spots(milk spots)
Larval migration through lungs = hemorrhagic lesion, eosinophil infiltration, severe/repeated infections cause edema/pneumonia/emphysema/death
Maturing and adult worms in small intestine = inflammation, diarrhea, rob host of nutrients, obstruction possible
Prepatent period definition
Time between infection of definitive host and appearance of stage exiting host
Ascaris suum: diagnosis
**prepatent period
Clinical signs = chronic paroxysmal cough, abdominal breathing, weight loss
Postmortem = liver/lung lesion, larval worms in lung tissue, large immature worms in SI
Patent infection = eggs/adults in feces
Main pathologic events occur during which stage of infection
Prepatent
Ascaris suum: treatment (3)
Pyrantel and fenbendazole = kill migrating larvae
During respiratory phase of infection
Supportive care + tx for secondary infections
How long is prepatent period for ascaris suum
6-8 weeks
How to control prepatent period of ascaris suum
Deworming!!
Locations of different stages external to host (6)
Soil
Water
Vegetation
Fomites
Intermediate host
Paratenic host
Ascaricosis of swine: epidemiology
Infective eggs are sticky/resistant/long lived and found in contained water, soil, water, vegetation, walls, floors, fomites
Infective eggs transported by pigs, people, other mammals, insects, worms
What information is needed for parasite control (environment)
Distribution and numbers of infective stages
Environmental assessment: ascaris suum eggs
Soil/vegetation samples from pastures
Soil samples from dry lots
Analyzed for eggs
Control of ascaris suum (what is the name of this technique)
Cleanliness, deworm and wash sows before farrowing
“Dose and move” —> deworm before moving to clean areas, use pasture rotation
Environmental conditions that promote development/survival of stages external to host (3)
Temperature
Humidity
Shade/exposure to UV light
Development/survival of what 4 external stages are affected by environmental conditions
Eggs = helminths, ectoparasites
Helminth larvae
Larvae/nymphs of ectoparasites
Protozoan cysts
Transmission hiatus
When environmental conditions are enough to inhibit growth/survival of parasites so anthelmintic tx not necessary
Ascaris suum eggs: winter vs spring (and why this is important for prevention)
Winter = eggs accumulate but don’t develop
Spring = eggs develop and become infective
Move pigs to safe pasture before spring rise in temp
Environmental conditions that promote and deter ascaris suum egg infection
25 degrees C, moist, shade = become infective in 2-4 weeks
Below 15 degrees C= will not develop
Low humidity/heat/direct sunlight = reduce survival
Resist freezing
Remain viable for 10 years
Ascaris suum: control strategies to reduce infection rates (2)
Daily removal of feces from and thorough cleaning of indoor facilities, outdoors feeders/waterers
Weaning and removing pigs from infected sows before the eggs that are shed from sows become infective
When do ascaris suum eggs become infective
2 weeks
Geomydoecus heaneyi: generic name, host
Chewing louse
1 species of gopher = Llano pocket gopher
Eimeria onychomysis: type of parasite, host genus
Coccidian
3 known species of grasshopper mice = Onychomys genus
Trichostrongylus axei: type of parasite, different hosts
Stomach hair worm
Adults in abomasum of ruminants + stomach of horses/swine/humans/rabbits
Disease caused by toxoplasma gondii
Toxoplasmosis
Toxoplasma gondii: definitive hosts, intermediate hosts
Definitive = sexual stages restricted to hosts in family Felidae (only felids can shed oocysts produced via sexual reproduction)
Intermediate = mammals and birds
Disease caused by schistosoma japonicum
Schistosomiasis
Schistosoma japonicum: definitive and intermediate hosts
Definitive = rodents, Carnivora, ungulates, primates
Intermediate = snails in genus Oncomelania
Disease caused by plasmodium reichenowi
Malaria
Plasmodium reichenowi: definitive and intermediate hosts
Definitive = mosquitos in genus Anopheles
Intermediate = chimpanzees
