Lecture 2: Life Cycles Flashcards
Definitive host (endoparasites)
Host in which adult or sexually reproductive, stages of the parasite occur
Intermediate host (endoparasites)
Host required for parasite development but in which parasite does NOT become sexually mature
Paratenic host
Host in which the parasite does not undergo any required development but in which it remains alive and infective to another host
Direct life cycle includes a ____ host but no ___ host
Includes a definitive host but no intermediate host
What is a monoxenous parasite
Parasite with direct life cycles
Are nematodes and Protozoa monoxenous and heteroxenous
Monoxenous
What are the two infective stages of a direct life cycle
Resting and active stage
Are nematode eggs and protozoan cysts part of the resting stage or active stage for direct life cycle
Resting
What is the mode of transmission for resting stage for direct life cycle
Ingestion
Are nematode larva and protozoan trophozoite resting or active stage in direct life cycles
Active
What is the mode of transmission in active stage of direct life cycle
Ingestion, penetration of skin, direct contact
Does an indirect life cycle require an intermediate host?
Yes!
Do monoxenous or heteroxenous parasites have an indirect life cycle
Heteroxenous
T or F: all trematodes, tapeworms and many parasitic nematodes and Protozoa are monoxenous
False! These are all heteroxenous
What are the two infective stages of an indirect life cycle
Resting and active
Is an encysted larvae in the resting infective stage for indirect life cycle or active stage
Resting
What is the mode of transmission for resting stage indirect life cycle
Ingestion
Are helminth larva and protozoan trophozite in active or resting infective stage
Active
What is the mode of transmission for parasites in active stage indirect life cycle
Penetration of the skin, via a vector
Describe the basic pathway of direct life cycle
- Animal ingest infective egg
- Larvae are established in the small intestine and become patent over a specific period of time
- Unembryonated eggs passed in feces
- Cycle repeats
Describe the basic indirect life cycle
- Parasite infects or is ingested by intermediate host
- Intermediate host is either ingested by definitive host or bites definitive host
- Definitive host gets parasite
Are paratenic host required for completion of parasites life cycle
No!
What is the main role of paratenic host
Facilitates transmission to definitive host
What is stephanurus denatatus
Swine kidney worm
Is stephanurus dentatus monoxenous or heteroxenous
Monoxenous nematode
What nematode do earthworms act as paratenic hosts and how does this work
Earthworms are paratenic host for Stephanurus dentatus (swine kidney worm)
Paratenic hosts facilitate transmission so definitive host will ingest earthworm and therefore S. dentatus
What are the 4 modes of transmission for stephanurus denatatus
- Ingestion of free infective larvae (main mode)
- Ingestion of earthworm (paratenic host) carrying infective larvae
- Penetration of skin by infective larvae
- Transplacental transmission
Arthropod ectoparasites serve as ____ and ___
Parasites and vectors
What are the two main life cycles for ectoparasites
- Holometabolous (complete) metamorphosis
- Hemimetabolous (incomplete, simple) metamorphosis
What is holometabolous metamorphosis
Egg—> larva—> pupa—> adult
Which type of ectoparasites metomorphosis has differing larval and adult morphology
Holometabolous
What is hemimetabolous metamorphosis
Egg—> larva—> nymph—> adult
OR
egg—> nymph—> adult
Which type of ectoparasites metamorphosis has similar larval and adult morphology
Hemimetabolous
Are fleas and dipeterans holometabolous or hemimetabolous
Holometabolous
Are ticks, mites and lice holometabolous or hemimetabolous
Hemimetabolous
What 6 key points can we gain from life cycles of parasites
- Mode of transmission to host
- Stage infecting/infesting the host
- Predilection site of adult stage in/on host
- Route of predilection site
- Mode of exit from host
- Stage exiting host
What is dirofilaria immitis
Canine heartworm
What is the mode of transmission for dirofilaria immitis
Vectored by mosquitoes (Culex, aedes, anopheles)
What is the infective stage for dirofilaria immitis
Third stage larva (L3); migrates through mosquito bite wound
What is the predilection site of adult with dirofilaria immitis
Pulmonary arteries, right ventricle
What is the route to the predilection site for dirofilaria immitis
Venous circulation (from subcutis and abdominal/thoracic muscles)
What is the mode of exit for dirofilaria immitis
Blood ingested by mosquito
What is the exiting/diagnostic stage for dirofilaria immitis
Microfilaria in the blood
Ascaris suum causes what pathology to the liver and lung
Milk spots to liver and severe lung damage
How can the pathology caused by Ascaris suum in the lungs, liver and small intestine be helpful in identifying life cycle and treatment
Milk spots in liver:LARVAE- migrating through liver causing hemorrhage, fibrosis and lymphocyte infiltration
Lung damage: LARVAE- migrating causing hemorrhage, eosinophilic infiltration, edema, pneumonia
Small intestine: MATURING AND ADULT WORMS- cause inflammation, diarrhea, perforate small intestine, loss of nutrients
What is the prepatent period
Time between infection of definitive host and the appearance of the stage exiting the host
What stage/how would parasite appear during prepatent period
Egg, cyst
What is the best method to control life cycles during prepatent period
Deworming
What are some different locations where parasite stages can occur external to the host
Soil, water, vegetation, intermediate host
What environmental conditions promote development of survival stages
Temperature, humidity, shade
How can you use the environment to control and prevent parasitic diseases
Exposure to intense sunlight, suboptimal temperatures (temps below 15 degrees Celsius decrease egg survival)
What type of parasite usually only occur in 1 host species
Many lice
What type of parasites can occur in more than 1 host species but are restricted to family or species
Coccidia
What type of parasite can occur in more than 1 family or orders or hosts
Trichostrongylus axei
what are 3 examples of parasites with indirect lifecycles that can have varying host specificity at different stages
- Toxoplasma gondii
- Schisotosoma japonicum
- Plasmodium reichenowi
What is the definitive host for toxoplasma gondii
Felids
What is the intermediate host for toxoplasma gondii
Mammals and birds (broad host range)
What is the definitive host for schistosoma japonicum
Rodents, carnivores, ungulates, primates and other mammals (broad host range)
What is the intermediate host for schistosoma japonicum
Snails in the genus oncomelania (narrow host range)
What is plasmodium reichenowi
Malaria
What is the definitive host for plasmodium reichenowi
Mosquitoes in the genus anopheles (narrow host range)
What is the intermediate host for plasmodium reichenowi
Chimpanzees (narrow host range)
Why is it important to know the life cycle
- Diagnose disease and ID parasite
- Predict what pathogenic changes occurs
- Optimize treatment to improve control (which animals to treat/when to treat)
- Develop environmental control programs
- Reduce cross-species (including zoonotic) infections
