Introduction to Structures & Life Cycle Stages Flashcards
what are the 3 categories of helminths?
- nematodes
- cestodes
- trematodes
What are nematodes?
roundworms
What are cestodes?
tapeworms
what are trematodes?
flukes
What phylum do cestodes & trematodes belong to?
Platyhelminthes (flatworms)
Defining features of a nematode?
tubes & tails
What important structures do nematodes have on their head ends?
alae, buccal capsule, teeth, pharynx
What important cuticular structures are in the male nematode’s tail?
copulatory bursa with finger-like structures called bursal rays, cloaca, spicules, vas deferens, testis, asymmetric dorsal lobe
What are the basic features of nematodes?
- parasitic & free-living stages & spp
- tiny (less than 1 mm) to enormous (1 m)
- separate sexes (dioecious), sexual reproduction w/in definitive host (DH)
- eggs (oviparous), larvated eggs (ovoviviparous), or larvae (viviparous)
- direct & indirect life cycles
- host & tissue specificity
- larvae can undergo complicated migrations & cause pathology
Direct life cycle of a nematode?
Eggs hatch in the external enviro -> first stage larvae (L1) -> moult -> 2nd stage larvae (L2) -> moult (translation) -> 3rd stage larvae (L3) is ensheathed -> moult & move into host as 4th stage larvae (L4) -> moult -> adults -> mate -> eggs
Defining features of a cestode?
hooks & segments (hooks present in eggs & larvae also)
What is the structure of a cyclophyllid (order cyclophyllidea) cestode?
- head or scolex with 4 suckers & a rostellum w/ hooks for attachment to host
- neck
- body (strobila) w/ immature segments, mature segments, & gravid segments from cranial to caudal
segment aka proglottid
What are the basic features of cestodes?
- all spp are parasitic (need a host) & hermaphroditic (can reproduce themselves)
- some tiny (2 mm), some enormous (12 m+)
- transmission is by INGESTION (DH ingests IH, IH ingests eggs)
- ALL HAVE INDIRECT LIFE CYCLE w/ intermediate host
- adults in DH parasitize the GI system, MAY cause a few problems (not v pathogenic), & produce eggs immediately infective
- larval stages in tissues of IH may cause serious problems
- asexual reproduction (amplification) may occur
- we will focus mostly on cyclophyllid cestodes except 1 pseudophyllid
What kind of life cycle do cestodes have and what do they need for it ?
- indirect life cycle w/ environmental stage
- need environment, direct host, indirect host, & parasite
What is the cyclophyllid cestode life cycle?
egg w/ hexacanth larvae passes out of the host & into the external environment via the feces -> this egg is ingested by the intermediate host -> hatches -> HEXACANT LARVAE develop into METACESTODE w/ 1 or more protoscolices -> intermediate host is ingested by definitive host where protoscolices develop into scolex in adults -> eggs are formed
What are the different types of cyclophyllid metacestode larvae?
- Cysticercoid - single protoscolex
- Coenurus - multiple protoscolices
- Cystic hydatid - multiple protoscolices, feels like sand inside when opened
- Cysticerus - single protoscolex & a bladder
What are the defining features of trematodes (Class Digenea)?
snails & suckers
important features in trematode structure?
- mouth, oral sucker, pharynx, esophagus, genital atrium, acetabulum or ventral sucker, excretory vesicle, seminal vesicle, vitelline glands, vitelline duct, uterus, vas deferens, ovary, oviduct, seminal receptacle, ootype, vitelline reservior, testes, Mehlis’ gland, nephridiopore
What are the basic features of trematodes?
- ALL PARASITIC
- from tiny (<1 mm) to giant (10 cm)
- MOST ARE HERMAPHRODITIC (EXCEPT SCHISTOSOMES)
- sexual reproduction occurs in DH
- all have an indirect life cycle w/ intermediate host(s) (first IH is always a gastropod (slug or snail) where asexual reproduction occurs)
- adults in DH parasitize GIT or lungs; often pathogenic
- larval stages in IH parasitize many tissues; can be pathogenic (snail castrators, zombie ants)
What kind of life cycle do trematodes have and what do they need for it ?
- indirect life cycle w/ 2 intermediate hosts
- need appropriate environment, IH #1 (snail), IH #2, DH mammal, and the parasite
What is the basic life cycle of trematodes?
egg containing morula is passed in the feces into the external environment (usually H2O) -> morula develops into a miracidium -> hatches (sheds it’s capsule) -> miracidium penetrates the foot of the 1st intermediate host (snail) -> asexual reproduction & development through several stages occurs here -> goes into IH 2 or vegetation as a metacercaria larvae -> ingested into definitive host as adult -> has eggs
Size of nematodes?
<1mm - 1m
Size of cestodes?
2 mm to 12 m
size of trematodes?
1 mm to 10 cm
parasitism in nematodes?
MANY are parasites
parasitism in cestodes?
all parasitic
parasitism in trematodes?
all parasitic
sex in nematodes?
dioecious (separate sexes)
sex in cestodes?
hermaphroditic
sex in trematodes?
most hermaphroditic (except schistosomes)
reproduction in nematodes?
sexual reproduction in definitive host; producing eggs, larvated eggs or larvae
reproduction in cestodes?
sexual in definitive host; and asexual in intermediate host (amplification)
reproduction in trematodes?
sexual in definitive host; asexual in intermediate host
what is the life cycle of nematodes?
direct or indirect
what is the life cycle of cestodes?
indirect
what is the life cycle of trematodes?
indirect; involves a gastropod & may involve another intermediate host
what is the pathogenicity of nematodes?
variable - larvae can undergo migration, adults can suck blood
what is the pathogenicity of cestodes?
- ADULTS IN DEFINITIVE HOST - MAY cause a few symptoms
- LARVAL TISSUE STAGES IN INTERMEDIATE HOST may cause serious problems
what is the pathogenicity of trematodes?
- ADULTS IN DEFINITIVE HOST: GI, lungs, kidneys, liver, often pathogenic
- LARVAE IN INTERMEDIATE HOST - can be pathogenic (snail castrators, zombie ants
What are arthropod parasites?
- bugs
- fleas
- flies
- lice
- mites
- ticks
What are the important groups & orders of parasitic arthropods?
Arachnida
- mites & ticks (Subclass Acari)
Insecta
- bugs (O. Hemiptera), lice (O. Phthiraptera: Sub O. Mallophaga (now Ischnocera), Sub O. Anoplura)
- fleas (O. Siphonoptera)
- flies (O. Diptera)
Important characteristics of mites?
- dorso-ventrally flattened
- LARVA: 6 legs, NYMPH & ADULT: 8 legs
- variable host specificity
- microscopic (<1mm)
What are the two types of mites?
- burrowing mites (Short legs, round body)
- surface mites (long legs, oval body; pretarsus: sucker or caruncle, pedicle (short or long, segmented or not)
What is the basic life cycle of a mite?
- entirely on the host
- eggs -> larvae -> nymphs -> adults -> lay eggs
- complete in 10-14 days
Important characteris-ticks?
- dorso-ventrally flattened
- larva: 6 legs, nymph & adult: 8 legs
- variable host specificity
- macroscopic (3-12 mm)
What are the two types of ticks?
- hard ticks (Family Ixodidae) - high vetmed relevance; vectors for viruses, bacteria, protozoa, nematodes in humans/animals; tick paralysis; toxicosis
- soft ticks (Family Argasidae) - only 1 soft tick of relevance for this course
What is the generic life cycle of a tick?
- On host 1: male & female adult ticks mate -> female lays eggs in the environment -> eggs hatch into larvae -> larvae go onto host 2: take a blood meal -> go back into enviro & molt to nymph -> nymph goes onto host 3: takes a blood meal -> goes back into the enviro & molts to adult
- life cycle length takes 8 weeks to 2-3 yrs (host-dependent)
What are some important characteris-ticks of hard ticks (Ixodidae)?
- sexual dimorphism is obvious (males have a scutum over their whole back while females only have an anterior scutum)
- the scutum can be ornate or inornate
- festoons may be present
- the capitulum varies in shape & size of mouthparts
- the ventral anal groove may or may not extend anteriorly around the anus (defining characteristic)
What are lice and what are their 3 body segments?
- insects
- w/ head, thorax, & abdomen
what are the important characteristics of lice?
- dorso-ventrally flattened
- 1-8 mm
- 6 legs as adults, no wings
- extremely host specific
What are the two types of lice?
- Mallophaga (Ischnocera) - chewing/biting lice (feed on skin; head is wider than thorax, yellow in colour)
- Anoplura - sucking lice (blood feeder; head narrower than thorax; shorter first pair of legs; gray to dusky red in colour)
What is the life cycle of lice?
- occurs only on host
- eggs (nits) -> nymphs (Feed on blood or dander) -> adults (feed on blood or dander) -> lay eggs
- ~ 3 weeks in length
Important characteristics of fleas?
- laterally flattened
- 6 legs, last pair very well developed for jumping
- not host specific
- differentiation of spp based on presence of pronotal (mullet) & genal (mustache) combs, shape of head, & spines
What is the life cycle of fleas?
- eggs in environment -> larvae in environment -> pupae in environment -> adults on host
- takes at least 3 weeks
- complete metamorphosis
What are the groups of flies?
- Nematocera
- mosquitoes
- blackflies
- midges - brachycera
- horseflies
- deerflies - cyclorhapha
- faceflies
- hornflies
- botflies
TIME TO COMPLETE LIFE CYCLES IS HIGHLY VARIABLE, DEPENDING ON SP & ENVIRONMENT
What are the informal classifications of flies, when are they most important, and why do we care?
- biting flies
- secretion feeding flies
- myiasis flies
- mostly important for large animal
- differentiating btwn these is important b/c they differ in pathogenesis, pathogen transmission, & management implications
What are biting flies?
mosquitoes, midges, horse flies, stable flies, sand flies
What are secretion feeding flies?
face flies
What are myiasis flies?
- OBLIGATE PARASITES: larvae MUST develop in a live host (bots/warbles (oestrids), maggots ex: screw worms)
- FACULTATIVE PARASITES: larvae MAY opportunistically develop in a live host (maggots ex: blowflies)
What class are mites?
arachnida
What class are ticks?
arachnida
what class are lice?
insecta
What class are fleas?
insecta
Do mites have wings?
no
do ticks have wings?
no
do lice have wings?
no
do fleas have wings?
no
How many legs do mites have?
6 (larva), 8 (nymphs/adults)
How many legs do ticks have?
6 (larva), 8 (nymphs/adults)
How many legs do lice have?
6 (adults)
How many legs do fleas have?
6, last pair is well-developed for jumping
how big are mites?
< 1mm
how big are ticks?
3-12 mm
how big are lice?
1-8 mm
how big are fleas?
1-4 mm
Body shape of mites?
dorso-ventrally flattened
Body shape of ticks?
dorso-ventrally flattened
Body shape of lice?
dorso-ventrally flattened; have a head, thorax, & abdomen
Body shape of fleas?
laterally flattened; no clear separation of body segments
are mites host specific?
variable hosts
are ticks host specific?
variable hosts
are lice host specific?
yes!
are fleas host specific?
no!
What are the important taxonomic groups of parasitic protozoa?
- Phylum: Sarcomastigophora (moves by flagella or pseudopodia)
- Phylum: Apicomplexa (has an apical organelle used to penetrate host cell)
What are the groups in Sarcomastigophora?
- sarcodina
- mastigophora
What is sarcodina?
- amoeboid movement (pseudopodia)
- direct lifecycles
- ex: Entamoeba
What is mastigophora?
- 1 or more flagella(e)
- direct or indirect lifecycles
- ex: Leishmania, Trypanosoma, Histomonas, Giardia, Tritrichomonas
What are the groups in Apicomplexa?
- Coccidia
- Piroplasmidia
- Haemosporidia
What is coccidia?
- obligate intracellular parasites
- sexual & asexual reproduction
- environmentally resistant oocysts/sporocysts
- direct/indirect lifecycles
- ex: Eimeria, Toxoplasma, Neospora, Sarcocystis, Cystoisospora, Hammondia, Cryptosporidium
What is piroplasmidia?
- parasites of blood cells
- sexual reproduction occurs in vectors (TICKS)
- indirect lifecycles
-ex: Babesia, Theileria, Cytauxzoon, Hepatozoon
What is Haemosporidia?
- parasites of blood cells
- sexual reproduction occurs in vectors (BLOOD SUCKING DIPTERANS)
- indirect lifecycles
- ex: Plasmodium
What is a mucosoflagellate’s direct life cycle?
ex: giardia
Trophozoite in host (asexual reproduction on mucosa) -> cysts are shed in feces -> cysts in environment -> cysts ingested -> develop into trophozoites in host
What is the lifecycles of Cystoisospora felis
Sporulated oocyst in the environment (2 sporocysts, 4 sporozoites) -> ingested by host (cat) -> sporozoites move into intestinal epithelial cells -> formation of microgametes (male) & macrogamonts (female) -> microgametes invade macrogamonts -> zygote -> unsporulated oocysts are shed in feces -> become sporulated oocysts
What is merogony?
asexual multiplication w/ a defined # of “generations” for each spp
How do apicomplexans reproduce?
- alternate ASEXUAL & SEXUAL
- merogany (Asexual) - intestine of definitive host: mother cell (meront) in intestinal epithelium produces merozoites; w/in intermediate host: tissue cyst forming coccidia: fast dividing tachyzoites (systematic), slow dividing bradyzoites (w/in tissue cysts)
- gametogony (sexual) - formation of gametes in intestinal epithelium (macrogametocyte: female; microgametocyte: male; sexual reproduction leads to fertilized zygote)
- sporogony: zygote divides into sporozoites, infective for next host; in environment or intestines of definitive host, depending on parasite spp
