Introduction to Course Flashcards
Why parasitology?
- heavy representation: 30% OF EUKARYOTES ARE PARASITIC! (60% of nematodes, 40% of insects)
- many relevant diseases of animals & humans
- 50% CLINIC PROFITS from dispensing fees, HALF OF THESE ARE FROM PARASITICIDES
What can parasites affect?
- clinical disease
- sub-clinical disease / reduced production
- aesthetics / human animal bond
- animal welfare
- public health
- money
How productive are parasites?
very
- single female of H. contortus (barber’s pole worm) can produce up to 10,000 eggs/day
- it can suck up to 0.05 mL of blood per day (1000 female = 500ML)
- average 1mo lamb: 12kg = 50mL/kg = 600 mL
What can parasites survive?
harsh conditions
- Trichinella - case in US after eating undercooked SK bear meat
- meat was frozen for 45 days & they still got infected
What can parasites be resistant to?
- parasites can develop resistance to drugs used to treat them (ex: malaria (Plasmodium genus), Ru nematodes, Ancylostoma in Ca
Who can parasites cause financial losses to?
Industry & small-scale producers
- production losses in cattle: 74 million pounds per year in UK (exclusive of veterinary car)
- largest animal health cost in Australian sheep industry ($11/ewe)
- most prevalent disease reported by US sheep farmers
What can parasites control?
Brains
- Dicrocoelium dendriticum (lancet liver fluke) is a parasitic worm that can manipulate ants into-zombie-like behaviour, climbing to the top of grass stalks & exposing themselves to the herbivore host
what is symbiosis?
Relationship btwn two organisms in close association with each other
What is mutualism?
- relationship btwn two organisms where both benefit (Ex: bacteria inside the rumen)
What is commensalism?
- relationship btwn two organisms where one organism benefits and the other doesn’t benefit but also isnt harmed (ex: amoeba inside the cecum/colon of cattle & sheep)
What is parasitism?
- relationship btwn two organisms where one benefits and the other is harmed
What is the definition of parasitism?
an ecological relationship where the parasite:
- depends on the host for survival & benefits from the host
- has negative effects on the host
- has greater fecundity than the host
- has an over-dispersed host distribution
What are endoparasites?
internal, causing infections
What are ectoparasites?
external, causing infestations
What kind of distribution do parasites have?
overdispersed distribution
- a lot of hosts have zero or a few parasites while a few hosts have
a lot of parasites (20:80 rule)
Why can an overdispersed distribution of parasites be a challenge?
it can be challenging to test for in a herd or flock
How do hosts differ?
- age, immune status, sex, size, genetics, resistance/resilience, behaviour, metabolism (insect attractants!), clinical presentation
What 3 things do you need for parasitism?
environment, hosts, parasites
What is the infective stage?
life cycle stage infective (can cause disease in) for host
What is the shed stage?
stages that are passed by the host
What is pre-patent period (PPP)?
time btwn infection & shedding of the next generation of parasites
What is the patent period (patency)?
period of shedding
What is prevalence?
proportion of infected hosts (like 1 out of 10)
What is the intensity?
the number of parasites per host (often expressed by proxy of fecal egg counts)
What is host specificity?
how restricted a parasite is to certain host spp (how picky it is!)
What is a direct life cycle?
Shed stages -> go into environment (EE) -> become infective stages -> go into definitive host (DH) and live there as adult parasite until reproduction & shedding
What is an indirect life cycle?
Shed stages -> go into environment (EE) -> go into intermediate host(s) & live there as a juvenile stages (no sexual reproduction, may be asexual reproduction) -> then go into definitive host (DH) and live there as adult parasite until reproduction & shedding
How can hosts be classified?
- definitive host (DH)
- intermediate host (IH)
- paratenic host
- vector
- transport
What is a definitive host?
- obligatory for ALL parasites (need this host to survive/reproduce)
- the only host in a direct life cycle
- if endoparasite undergoes sexual reproduction (helminths & coccidian protozoans), it occurs inside the DH
What is an intermediate host?
- obligatory for endoparasites w/ indirect life cycles - all cestodes & trematodes, some nematodes & protozoans
- parasite undergoes development w/in IH (NEVER sexual reproduction; sometimes asexual reproduction (amplification))
What is a paratenic host?
- HELPFUL FOR TRANSMISSION, BUT NOT REQUIRED (facultative vs obligatory)
- infection but no reproduction, no development
What is a vector host?
MOBILE transport host, often an arthropod. can be biological, in which the pathogen undergoes development or amplification, or simply mechanical. many ectoparasites are vectors (ex: ticks); some endoparasites (ex: heartworm, malaria) are vector-borne
What is a transport host?
- HELPFUL FOR TRANSMISSION BUT NOT REQUIRED (facultative vs obligatory)
- no infection, simply mechanical transport
What is an oocyst?
- a hardy, tick-walled spore, able to survive for lengthy periods outside a host
- organisms that create oocysts include Eimeria, Isospora, Cryptosporidium, Toxoplasma
What are sporozoites?
infective cell form
What is a trophozoite?
- G. nourishment
- intracellular stage that feeds & grows
What is a hypnozoite?
- G. sleep
- quiescent stage
What is a bradyzoite?
- G. bradys = slow
- slow-growing form responsible for parasitic infections
What is a tachyzoite?
- G. tachys = fast
- rapid growth & replication
What are the types of asexual reproduction performed by parasites?
- binary fission
- schizogony
What is schizogony?
trophozoites grow super large, while the nucleus divides many times, the structure is called SCHIZONT & when mature, the organisms are called MEROZOITES
What type of sexual reproduction is performed by parasites?
gametogony
