Parasitology (introduction, nematodes) Flashcards
What is a parasite?
An organism that lives in or on another living organism (host), obtaining from it part or all of its nutrients.
What are the 4 main classes of parasites?
Protozoa
Arthropods
Platyhelminthes
Nematoda
What are simple (direct) life cycles?
Only have one host during its life cycle
What are complex (indirect) life cycle?
Have 2 or more hosts during its life cycle
What is a definitive/final host?
Host in which sexual reproduction takes place
What is an intermediate host?
Host in which only immature stages grow & develop. Asexual reproduction may or may not occur. Blood meal is required from host to develop
What is a paratenic host?
Host not required to complete the life cycle but help parasite to get to the host. Blood meal not needed because they are just used as transport
What is considered a normal host?
An animal recognized as part of the normal life cycle.
What is considered an abnormal or aberrant host (dead-end)?
Animal not normally used as a host
Often associated with disease (not always)
Animal could be an abnormal definitive, intermediate or transport host, depending on which stage of the parasite life cycle or is present
What is considered a reservoir host
Host serves as a source of infection for other animals
What is a considered a biological vector?
Parasite develops in the vector and transmits infectious disease
What is a considered a mechanical vector?
A contaminated instrument that transmits infectious disease
Where’s a endoparasite located in a host and what do they cause?
Inside the host
Cause infection
Where’s an ectoparasite located in a host and what do they cause?
Outside of the host
Cause infestations
What is the difference between a micro parasite and a macroparasite?
Microparasites multiply inside the host while macroparasites don’t multiply at all
What does infectious mean?
Caused or capable of being communicated by infection
What does infective mean?
Parasite stage capable of infecting the host
What does prepatent period mean?
The period from infection until the sexual maturity of the parasite
Mainly associated with macroparasites
Ex: heartworm has a 6 month prepatent period.
What does patency period mean?
The complete life span of an adult parasite
It is an ongoing cycle
What determines outcomes of the host-parasite relationship?
Infection/infestation
Parasite usually requires appropriate stimulus to recognize potential host
Host immune response
What 3 factors does pathogenesis depend on?
1) the status of host defenses
2) number of parasites present (+/- virulence)
3) pathogenicity of those parasites
Pathology from parasitic infection may be the result of what?
1) trauma to cells, tissues, &/or organs
2) changes in cellular growth patterns
3) interference with host nutrient acquisition
4) toxins released
5) host immune response to infection
What does it mean when parasite populations in animals are aggregated (over dispersed)?
Not each member of a group will be infected equally
Not evenly dispersed through the main group
What is the 70-30 rule?
The top 30% of a given group will have 70% of the parasitic infection while the bottom 70% will have 30% of the parasitic infection
How do we diagnose parasites?
Morphologic (microscopic and gross examination of blood, feces, tissue and remains
Immunologic assays
Molecular tests (PCR)
What are the general characteristics of helminths (worms)
Macroparasite
Often highly host specific in the definitive host either oviparus or ovoviviparous
Fecal oral or environmental-oral
What are the two phylum of helminths?
Nematoda & platyhelminthes
What are the general characteristics of the phylum nematoda?
Non-segmented, cylindrical, tapered at both ends
Most successful parasite of all the worms
Many are free living in the soil
Major plant and animal parasite
Range in size
Cuticle present and is flexible but not metabolically active & is a secondary sexual structure
Body wall as muscles for movement
Can sensing environment
Neurotransmitter
What are the general characteristics of nematoda digestion?
Buccaneers capsule-oral opening
Esophagus
Intestine
What are the general characteristics of nematoda reproduction?
Sexual dimorphism
Males have spicules
Females produce eggs or larvae
What is the diagnostic stage of most nematodes?
Females producing eggs or larvae
Why do nematodes need to molt?
Cuticle restricts growth
How many molts do nematodes generally go through?
4
What is the L3 rule?
The infective stage for nematodes is almost always L3
What are the 4 superfamilies of strongylida?
Trichostrongyles
Strongyles
Hookworms
Metastrongyles
What are the characteristics of strongylida?
Bursa
Usually found in the GI tract
Cause tissue damage
Feed on blood or tissue
What are the characteristics of strongylida eggs?
Oval, thin shell & contain a morula
What are the characteristics of the strongylida L3 larvae?
Retained cutical from L2 as a sheeth
Uses nutrients stored from L1 & L2
Need high temperatures and moisture to develop faster
What is hypobiosis?
Larvae become dormant in host GI tissue site & the resumes development to adult at a later time
It’s an adaptation mechanism for optimizing chances of survival
What are the parasites that undergo hypobiosis in the L3 larval stage?
Trichostrongylus
Ancylostoma
Cyathastominae
What are the parasites that undergo hypobiosis in the L4 larval stage?
Ostertagia
Teladorsagia
Harmon hus
What are the 2 common stimuli for arrested development?
Environmental
Host immunity
What is “periparturition egg-rise”
2 weeks from parturition to 1 week after, immunity in GImtract is decreases due to immunity being focused on baby and this allows the parasite numbers to increase
What is the life cycle of Trichostrongyloida?
1) host ingests L3 stage
2) L3 molts to L4 in the GI tract
3) adults feed and reproduce in host
4) parasite exits host
5) larvae grow & molt in environment until L3 and ingested by host
Where are trichostrongyles located in the host body and what species do they usually infect?
Abomasum in ruminants
What condition do trichostrongyloida induce?
Parasitic gastroenteritis
What is the most important helminths in cattle
Ostertagia ostertagi (brown stomach worm)
What is the most important helminths in small ruminants?
Haemonchus contortus (Barber’s pole worm)
Where do Ostertagia ostertagi go in the body and why?
The L3 larvae enter gastric glands for a couple of days to molt to L4
What is the most pathogenic stage of Ostertagia ostertagi and why?
L4 because it emerges from the gastric gland after hypobiosis because it damages the gland
What characteristic lesion does Ostertagia ostertagi produce and why is it important?
A lot of small nodules within the abomasum and it causes permanent destruction of gastric glands which fail to activate pepsinogen and the loss of bacteriostatic effects
What is the clinical importance of Ostertagia ostertagi?
Mainly affects young cattle
Causes diarrhea, weight loss, hypoproteinemia (bottle jaw), and death
What parasite is more pathogenic in sheep & goats?
Haemonchus contortus
What does Haemonchus contortus cause?
Anemia
Anorexia
Hypoproteinemia (bottle jaw)
Weight loss
Death
Why does Haemonchus not cause gastroenteritis in ruminants?
It is a blood sucker
What is the most pathogenic stage in osteragia?
L4
What stimulus has the most influence on the proportion of strongylid worms that become hypobiotic?
Weather conditions and host immune system
What are the general characteristics of strongyloidae
Parasite of GI tract
Large buccaneers capsule
Plug feeders
Most important helminths of horses
What are the 2 subfamilies of strongyloidae?
Cyathostominae (small strongyles)
Strongylinae (large strongyles)
Why are they referred to as “small strongyles” & “large strongyles”
Small has a smaller migration within the host
Large has a larger migration within the host
What is the disease called when there is a strongylidae infection?
Strongylidosis
What is the disease called when there is a strongylinae infection?
Strongylinosis
Once the cyathostomins L3 larvae has infected the host where does it migrate to?
Goes to the large intestine and penetrates the lumen to mature to L4 (hypobiosis) with a minimum prepatent period of 2-3 months where they will erupt and mature to adults
What stage of cyathostomins cause the most harm & what happens?
L4 (not the adult) and they erupt in the spring and cause nodules within the large intestinal lumen causing secondary infections
Can treatment of hypobiotic larvae kill them?
No because their metabolism is not active to consume the antihelminthic
What are the characteristics of chronic cyathostominosis (type 2)?
Gradual inflammation & thickening of the gut wall
Protein losing enteropathy
What are the clinical signs of chronic cyathostominosis (type 2)?
Intermittent diarrhea
Mild to moderate colic
Poor conditions
Hypoproteinemia
What are the characteristics of acute larval cyathostominosis (type 1)?
Rapid onset
Occurs when large number of arrested larvae synchronously emerge
What are the clinical signs of chronic cyathostominosis (type 2)?
Fever
Diarrhea that leads to dehydration
Edema which leads to hypoproteinemia
When are horses most susceptible to cyathostomins?
< 3-4 years of age
What is the most important parasite of the large strongyles?
Strongyles vulgaris
Explaine the larval migration of Strongyles vulgaris.
Following infection by L3, they molt into L4 which migrates through the arteries.
Once it reaches junction of cranial mesenteric artery & aorta.
They then return to large intestine about 4 months after infection
Occ. larvae migrate to other areas.
What is the prepatent period of Strongyles vulgaris?
6 months
What is the pathogenesis of Strongyles vulgaris/
Cause verminous arthritis/aneurysm
Larvae damage arterial vessels leading to thrombus which can reduce blood flow.
Portion of thrombus may break off and block blood flow leading to ischemia
What are the clinical signs of Strongylus vulgaris and how is it diagnoses
Colic
Abdominal pain
Death
Difficult to diagnose
What are the characteristics of Ancylostomatoidae (hookworms)?
Found in the small intestine of many small animals
Blood feeders via plug feeding
Teeth or cutting plates
What is the most important parasite of dogs in this region?
Ancylostomatidae (hookworms)
Specifically Ancylostoma caninum
Explain the life cycle of Ancylostoma caninum?
External— egg to L3 in soil
Dog infected by environment by L3 via skin penetration
After skin penetration larvae migrate to heart/lung and then either cough up, swallow, and develop in small intestine OR travel to tissues & become dormant & become active at the end of pregnancy & migrate to the mammary gland
Puppy then ingests the L3
What is larval leak?
When larvae reactivate from being dormant and go back to the small intestines and go through cycle again.
In pregnant female dogs how many pregnancies can hookworms infect for.
Up to 3 separate pregnancies
Egg laying hookworms in the intestine can come from where?
Skin penetration
Transmammary infection
Ingestion of L3
What is the pathogenesis of Ancylostoma caninum?
Low worm numbers= asymptomatic
Diarrhea
Anemia
Skin lesions
What is the main difference between Ancylostoma tubaeforme and Ancystoma caninum?
Ancylostoma tubaeforme very rarely cause perinatal transmission
Why are hookworms a concern for public health?
Larvae can penetrate human skin & cause cutaneous larva migrans
What are the characteristics of Metastrongyloidae (Metastrongyles)?
Parasite of lung, blood vessels & other tissues
Mostly diagnosed by larvae in feces not by eggs
Invertebrate is intermediate host (mollusk)
Not a major concern in domestic animals
True or false: in order to differentiate small from large strongyles we must measure the eggs in a fecal analysis?
False
What is the most important pathogenic mechanism in canine hookworm infection is
Anemia in puppies
What are the main characteristics of Ascrids order?
Bigger than most nematodes
Robust
GI tract
Roundworms
Direct life cycle in domestic animals
Highly successful parasite in all vertebrate classes
Where do the adult ascarids live & what do they feed on?
Live in the lumen of the small intestine & feed on lumen contents of host fluids, do not attach to the lumen wall
Females very prolific
What are the characteristics of Ascarid eggs?
Thick walled
Round
One cell inside
What is the life cycle of Ascarids?
Eggs passed in feces
Develop to infective stage (egg to L3) in 2-4 weeks
Egg is not infective until it’s is fully developed
The infective larva does not hatch until the egg is swallowed by a host
MIGHT have a migratory phase in the definitive host
What is the patent infection of Ascarids?
Eggs in feces
What are the characteristics of Parascaris equorum
Adults in small intestine
World wide distribution
Males: up to 30 cm
Females: up to 50 cm
What is the life cycle of equine ascrids?
Eggs passed in manure
Larvae hatch in intestine & penetrate wall
Hepatotracheal migration
Pre-patent period is about 3 months
What is hepatotracheal migration?
Parasite carried to liver in blood
Enter hepatic portal system
Reach lungs about 1 week PI
Coughed up & swallowed
Return to small intestine
What are Parascaris clinical signs?
Common in young horses
Adults in small intestine
Competition with host for nutrients
Poor condition rough hair coat, pot belly
Very heavy infection can lead to perforation or impaction
In the lungs they can lead to mechanical & inflammatory damage with nasal discharge
True or false: Parascaris don’t typically infect adults because they develop immunity?
True
What are the 2 ascarid genuses?
Toxocara canis
Toxocara cati
What are the routes of transmission of T. canis?
Ingestion of infected eggs
Transplacental
Transmammary infection
Paratenic hosts
What clinical signs do heavy toxocara canis burdens cause?
Diarrhea/ constipation
Colic & pot belly
Vomiting
Poor hair coat
Intestinal obstruction
Pneumonia
What is the biggest difference in T. cati life cycle compared to T. canis?
There is no transplacental transmission
Why are Toxocara of public health importance?
They are ingested and can cause visceral larva migran &/or ocular larva migrans
What are the zoonotic ascrids of importance?
Ascaris suus
Baylisascaris procyonis
T canis
T cati
