Parasites: general concepts and ectoparasites Flashcards
Facultative parasite
organism that may become a parasite, but does not require a host for completion of its life cycle.
Example of facultative parasites
occur among many species of fungi:
- Blastomyces dermatitidis
- Blastomycosis
Opportunistic infection
infection caused by pathogens (bacteria, viruses, fungi or protozoa) that take advantage of an opportunity not normally available, such as:
- host with weakened immune system
- breached integumentary barriers
- altered microbiota
Parasitism
when an organism for all or part of its life, derives at least some, but not often all of its food from a living organism of another species (Host), usually living in or on the body or cells of the host, which is usually harmed to some extent by the association.
- ONE WHO EATS AT ANOTHER’S TABLE
Ectoparasite
live on the outside of the host
Endoparasite
live on the inside of the host
Epibiosis
any relationship between two organisms in which one grows on the other but is not parasitic on it
Phoresis
is a non-permanent, commensalistic interaction in which one organism attaches itself to another (the host) solely for the purpose of travel.
Epibiosis and phoresis
- The act of being carried
- In this case the organism or symbionts are nutritionally independent of each other and have a facultative association ( non-obligatory).
Commensalism
- Latin com mensa meaning “sharing a table”
- this occur when a smaller symbiont, the commensal, feeds on the food available in or on the surface of the host, for whom it is unusable or unwanted, while the host neither benefits nor is harmed.
Ht - x —> X
Parasitism
Ht+- 0 (- x)
Commensalism
Ht + Y
Mutualism
(symbiosis - long-term)
Ht
Host table complex (food available)
Helminths
- parasitic worms, large and multicellular
- includes a number a of phyla, many which are unrelated (phylogenetically) but they have superficial similarities:
- They are vermiform or “worm-like” in form
Phyla in Helminths
- Phylum Nematoda (roundworms)
- Phylum Platyhelminthes (flatworms)
- Phylum Acanthocephala (thorny-headed worms)
- Phylum Annelida (segmented worms) not parasites (leeches)
Classes of the Phylum Platyhelminthes
- Class Cestoda (tapeworm)
- Class Trematoda (flukes: endoparasites)
- Class Monogenea (skin flukes: ectoparasites)
- Class Turbellaria (free-living flatworms, some parasitic forms)
Parasites of veterinary importance
- Helminths
- Kingdom Protozoa (Protist)
- Kingdom of Fungi
- Kingdom Animalia
Phylum of Kingdom of Protozoa (Protist)
- Phylum Mastigophora (flagellates)
- Phylum Apicomplexa
- Phylum Ciliophora (ciliates)
Phylum of Kingdom of Animalia
- Phylum Arthropoda (insects/arachnids, copepods)
- Phylum Cnidaria (Myxozoa)
Parasites
- Live in or on the host
- Smaller than their host
- Parasites reduce host biological fitness to some extend (pathogenicity/virulence)
- Typically don’t kill their host
- Reproduce at a faster rate than their host
Parasites use host for survival
EXAMPLES
- Food
- Water
- Heat
- Habitat
- Transmission
Mode of infection
- Oral
- Skin penetration
-Injection - Transplacental (vertical transmission)
examples of oral mode of infection
- Spore in environment
- Oocyst/eggs in environment
- Larvae in environment
- Larvae in intermediate host, paratenic host
- Cyst in other host
- Larvae in milk
Types of host
- Definitive host
- Intermediate host (IH)
- Paratenic host (PH) or transport host
- Aberrant or abnormal host
- Dead-end or incidental host
Intermediate host (IH)
- Required
- serves as a temporary but necessary host for continued development of essential life stages
Paratenic host (PH) or transport host
NON-REQUIRED transport “intermediate” host in which no development of the parasite occurs
Aberrant or abnormal host
- Host not usually used by the parasite
- Development slow or incomplete
Dead-end or incidental host
An “intermediate” host that generally does not allow transmission to the definitive host , thereby preventing the parasite from completing its development
Direct life cycle
- only one host required to complete the life cycle
- stages in this host and the environment
- Host specific or broad host spectrum (non-specific)
- Definitive host (DH)
- parasites that (sexually) reproduce without an intermediate host have direct life cycle
Definitive host
where sexual reproduction takes place
Indirect life cycle
- two or more host required to complete the life cycle
- Host specific or broad host spectrum (non-specific)
- Final Host (FH): sexual reproduction (DH)
- Intermediate host (IH)
- Involves stages in the hosts and the environment
Sexual reproduction
- Genetic diversity
- Longer life cycle
- Must have at least 2 parasites (M & F)
Asexual reproduction
- Lack of genetic diversity
- Short life cycle
- One is enough
Benefits the parasite gains from the host
- Survival: heat, food, water, habitat
- Food: blood, mucosal lining etc.
- Transmission or maturation / reproduction
- Arrested development/ hypobiotic stage
Hypobiosis
- A state of reduced metabolic activity
- term most often used for arrested development that has a seasonal basis (nematodes). Can also be caused by host immune responses and an overcrowding effect, high numbers of adults inhibit larvae
Habitat and food: Where in the host?
- Predilection site
- Aberrant site
Predilection site
- preferred site in or on the host
- food sources, able to avoid immune systems (for at least some time period)
- Feeding and location related to pathology
Aberrant site
site in or on a host which is not a normal location
Complex life cycle
trophic transmission
