11 Microbial Diversity - Parasites Flashcards
Parasite
Organism that lives on or within a host and benefits at the host’s expense
Commensalism
one partner benefits, other is not hurt
Mutualism
Both partners benefit
Symbiosis
any 2 organisms living in close association, commonly one living in or on the body of the other, as symbiotic, as contrasted with free living
Facultative parasitism
When an organism can live free or establishes a parasitic existence depending on a host e.g. Ringworm
Obligatory parasitism
When an organism establishes a permanent parasitic existence and is completely dependent on the host e.g. Plasmodium, head lice.
Accidental or incidental parasitism
occasionally an organism parasitizes a species other than its usual host e.g. Hymenolepis diminuta (rat tape worm in man)
Three major groups of parasites
- Helminths (worms)
- Protozoa
- Arthropods
Helminths
Multicellular and visible to the naked eye
Types: Roundworms (e.g., Ascaris), flatworms (e.g., Schistosoma), tapeworms (e.g., Taenia)
Helminths life cycle
Typically involve both a definitive host (where the adult parasite reproduces) and an intermediate host (where larval or juvenile stages may develop)
Protozoa
Unicellular and usually microscopic.
Can cause diseases like malaria (Plasmodium), amoebic dysentery (Entamoeba histolytica).
Protozoa life cycle
Many protozoa have complex life cycles with asexual (e.g., binary fission) and sexual stages (e.g., gametogenesis)
Transmission may involve intermediate hosts, and infection often occurs through ingestion of cysts or vectors
Arthropods
Invertebrates with jointed limbs (e.g., ticks, fleas, mosquitoes)
Ectoparasites (live on the outside of the host)
Arthropods life cycle
Arthropod life cycles typically include egg, larval, nymph, and adult stages. Many arthropods are vectors, transmitting pathogens (e.g., protozoa, bacteria) from one host to another during feeding
Types of parasites (5)
- Endoparasites
- Ectoparasites
- Temporary parasite
- Permanent parasite
- Opportunistic parasite
Endoparasite
live within the host causing infection
Ectoparasite
live on the external surface of the host causing infestation
Temporary parasite
only visits the host to get its meal
Permanent parasite
always fixed to the host
Opportunistic parasite
produces disease only in immunodeficient hosts
Sources of parasitic infections
Water / soil / raw vegetables and fruit / animals / fish / vectors (arthropods) / blood
Modes of infection
Injection / inhalation / penetration of skin and mucous membrane / bites / direct contact / blood transfusions / sexual
How do parasites cause harm in its host?
Large number of parasites
Site of parasitism
Feeding habits
Competition for nutrients
Types of host (3)
Definitive Host - parasite reaches sexual maturity and reproduces
Intermediate Host - parasite develops but does not reach sexual maturity
Reservoir Host - harbors the parasite but may not show symptoms; acts as a source of infection for other hosts.
Direct transmission
parasite is passed from one host to another without the need for a vector
(e.g. direct contact, ingestion of infected material)
Vector borne transmission
parasite is transmitted by a vector organism, such as a mosquito or tick, that acts as an intermediary
(e.g. malaria, Lyme disease).
Zoonotic transmission
Transmitted between animals and humans
Pathogenicity
Ability of a parasite to cause disease in its host
This depends on the parasite’s ability to invade tissues, evade the immune system, and reproduce within the host.
Virulence
A measure of the severity or harmfulness of the parasite to the host, often related to how much damage the parasite causes
Life cycles of parasites (2)
- Simple - 1 host
- Complex - multiple hosts (sexual in 1 host and asexual in another)
Simple life cycles - direct
Parasite completes its entire life cycle in 1 host
Simple life cycles - asexual
In some cases parasites can reproduce asexually in the host
Complex life cycles - intermediate hosts
Asexual stages occur in the intermediate host before the parasite reaches sexual maturity in the definitive host
Complex life cycles - vector transmission
Arthropods or other organisms act as vectors, transmitting the parasite between hosts
Complex life cycles - larval stages
In helminths, larvae may infect an intermediate host, developing into cysts or larvae that are then consumed by the definitive host
