HOST - PARASITE RELATIONSHIP
Symbiosis - means living together in close association of two phylogenetically different
organisms, which are called the symbionts.
Symbiotic relationships can be characterized by specifying the nature of the interactions
between the symbionts.
1. Mutualism - Mutualism is a relationship in which the organisms both benefit from a
relationship with each other.
- The symbionts are called mutualists.
2. Commensalism - the smaller organism called the commensal benefits from the
association, but the host is neither benefited or harmed.
3. Parasitism - the parasite, the smaller of the two organisms, benefits and harms the host
or in some sense lives at the expense of the host. The host is damaged to a certain
degree because of the activities of the parasite.
4. Phoresis - The smaller one, the phoront, is carried by the larger companion, the host.
This association is mechanical for the purpose of transport from one place to another.
LIFE CYCLE OF PARASITES
1. Portal of entry - where a parasite gains entry into a host.
2. Infective stage - the developmental form of the parasite that is capable of entering its
host and continuing its development within the host.
3. Habitat - predetermined site of development and maturation of the parasite in a host.
4. Portal of exit - the route by which the parasite escapes the host.
5. Diagnostic stage - the developmental form of the parasite which leaves the host.
6. Source of infection - host from which the parasite is immediately transmitted to the
host.
DEVELOPMENTAL STAGE OF PROTOZOANS
1. Trophozoites - the metabolically active feeding and motile form, which are delicate and
do not survive long outside the body.
Symbiosis - means living together in close association of two phylogenetically different
organisms, which are called the symbionts.
Symbiotic relationships can be characterized by specifying the nature of the interactions
between the symbionts.
1. Mutualism - Mutualism is a relationship in which the organisms both benefit from a
relationship with each other.
- The symbionts are called mutualists.
2. Commensalism - the smaller organism called the commensal benefits from the
association, but the host is neither benefited or harmed.
3. Parasitism - the parasite, the smaller of the two organisms, benefits and harms the host
or in some sense lives at the expense of the host. The host is damaged to a certain
degree because of the activities of the parasite.
4. Phoresis - The smaller one, the phoront, is carried by the larger companion, the host.
This association is mechanical for the purpose of transport from one place to another.
LIFE CYCLE OF PARASITES
1. Portal of entry - where a parasite gains entry into a host.
2. Infective stage - the developmental form of the parasite that is capable of entering its
host and continuing its development within the host.
3. Habitat - predetermined site of development and maturation of the parasite in a host.
4. Portal of exit - the route by which the parasite escapes the host.
5. Diagnostic stage - the developmental form of the parasite which leaves the host.
6. Source of infection - host from which the parasite is immediately transmitted to the
host.
DEVELOPMENTAL STAGE OF PROTOZOANS
1. Trophozoites - the metabolically active feeding and motile form, which are delicate and
do not survive long outside the body.
