Introduction to
PARASITOLOGY
Ansharimar C. Balagosa, RMT
Instructor (Parasitology 2021-22, 2nd Sem)
PARASITOLOGY
area if Biology concerned with the phenomenon of
dependence of one living organism on another
scientific discipline concerned with the study of the
biology of parasites and parasitic diseases
CLINICAL PARASITOLOGY
concerned primarily with the animal parasites of
human and their medical sigificance, as well as their
importance in human communities
study of important parasites which causes diseases
to humans (classification, symptoms, disease,
lifecycle, transmission, treatment)
Biological
Relationships
SYMBIOSIS
The living together of unlike organisms.
3 forms:
Commensalism
Mutualism
Parasitism
SYMBIOSIS
Two species live together &
one species benefits from the
The living together of unlike organisms. relationship without harming or
benefiting the other.
Example: Entamoeba coli
3 forms:
Commensalism
Mutualism
Parasitism
SYMBIOSIS
Two organisms mutually
benefit from each other.
The living together of unlike organisms. Example:
3 forms:
Commensalism
Mutualism
Parasitism
SYMBIOSIS
Relationship that is beneficial to
one (parasite) at the expense of
The living together of unlike organisms. the other (host).
Example: Entamoeba histolytica
3 forms:
Commensalism
Mutualism
Parasitism
Host-Parasite
Relationships
HOST
Any living organism from which a
parasite obtains nourishment and
protection
Kinds of Host
Definitive/ Final Host
Intermediate Host
Paratenic Host
Reservoir Host
HOST
Any living organism from which a
parasite obtains nourishment and
protection
Kinds of Host
Harbors the sexual or the adult
Definitive/ Final Host stage of the life cycle of a
Intermediate Host parasite.
Paratenic Host
Reservoir Host Example: Human
HOST
Any living organism from which a
parasite obtains nourishment and
protection
Kinds of Host
Harbors the asexual or the
Definitive/ Final Host larval stage of the larval stage
Intermediate Host of the parasite.
Paratenic Host
Reservoir Host Example: Snail
HOST
Any living organism from which a
parasite obtains nourishment and
protection
Kinds of Host - The parasite does not develop further to
Definitive/ Final Host laetr stages.
Intermediate Host - It remains alive and is able to infect
Paratenic Host another susceptible host.
Reservoir Host
Example: Wild boar
HOST
Any living organism from which a
parasite obtains nourishment and
protection
Kinds of Host - Allow the parasite’s life cycle to
Definitive/ Final Host continue and become additional
Intermediate Host sources of human infection.
Paratenic Host
Reservoir Host Example: Pig
PARASITES
Any organism that lives inside or on the
body surface of another organism (host)
which is usually larger organis m that
provides physical protection (shelter) and
nourishment (food) for survival.
PARASITES
ENDOPARASITES ECTOPARASITES
parasites that live inside the parasites that live outside the
host’s body host’s body
Infection Infestation
A parasite is considered ERRATIC when its found in an
organ that is not its usual habitat.
PARASITES
OBLIGATE PARASITES FACULTATIVE PARASITES
They need a host at some stage It may exist in a free-living state
of their life cycle to complete or may become parasitic when
their development and to the need arises.
propagate their species.
PARASITES
TEMPORARY PARASITES PERMANENT PARASITES
It lives on the host only for a It remains in the body of the
short period of time. host for its entire life.
PARASITES
ACCIDENTAL/INCIDENTAL SPURIOUS PARASITES
PARASITES
A free-living organism that
It establishes itself in a host passes through the digestive
where it does not ordinarily live. tract without infecting the host.
VECTORS
Responsible for transmitting the
parasite from one host to another.
VECTORS
Biologic Vector
- It transmits the parasite only after the
parasite has completed its development
within the host.
- Essential part in the life cycle of the
parasite.
Example: Aedes mosquito- Lymphatic
filariasis
VECTORS
Mechanical Vector
- Only transport the parasite
Example: Flies and Cockroaches
EXPOSURE and
INFECTION
Exposure and Infection
EXPOSURE INFECTION
It is the process of inoculating It connotes the establishment of
an infective agent. the infective agent in the host.
CARRIER
It harbors a particular pathogen
without manifesting any signs
and symptoms.
Incubation & Pre-Patent Period
PRE-PATENT Period
INCUBATION Period
• The period between infection
• The period between infection
or acquisition of the parasite
and evidence of symptoms.
a n d e v i d e n c e o r
• a.k.a Clinical Incubation
demonstration of infection.
Period
• a.k.a Biologic Incubation
Period
AUTOINFECTION
It results when an infected
individual becomes his own
direct source of infection.
Example: Enterobiasis
SOURCES of
INFECTION
• Water
• Food
• Contaminated Soil and Water
• Consumption of undercooked
– MOST COMMON
or raw freshwater fish
• Lack of sanitary toilets
• Raw crabs
• Use of night soil or human
• Arthropods
excreta as fertilizer
• Cats
• Rats
MODES of
TRANSMISSION
Contaminated Food & Water
Foodborne
• Cestodes
• Trematodes
• Intestinal Protozoans
Drinking Contaminated Water
• Entamoeba histolytica
• Giardia lamblia
Portal of Entry
Ingesting raw or improperly cooked freshwater fish
• Clonorchis
• Opistorchis
• Haplorchis
Skin Penetration
Skin Exposure to Soil
• Hookworms
• Strongyloides
Enter skin via water
Portal of Entry
• Schistosoma
ARTHROPODS
• Malaria
• Filariasis
• Leishmaniasis
• Tryponasomiasis
Portal of Entry • Babesiosis
Congenital Transmission
• Toxoplasma gondii
• Ancylostoma
• Strongyloides
Inhalation of Airborne Eggs
• Enterobius
SEXUAL INTERCOURSE
• Trichomonas vaginalis
LIFE CYCLE
• The larval stage of the
• Most parasitic organisms attain parasite may pass through
sexual maturity in their definitive different stages in an
hosts. intermediate host before it
• Some spend entire lives within a
reaches a final host.
host with one generation after
another. • As the life cycle becomes
• Some are exposed to the external more complicated, the
environment before being taken up lesser the chances are for
by an appropriate host. the individual parasite to
survive.
EPIDEMIOLOGIC
MEASURES
EPIDEMIOLOGY
The study of patterns,
distribution, and occurrence of
disease.
INCIDENCE
The number of new cases of
infection appearing in a
population in a given period of
time.
PREVALENCE
• The number of individuals in a
population estimated to be
infected with a particular
parasite species at a given
time.
• Usually expressed as
percentage
Cummulative Prevalence
The percentage of individuals in
a population infected with at
least one parasite.
Intensity of Infection
• It refers to burden of infection that is related to the number
of worms per infected person.
• a.k.a Worm burden
• It can be measured directly or indirectly
• Directly = Counting expelled worms during treatment
• Indirectly = Counting helminth eggs excreted in the feces
(# of eggs / gram)
MORBIDITY
Clinical consequences of
infections or diseases that affect
an individual’s well being.
TREATMENT
DEWORMING
The use of anthelminthic drugs
in an individual or a public
health program.
CURE RATE
• It refers to the number of previously positive subjects
found to be egg negative on examination of stool or
urine sample using a standard procedure at a set
time after deworming.
• Usually expressed as percentage.
Egg Reduction Rate
It is the percentage fall in egg counts after deworming
based on examination of a stool or urine sample using
a standard procedure at a set time after a treatment.
SELECTIVE TARGETED UNIVERSAL
Treatment Treatment Treatment
It involves individual-level It is a group-level It is a population-level
deworming with selection deworming where the deworming in which the
for treatment based on a group to be treated may be community is treated
diagnosis of infection or an defined by age, sex, or irrespective of age, sex,
assessment of the intensity other social characteristics infection status, or other
of infection, or based on irrespective of infection social characteristics.
presumptive grounds. status.
Preventive Chemotherapy
It is the regular, systematic, large-scale intervention
involving the administration of one or more drugs to
selected population groups with the aim of reducing
morbidity and transmission of selected helminth
infections.
COVERAGE
• It refers to the proportion of the target population
reached by an intervention.
• It could be the percentage of school-age children
treated during a treatment day.
EFFECTIVENESS
EFFICACY • It is a measure of the effect of a drug
against an infective agent in a
It is the effect of a drug against particular host, living in a particular
environment with specific ecological,
an infective agent in ideal
immunological, and epidemiological
experimental conditions and determinants.
isolated from any context. • Qualitative and Quantitative
diagnostic tests
• Cure Rate & Egg Reduction Rate
DRUG RESISTANCE
It is a genetically transmitted loss of susceptibility to a
drug in a parasite population that was previously
sensitive to the appropriate therapeutic dose.
PREVENTION and
CONTROL
Morbidity Control
• It is the avoidance of illness caused by infections.
• It may be achieved by periodically deworming
individuals or groups, known to be at risk of
morbidity.
Information-Education-Communication
It is a health education strategy that aims to
encourage people to adapt and maintain healthy
life practices.
ENVIRONMENTAL Sanitation SANITATION
• It involves interventions to reduce • It is the provision of access to
environmental health risks. adequate facilities for the safe
• It also involves the control of disposal of human excreta.
vectors, intermediate hosts, and • It is usually combined with
reservoirs of disease. access to safe drinking water.
Disease ERADICATION Disease ELIMINATION
Permanent reduction to zero of • It is a reduction to zero of the
the worldwide incidence of incidence of a specified disease
in a defined geographic area as a
infection caused by a specific
result of deliberate efforts.
agent, as a result of deliberate • Continued interventions /
efforts. surveillance
Introduction to
PARASITOLOGY
Ansharimar C. Balagosa, RMT
Instructor (Parasitology 2021-22, 2nd Sem)
