Introduction to Parasitology

Module Overview

• Module 5 provides an introduction to parasitology.
• The module will cover kinds of parasites, vectors, and hosts.
• The module will cover the phases of parasitism.

Outline for Module 1

• Module objectives serve as a starting point.
• The historical development of parasitology will be explored.
• Key terms will be defined.
• Parasites, vectors, and hosts will be classified.
• Phases of Parasitism will be understood.
• Incubation Period will be studied.
• Immunity will be defined.
• Epidemiology will be covered.
• Focus on Diagnosis, Treatment, Prevention and Control of Parasitoses will be highlighted.

Misconceptions

• Parasites were once believed to be beneficial to humans in the 17th and 18th centuries.
• Lice were thought to protect children from disease.
• Leeches were used to draw blood as a cure.
• Intestinal parasites were believed to aid in cleaning the digestive tract.
• Powdered Ascaris was thought to treat impotency in Chinese medicine.
• Heads of tapeworms (scolices) were used for weight control in France.

Parasite Definition

• A parasite is a living organism that relies on another organism for food and shelter.
• In Greek, "para" means near, and "sites" means food.

Parasitism Definition

• Parasitism is a type of symbiosis where one species (parasite) lives on or in another (host).
• The parasite benefits by obtaining nourishment, shelter, or protection from the host.
• The physical smaller organism, the parasite, gains benefits while the host is harmed.
• Parasitic relationships can be temporary, facultative, or obligatory.
• The relationship tends to be intimate, and usually obligatory for it to work.
• Parasites need specialized mechanisms to overcome host defenses in order to thrive.
• Parasites are often species-specific.

Harm Caused by Parasites

• Parasites can deprive the host of digested food.
• Parasites can cause blockages of food, blood, lymph, or bile passages.
• Parasites can cause tissue damage through rupture, enzymatic digestion, autolysis, or toxin secretion.

Kinds of Parasites

• Macroparasites are multicellular, visible to the naked eye, including helminth parasites like flukes, tapeworms, and roundworms.
• Microparasites are small, generally unicellular, and invisible to the naked eye, including protozoan parasites.
• Ectoparasites live on the surface of the host, such as ticks, lice, leeches, mites, and fleas.
• Some aquatic leeches locate hosts by sensing movement and confirm identity through skin temperature and chemical cues.
• Endoparasites live within the host, like roundworms and tapeworms in the gut.
• Obligatory parasites depend entirely on the host for their existence and cannot survive without it.
• Facultative parasites can choose between a free-living or parasitic existence.
• Spurious parasites pass through the human body without development or causing injury.
• Examples of intermediate parasites include leeches, bed bugs, and parasites that visit their hosts for short periods.
• Parasites can be either pathogenic(causing disease) or non-pathogenic(not causing disease).

According to Where Parasites Are Found

• Coprophilic parasites are protozoan organisms that live and multiply in moist fecal matter outside the body.
• Hematozoic parasites live inside a red blood cell, e.g., Plasmodium.
• Cytozoic parasites live inside the cell or tissue, e.g., Plasmodium, Isospora hominis.
• Coelozoic parasites live in body cavities, e.g., Acanthocheilonema perstans.
• Enterozoic parasites live inside the lumen of the intestines, e.g., Ascaris lumbricoides.

Other Terms

• Hyperparasites are parasites within a parasite, like malaria in mosquitoes or tapeworm larvae in fleas (hyperparasitoidism).
• Pseudoparasites are objects mistaken for parasites.
• Wandering or aberrant parasites can't transmit from man to man, but develops abnormally in a person from migrating to the brain instead of intestines.

Hosts

• Monoxenous parasites have only one host.
• Heteroxenous parasites have two or more hosts from widely separated taxonomic groups.
• Dioecious organisms have separate sexes.
• Monoecious organisms have both reproductive organs in the same individual.

Host Definitions

• The definitive or final host is where the parasite reaches sexual maturity and reproduces.
• The intermediate or secondary host provides some development but does not reach sexual maturity.
• The paratenic host is an intermediate host in which the parasite doesn't develop, but is essential for the parasite.
• The reservoir host are non-human animals that serve as sources of infection to humans and can harbor a pathogen indefinitely with no ill effects.

Vectors

• Vectors transmit parasites from host to host.
• Biological vectors are essential for the parasite's life cycle.
• Mechanical vectors are inessential for the parasite's cycle; example of cyst transport by the legs of vectors.
• Anthropophilic vectors prefer human blood when it is available.
• Zoophilic vectors prefer animal blood when it is available.
• Zoonosis is described as diseases of animals that are transmittable to humans.

Phases of Parasitism

• Contact & Entry to the Host from contaminated soil, contaminated water, food containing the immature infective stage of the parasite.
• Skin penetration can cause bites from arthropod vector and due to direct penetration of infective forms.
• From a domestic or wild animal harboring the parasite.
• From another person, his clothing, bedding, or immediate environment which he has contaminated to another
• Airborne and blood transmission can transmit these diseases
• Transplacental (i.e. congenital)
• Autoinfection
• After the entry, Migration of parasite in the host to its habitat occurs
• Maturation and Reproduction involve the parasite's use of the host's nutrients for growth, energy and multiplication.

Incubation Period

• Biological Incubation Period relates to the development of the parasite.
• Starts with the entry of the parasite to its host & ends demonstrates with detection in feces test.
• Clinical Incubation Period is interval between exposure & earliest evidence of symptoms.
• Infection: entry & multiplication of pathogen in the body.
• Infestation: lodgment, development & reproduction of arthropods on the body.

Immunity

• In animal parisitoses is rarely solid, with notable exceptions as natural parasitic infections that appear to confer immunity to subsequent attack.
• Parasites adapted to live in a host can thrive better there.

The Environment

• The presence or absence of a number of biological, chemical & physical factors in the environment affects its densities & distribution.
• Flora-vegetation serves as food, shelter influences parasite population.
• Fauna- animal population constitutes potential hosts and maintains parasites.
• Water- infective forms of parasites require water to migrate & reach a host.
• Host population density and behavior - densities of transport, intermediate & definitive hosts affect parasite population densities.
• Climate, temperature, and humidity are important to parasites.

Diagnosis, Treatment, Prevention and Control of Parisitoses

• Diagnosis has Clinical and Laboratory/diagnostic methods of approach.
• Epidemiology deals with the incidence, distribution, and possible control of diseases and other factors relating to health.
• Epidemiologic studies provide info on the prevalence of parasites in a population
• Epidemiologic studies indicate whether infections are endemic, hyperendemic, epidemic & sporadic.
• Epidemiologic studies provide clues as to the sources of exposure.
• Epidemiologic studies direct attention to the amount of illness in the community.
• Prevalence rate is the frequency of occurrence of a disease in a population in a time frame.
• Prevalence rates includes old and new cases and is usually expressed in %.
• Incidence rate is the frequency of occurrence of a disease in a population in a time frame.
• Incidence rate includes only new cases (%).
• Mortality rate expresses the frequency of deaths among those having the disease in a community and is expressed in deaths per 100,000 per year.
• Morbidity rate expresses the frequency of being sick of the disease; & is commonly reported as cases of notifiable disease per 1,000 per year.
• Endemicity is when a disease in the human population maintains a relatively steady, moderate level.
• Hyperendemic means if prevalence is high.
• Epidemic- a sharp rise in the incidence or an outbreak of considerable intensity occurs
• Sporadic- only occasionally in one or at most a few members of the community.
• Endemicity- commonly associated with a certain degree of tolerance to the pathogen.
• Epidemicity- typically results from introduction of a new agent into a community which has a sudden development of an enhanced pathogenicity of the infectious agent, or a vector.
• Accurate specific diagnosis must be considered before treatment, severity, duration & intensity of infection & the probability of reinfection.
• Efficacy, availability, toxicology, & acceptability affects treatment.
• Control of a parasitic disease means its restraint through symptomatic relief or repression but not elimination of the causative agent; the reduction of furthering an epidemic.
• Prerequisites: A prerequisite to control and is a clear understanding of the epidemiology of every causative organization.
• Characteristics of the parasite.
• Conditions surrounding the parasite's survival
• Control the source of the agent for preventing exposure.
• Physicians must detect, accurately diagnose & evacuate the disease.
• Treatment of the patient; search for other cases.
• Doctors must determine the source of the infection.
• Provide patients with support; and educate.
• Doctors are to help with community measures.
• The control and prevention of the parasitoses is directed to everyone.
• Methods are designed to cut a link in the parasitic cycle.
• Measures directed to the parasite from prompt examination; to synthetic and chemical applications to eradicate vector.
• Measures direct chemical applications to arthropod, bodies of water, through control thru waster.

Parasite's Goal

• Survival, not to be detected or eradicated,
• Some of the intelligent things organisms must do for human survival by finding other ways due to human intervention.
• These organisms survival could complicate human lives.