Introduction to Parasitology

Parasitology

- science that deals with the study of living organism that depends on another organism for the purpose of procuring food and securing protection

Parasites

Organisms that obtain its food and shelter from another organism and derive all the benefits from the association

Host

Organism that provides physical protection and nourishment to the parasites

Final/ definitive host

Adult or sexual stage of parasite =infective

Intermediate host

Larval stage of parasite

1st Intermediate host

Harbors early larval stages of the parasites (ex. Snail)

Secondary intermediate host

Harbors the infective larval stage of the parasite (ex. Fish and vegetables)

Reservoir host

Harbors the same species as that of man. Ensures continuity of the Lc of the parasite and additional source of infection. (Rodents and pig)

Paratenic host

Harbors the parasite in an arrested state of development (ex. Fresh water prawn, crab)

Accidental host

Host that shelters an organism which does not usually parasitize that host

Incidental host

Host that shelter organism but is unable to transmit the organism

Also known as dead-end host

Incidental host

Parasitism

is a process where the parasite, obtains its energy or sustenance from its host while producing effects that range from no demonstrable to severe pathology and death. Can be permanent or temporary.

Three types Host-Parasite Relationship

Symbiosis, mutualism and commensalism

Endoparasitism

Feeding of a parasite INSIDE the host

Ectoparasitism

Feeding of a parasite OUTSIDE the host

FACTORS AFFECTING TRANSMISSION OF PARASITES

Source of infection, effective mode of transmission and portal of entry, presence of a susceptible host, successful entry of the infective stage of the parasite, environmental condition, socio-economic factors

SOURCE OF EXPOSURE TO INFECTION

Soil transmitted group, snail transmitted group, arthropod transmitted group,animal/food transmitted group, contact transmitted group, one’s self (auto-infection)

2 types of vector

Biological vector and mechanical/phoretic vector

Soil-transmitted Group

Requires further development in the soil before they become infective

Snail-transmitted group

Requires further development w/in the snail body before they become infective

Arthropod-transmitted group

Insects that act as vectors of parasitic disease such as mosquitoes, sandfly and Tsetse fly

Animal/Food- transmitted group

Requires further development in the flesh of some animals that man consumes

Contact-transmitted group

Person to person transmission

One’s self (auto-infection)

Infected person is his own source of re-exposure

2 types of auto-infection

Internal and external

Types of Parasitic Worms

Enterobius vermicularis and Strongyloides stercoralis

Portal of Entry and Mode of Transmission

Mouth, skin, genitals, nose/intranasal, and transplacental

Mouth

Ingestion of the infective stage and intimate oral contact/kissing

Skin

Active larval penetration and bite of arthropod vector

Clinical Incubation Period

The interval between exposure to the parasites and appearance of the earliest signs and symptoms = FALSE NEGATIVE RESULT

Biological Incubation or Prepatent Period

The development of the parasite in a particular host and demonstration of the stages of the parasites in the different specimens = SCREENING-CONFIRMATORY

Direct/HOMOGENIC

Those with definitive host and WITHOUT intermediate host. No IH, man-man

Indirect/HETEROGENIC

those with definitive host and ONE intermediate host. Need IH to complete LC.

Clinical diagnosis

Recognition of the characteristic signs and symptoms of the infection of disease

Laboratory diagnosis

Identification of the parasites in the different specimens

Factors to consider before treatment

Severity, duration and intensity of infection and the probability of reinfection, efficacy, availability, toxicity and acceptability of the treatment

Classification of Parasites according to its effect to the host

Pathogenic, non-pathogenic

Pathogenic

Cause injury by its mechanical, traumatic or toxic activities

Non-pathogenic

Derive benefits from the host without causing any considerable damage or harm

Classification of Parasites according to mode of living

Obligate, Facultative, incidental, temporary, permanent, spurious/coprozoic

Obligate

Takes up a permanent residence; completely dependent upon oits host for existence

Facultative

Capable of leading both free and parasitic existence under favorable and appropriate circumstances

Incidental

One that establishes itself in a host in which it does not ordinarily lives

Temporary

Free living during part of existence and seeks only its host intermittently to obtain nourishment

Permanent

Remains on or in the body from early life to maturity

Spurious/ Coprozoic

One which parasitizes other hosts and recovered in a living or dead state from human excreta; no further development and do not cause injury or damage

Classification of Parasite according to the number of host in its life cycle

Monoxenous and Heteroxenous

Monoxenous

Lives within a single host during its entire life cycle

Heteroxenous

Lives within more than one host during its entire life cycle

Classification of Parasites according to set of sex organs

Monoecious and Dioecious

Monoecious

Hermaphroditic; complete functional set of sex organs in one parasite

Dioecious

Male and female sexes are separate. COPULATE-SEX