Intro

• PARASITES AND PARASITISM


  Living organisms associated with food for all or part of their life-cycle, the organism providing the food is generally called the host
• Parasitology


  Area of biology concerned with the phenomenon of dependence of one living organism on another
• Parasites' adaptation

  Ensuring distribution and making contact with a new host
• Parasites' survival


  Equipped to survive within a certain habitat
• Parasites


  Organisms dependent on another organism for food and shelter
• Disturbance of equilibrium


  Could lead to pathological effects on the host or destruction of the parasite
• Clinical Parasitology


  Concerned with animal parasites in humans and their medical significance, as well as their importance in human communities
• Presence of the parasite


  Stimulates the host to try and destroy the parasite
• How to study the parasite

  First, the biology of the parasite; second, the biology of the host (the parasite’s environment)
• Parasitology investigates the biology of the parasite, variations in life-cycle, methods of invasion of the host, migration and maturation within the host, the effect of the parasite upon the host, host reaction and response to the parasite, methods of escape from the host, distribution of the parasite
• Types of vectors

  • Biological vectors: important in parasites life cycle, transmit the parasite only after completed its development within the host
  • Mechanical/Phoretic vector: transports the parasite
• Disease/Infection

  • Infection: entry, development, establishment, and multiplication of parasite in the host
  • Auto-infection: infected individual becomes his/her own direct source of infection
  • Super-infection/Hyper-infection: infected individual is re-infected with the same
  • Endemic: infection always existing in a place or region
  • Epidemic: spread of infection to a large population
  • Pandemic: widespread epidemic involving worldwide population
  • Incubation period: period between acquisition of parasite or entry and manifestation of infection
• Sources of Infection

  • Contaminated soil and water
  • Food (contaminated with the infective stage of parasite)
  • Arthropod vectors
  • Domestic or wild animals
  • Another person (Infected individuals)
  • Own self (auto-infection)
• Parasitic Infection has a greater impact in developing countries compared to developed countries due to various factors
• Mode of Transmission

  • Ingestion (contaminated food and water)
  • Inhalation
  • Skin penetration
  • Arthropods (bites)
  • Congenital transmission
  • Trans-mammary
  • Sexual Intercourse (STD)
• Types of hosts

  • Definitive host (harbors the sexual stage or adult)
  • Intermediate host (harbors the asexual stage)
  • Reservoir host (harbors the parasite other than the host)
  • Carriers (harbors the parasite but do not manifest the disease/infection)
  • Paratenic host (harbors the arrested stage of parasite but still alive and capable of infecting susceptible hosts)
• Biological relationships

  • Symbiosis: permanent association of two organisms that cannot exist independently, mutually beneficial relationship
• Parasite life cycle

  Enters the host as an egg or infectious larva, grows, develops, matures, reproduces, deposits eggs or larvae, which escape to invade another host
• Genetic make-up of the host


  May influence the interaction between the host and the parasite
• Frequently encountered methods of invasion

  • Oral
  • Penetration by specialized larvae
  • Contact
  • Via a vector
• Methods of Invasion and Escape

  1. Parasites must have means of locating and invading new hosts

  2. Next generation must be able to escape from the host
• Effect of Parasites to the Hosts

  • Interference with vital processes of the host through the enzyme system
  • Invasion and destruction of host tissues
  • Deprivation of essential nutrients
  • Inflammatory reaction to parasite
• Factors affecting the prevalence of parasites

  • Host
  • Agents
  • Environmental factors (weather, topography, geographical location, etc.)
• Nutritional status of the host

  • CHON diet not suitable for protozoan development
  • CHO diet favors the development of tapeworm
• Resistance and Immunity

  • Human host has weak immune response to parasites
  • Cellular Immune response
  • Humoral Immune response
• Methods of escape

  • Escape via feces or urine
  • Via a vector
  • Parasite may actively break through the skin to escape
• Diagnosis of parasitic disease

  1. Based on symptomatology and clinical manifestation

  2. Proper identification of parasite species through laboratory examination of appropriate sample
• Treatment of parasitic disease

  1. Specific chemotherapy

  2. Medical and surgical measures

  3. Attention to the nutritional status
• Examples of Platyhelminthes (flatworms)

  • Class Cestoda (tapeworms):
  • Class Trematoda (flukes):
• Humoral Immune response


  1. cells recognize molecules of parasites through the immunoglobulin receptors leading to cell differentiation and production of antibodies
• Damage of the parasite can occur through

  • Direct neutralization
  • Complement fixation
• Other barriers that prevent infection

  • Physiochemical barriers: intact skin, chemical substances produced by the host
  • Innate or Natural resistance: e.g. Resistance to malaria by black people
  • Specific Immunity: acquired from previous infection
• General Preventive Measures

  • Reduction of the source of infection by therapeutic measures
  • Health education to prevent dissemination of infection and to reduce the opportunities of infection
  • Sanitary control in water, food, living and working conditions and proper waste disposal
  • Control of reservoir hosts and vectors
  • Construction of biological barriers to the transmission of parasites (based on biological and epidemiological knowledge)
• Recognition of the parasite by macrophages

  Macrophages could either devour the entire parasite or ingest molecules released by the parasites which triggers the production of T-lymphocytes
• Parasite is derived from the Greek word para which mean beside and sitos, food
• Parasitology investigates:

  • the biology of the parasite,
  • variations in life-cycle,
  • methods of invasion of the host,
  • migration and maturation within the host,
  • the effect of the parasite upon the host,
  • host reaction and response to the parasite,
  • methods of escape from the host,
  • distribution of the parasite
• Type of parasite (in terms of mode of development)

  • Coprozoic parasites
  • Hematozoic:
  • Cytozoic:
  • Coelozoic:
  • Enterozoic:
  • Intermittent parasite:
  • Erratic parasite:
  • Erratic parasite:
  • Pseudo-parasites
  • Obligate parasites
  • Facultative Parasites
  • Incidental Parasite
  • Permanent Parasites
  • Temporary Parasites
  • Non/Pathogenic
  • Opportunist
• Endoparasites

  living inside the body of the host

  presence of parasite is termed as Infection
• Ectoparasites

  living outside the host

  presence of parasites is termed as Infestation
• Obligate parasite -cannot survive without a host

  -needs host for their development