Mls108

• Parasitology is the area of biology concerned with the dependence of one living organism on another
• Medical Parasitology focuses on parasites of humans and their medical significance
• Tropical Medicine deals with tropical diseases and special medical problems of tropical regions
• Symbiosis is the living together of unlike organisms
• Types of Symbiotic Associations:

  • Phoresis: one organism is mechanically carried on or in another species for a limited time period
  • Commensalism: two species live together, one benefits without harming the other
  • Mutualism: two organisms mutually benefit from each other
  • Parasitism: one organism lives in or on another, depending on the latter for survival
• Classification of Parasites:

  • Ectoparasite: lives outside the host's body
  • Endoparasite: lives inside the host's body
  • Obligate Parasite: needs a host to complete its life cycle
  • Facultative Parasite: may become parasitic when needed
  • Accidental or incidental: infects a host where it does not usually live
  • Permanent Parasite: remains on or in the host for its entire life
  • Temporary Parasite: lives on the host for a short period
  • Spurious Parasite: passes through the digestive tract without infecting the host
• Classification of Parasites:

  • Protozoa
  • Helminths:
  • Nematodes (roundworms)
  • Trematodes (tapeworms)
  • Cestodes (flatworms)
  • Ectoparasites:
  • Arthropods
• Host:

  • Organism that harbors the parasite
  • Definitive or Final Host: harbors the sexual or adult stage of parasite
  • Intermediate Host: harbors the asexual or larval stage of the parasite
  • Paratenic Host: parasite does not develop further but remains alive
  • Reservoir Host: animals harboring the same parasite species as humans
  • Vectors: transmit parasites from one host to another
• Exposure and Infection:

  • Carrier: harbors a pathogen without showing symptoms
  • Exposure: process of inoculating an infective agent
  • Infection: establishment of the infective agent in the host
  • Incubation Period: time between infection and symptom appearance
  • Pre-patent Period: time between infection and demonstration of infection
  • Autoinfection: infected individual becomes their own source of infection
  • Superinfection: further infection with the same species leading to massive infection
• Sources of Infection:

  • Contaminated soil, water, food, arthropods, animals, beddings, clothing, and humans
  • Modes of Transmission:
  • Mouth (Ingestion)
  • Skin penetration
  • Vector bites
  • Congenital transmission
  • Transmammary transmission
  • Inhalation
  • Sexual intercourse
• Nomenclature and Classification:

  • Animal parasites classified according to the International Code of Zoological Nomenclature
  • Scientific names of parasites are latinized and italicized or underlined
  • Consist of genus and species components
  • Epidemiologic Measures:
  • Epidemiology: study of disease patterns, distribution, and occurrence
  • Incidence: new cases of infection in a population
  • Prevalence: percentage of individuals infected with a parasite species
  • Intensity of Infection: burden of infection related to the number of worms per infected person
• • Effectiveness: measure of a drug's effect in a specific environment
• Treatment:

  • Deworming: use of antihelminthic drugs in individuals or public health programs
  • Cure rate: percentage of previously positive subjects found negative after deworming
  • Egg Reduction Rate (ERR): percentage fall in egg counts after treatment
  • Selective, Targeted, and Universal Treatment: different approaches to deworming
  • Coverage: proportion of the target population reached by an intervention
  • Drug-resistance: genetically transmitted loss of susceptibility to a drug in worm population
  • Efficacy: effect of a drug against an infective agent in ideal conditions
• Prevention and Control:

  • Morbidity control, information-education-communication, environmental management, sanitation
  • Eradication vs. Elimination:
  • Disease eradication: permanent reduction to zero of worldwide incidence of a specific agent
  • Disease elimination: reduction to zero of a specified disease in a defined geographic area
  • Host-Immune Response:
  • Innate and Acquired Immune Responses
  • Innate Response: non-specific mechanisms to eliminate pathogens
  • Acquired Immune Response: specific response to parasitic antigens
• If infected by the virus and not taking antiretroviral drugs, CD4 T-helper lymphocytes significantly decrease in number in the blood
• Decrease in CD4 T-helper lymphocytes increases the risk of being infected with many other diseases and parasitic infections
• Protozoan parasites can infect CD4 T-helper lymphocytes
• Protozoa are one-celled organisms with a nucleus, cytoplasm, outer membrane, and organelles
• Protozoa are eukaryotic cells with organized cell organelles and functions
• Protozoa move using their locomotory apparatus, such as cilia or flagella
• Balantidium coli is a ciliated protozoa of medical importance, commonly found in swine and can infect humans
• Protozoa use pseudopodia, cilia, or flagella for movement
• Protozoa require a wet environment for feeding, locomotion, osmoregulation, and reproduction
• In stool examination, diarrheic or watery stool contains the trophozoite stage of amoebic parasites
• Protozoan parasites have two stages: cyst (infective) and trophozoite (vegetative)
• Infections associated with amoebas are related to the oral route through ingestion of mature cysts
• Entamoeba histolytica is the only pathogenic species among intestinal amoebae
• Entamoeba histolytica can cause colitis and liver abscess
• Protozoans belong to the Kingdom Protista
• Classification of protozoan parasites includes Sarcomastigophora, Ciliophora, Apicomplexa, and Microspora
• Sarcomastigophora includes Sarcodina (amebas) and Mastigophora (flagellates)
• Ciliophora includes ciliates
• Apicomplexa have an apical complex at the anterior end
• Microspora consists of spore-forming parasites
• Intestinal amoebae include Entamoeba histolytica, Entamoeba dispar, Entamoeba coli, and others
• Protozoa found in stool specimens of humans include amoebae
• Trophozoites of Entamoeba histolytica have pseudopods and can invade tissues
• Entamoeba histolytica cysts contain 4 nuclei
• Entamoeba histolytica causes amebic dysentery, amebic colitis, and liver abscesses
• Mode of transmission of Entamoeba histolytica includes ingestion of mature cysts and direct colonic inoculation