Parasitology LC1

• Parasitic diseases have caused serious health problems in the country and worldwide
• Parasitology is the study of animal parasites
• Medical Parasitology is concerned with animal parasites of humans and their medical significance
• Tropical Medicine deals with tropical diseases and medical problems of tropical regions
• Tropical diseases are indigenous to or endemic in tropical areas but can also be sporadic or epidemic in non-tropical areas
• Malaria is a significant parasitic disease that kills approximately half a billion people per year
• Biologic Relationships:

  • Symbiosis: living together of unlike organisms for mutual benefit
  • Commensalism: two species live together with one benefiting without harming the other
  • Mutualism: two organisms mutually benefit from each other
  • Parasitism: one organism lives on another for survival at the expense of the host
• Parasite:

  • An organism living on or in the host for protection and nourishment
  • Endoparasite lives inside the host's body causing infection
  • Ectoparasite lives outside or on the host's body causing infestation
  • Erratic found in an organ not its usual habitat
  • Obligate Parasites need a host for development and reproduction
  • Facultative Parasites may become parasitic when needed
• According to Host Specificity:

  • Accidental/Incidental: establishes in a host where it does not usually live
  • Permanent: remains in the host's body for its entire life
  • Temporary: lives in the host for a short period
  • Spurious/Coprozoic: passes through the digestive tract without infecting the host
• Host:

  • Any organism harboring the parasite
  • Classified as Definitive/Final, Intermediate, Paratenic, Reservoir Hosts
  • Definitive host is where the parasite attains sexual maturity
  • Intermediate host harbors the larval stage of the parasite
  • Paratenic host does not allow parasite development further
  • Reservoir hosts allow the parasite's life cycle to continue
• Vectors:

  • Responsible for transmitting the parasite from one host to another
  • Biologic Vector transmits the parasite after completing its development
  • Mechanical/Phoretic only transport the parasite
• Exposure and Infection:

  • Pathogens are harmful parasites causing disease
  • Carrier harbors a pathogen without showing symptoms
  • Exposure is the process of inoculating an infecting agent
  • Infection is the establishment of a parasite in the host
  • Infestation is the presence of an ectoparasite on the host
• Incubation Period:

  • Clinical Incubation Period is between infection and symptom evidence
  • Biologic Incubation Period is between infection and demonstration of infection
  • Autoinfection occurs when an infected individual becomes its own source of infection
  • Superinfection/Hyperinfection is when already infected individuals are further infected
• Autoinfection can lead to superinfection or hyperinfection
• Superinfection/Hyperinfection:

  • Already infected individuals are further infected with the same species leading to massive infection with the parasite
• Sources of autoinfection:

  • Another person, his beddings and clothing, immediate environment he has contaminated
  • One’s self (Autoinfection)
  • Parasites like Enterobius vermicularis, Strongyloides stercoralis, Capillaria philippinensis, Hymenolepis nana
• Sources of infection in parasitology:

  • Mouth serves as the common portal of entry
  • Contaminated soil and water are the primary sources of infection when entry occurs through the mouth
  • Contaminated soil and water:
  • Hygiene in third world countries often parallels poverty
  • Lack of sanitary toilets and use of night soil or human excreta as fertilizer allow eggs to get in contact with the soil
  • Water may be contaminated with cysts of amebae or flagellates and cercariae of Schistosoma, especially during rainy seasons
• • Soil-Transmitted Helminths (STH) include hookworms, Ascaris lumbricoides, Trichuris trichiura, Strongyloides stercoralis
• Modes of transmission:

  • Mouth is the most common route of transmission for parasites like Taenia solium, Taenia saginata, Diphyllobothrium latum
  • Skin penetration: Hookworms and Strongyloides enter via exposure of skin to soil, Schistosoma species enter the skin via water
  • Bites from arthropods transmit parasites like malaria, filariasis, leishmaniasis, trypanosomiasis
  • Congenital transmission: Toxoplasma gondii trophozoites can cross the placental barrier during pregnancy
  • Inhalation of air-borne eggs: Enterobius vermicularis
  • Sexual intercourse: Trichomonas vaginalis
• Nomenclature:

  • Classified according to the International Code of Zoological Nomenclature
  • Scientific names are Latinized; family names are formed by adding -idae to the stem of the genus type; generic names consist of a single word written in initial capital letter; specific names always begin with a small letter
  • Genera and species names are italicized or underlined when written
  • Example: Ascaris lumbricoides
• Life cycle:

  • Simple life cycle: Ova → Larva → Adult
  • Complicated life cycle involves 2 or more hosts, with some parasites attaining sexual maturity in definitive hosts and others having developmental forms in intermediate hosts and human hosts
  • Example: Schistosoma spp.
• Epidemiologic measures:

  • Epidemiology studies patterns, distribution, and occurrence of disease
  • Incidence: Number of new cases of infection appearing in a population in a given period of time
  • Prevalence: Percentage of individuals in a population estimated to be infected with a particular parasite species at a given time
  • Cumulative Prevalence: Percentage of individuals infected with at least one parasite
  • Intensity of infection: Burden related to the number of worms per infected person
  • Morbidity: Clinical consequences of infections or diseases affecting well-being
• • Preventive chemotherapy: Large-scale intervention to reduce morbidity and transmission of helminth infections
  • Efficacy: Effect of drug against an infective agent in ideal conditions
  • Effectiveness: Measure of the effect of a drug in a particular host and environment
  • Drug resistance: Genetically transmitted loss of susceptibility to a drug in a parasite population
• Treatment:

  • Deworming involves the use of anti-helminthic drugs in individuals or public health programs
  • Cure rate: Percentage of previously positive subjects found to be egg negative after deworming
  • Egg Reduction Rate (ERR): Percentage fall in egg counts after deworming
  • Selective treatment: Individual-level deworming based on diagnosis or intensity of infection
  • Targeted treatment: Group-level deworming based on defined risk groups
  • Universal treatment: Population-level deworming irrespective of age, sex, or infection status
• Drug Resistance:

  • Genetically transmitted loss of susceptibility to a drug in a parasite population that was previously sensitive to the appropriate therapeutic dose
  • The parasite developed a new defense against a certain drug which loses the drug's susceptibility
• Prevention and Control strategies:

  • Different strategies used to prevent the infection/infestation of parasites
  • Morbidity Control: Avoidance of illness caused by infections
  • Information-Education-Communication (IEC): Health education strategy to encourage healthy life practices
  • Environmental Management: Planning, organization, and monitoring of activities to prevent or minimize vector or intermediate host propagation and reduce contact between humans and the infective agent
  • Government leaders are responsible for prioritizing health and environment in environmental management
• • Environmental Sanitation: Interventions to reduce environmental health risks including safe disposal of waste and control of vectors
  • Sanitation: Provision of access to safe disposal of human excreta and safe drinking water
• Eradication vs Elimination:

  • Disease Eradication: Permanent reduction to zero of the worldwide incidence of infection caused by a specific agent
  • Disease Elimination: Reduction to zero of the incidence of a specified disease in a defined geographic area
• • Arthropoda (Insects, Spiders, Mites, Ticks): Segmented animals with a chitinous covering, well-developed digestive system, and separate sexes with classes like Crustacea, Chilopoda, Arachnida, and Insecta
• Important Groups of Animal Parasites:

  • Protozoa: single-celled organisms with different subclasses like Sarcomastigophora, Sarcodina, Ciliophora, Apicomplexa, and Microsporidia
  • Platyhelminthes (Flatworms): Multicellular animals with classes Turbellaria, Trematoda (Flukes), and Cestoda (Tapeworms)
  • Nematoda (Roundworms): Elongate, cylindrical worms with separate sexes and a well-developed digestive tract
  • Acanthocephala (Thorny-headed Worms): Thorny-headed worms that are endoparasitic with separate sexes