Medical Parasitology

• Medical Parasitology- Concerned primarily with parasites of humans and their medical significance, as well as their importance in human communities
• Symbiosis - Living together unlike organisms.
• Parasitology- The area of biology concerned with the phenomenon of dependence of one living organism to another.
• FORMS OF SYMBIOSIS

  1. Commensalism: one species benefits without harming or benefiting the other
  2. 2. Mutualism: two organisms mutually benefit from each other
  3. 3. Parasitism: one organism (parasite) lives in or on another organism for its survival and usually at the expense of the host
• Endoparasite - Parasite living inside the body of a host - Infection – presence of endoparasite in a host
• Ectoparasite - Parasite living outside the body of a host - Infestation – presence of ectoparasite on a host
• Obligate Parasite - Parasites that need a host at some stage of their life cycle to complete their development and to propagate their species - Ex. Tapeworms
• Facultative Parasites - Parasites that may exist in a free-living state or may become parasitic when the need arises
• Accidental or Incidental Parasite - Parasite which establishes itself in a host where it does not ordinarily live
• Permanent Parasite - Parasite that remains on or in the body of the host for its entire life
• Temporary Parasite - Parasite that lives on the host only for a short period of time
• Spurious Parasite - A free-living organism that passes through the digestive tract without infecting the host
• Definitive or Final host - One which the parasite attains sexual maturity
• Intermediate host - Harbors the asexual or larval stage of the parasite
• Paratenic host - One in which the parasite does not develop further to later stage
• Reservoir host - Allows the parasite’s life cycle to continue and become additional sources of human infection
• Vector - Responsible for transmitting the parasite from one host to another
• Biologic Vector - Transmits the parasite only after the parasite has completed its development within the host
• Mechanical or Phoretic Vector - Only transports the parasite
• Carrier - Harbors a particular pathogen without manifesting symptoms
• Exposure - The process of inoculating an infective agent
• Infection - The establishment of the infective agent in the host
• Incubation Period (Clinical incubation period) - Period between infection and evidence of symptoms
• Pre-patent period (Biologic incubation period) - Period between infection or acquisition of the parasite and evidence or demonstration of infection
• Autoinfection - An infected individual becomes his own direct source of infection - Ex. Enterobiasis or pinworm infection
• Superinfection / Hyper infection - An already infected individual is further infected with the same species leasing to massive infection with the parasite
• Sources of Infection

  ➢ Contaminated soil

  ➢ Contaminated water

  ➢ Food – uncooked or raw

  ➢ Arthropods

  ➢ Other animals (wild or domesticated)

  ➢ Another person
• MODE OF TRANSMISSION

  1. Mouth - Most common entry of parasitic infection.
  2. Skin Penetration
  3. Congenital transmission
  4. Trans mammary Infection
  5. Inhalation or airborne eggs
  6. Sexual Intercourse
• LIFE CYCLE- Can be simple (1 host only) or complicated life cycle (2 or more) - Parasites only attain sexual maturity in their definitive host
• Wuchereria bancrofti - A nematode that causes Lymphatic Filariasis
• Intermediate host is mosquito while definitive host is human - The more complicated the life cycle of parasite, the less they were able to survive

  Wuchereria bancrofti
• Epidemiology- Study of patterns, distribution and occurrence of disease
• Incidence - number of new cases of infection appearing in a population in a given period of time.
• Prevalence - No. (expressed as %) of individuals in a population estimated to be infected with a particular parasite species at a given time
• Cumulative prevalence - The % of individuals in a population infected with at least one parasite
• Intensity of infection - Refers to burden of infection which is related to the number of worms per infected person
• Morbidity - Clinical consequences of infection or diseases that affect an individual’s wellbeing.
• Deworming - The use of anthelminthic drugs in an individual or a public health program
• Cure rate - The number of previously positive subjects found to be egg negative on examination after deworming
• Egg reduction rate (ERR) - Percentage fall in egg counts after deworming