GENERAL CONSIDERATIONS Parasitology area of biology concerned with

GENERAL CONSIDERATIONS Parasitology - area of biology concerned with phenomenon of dependence of one living organism on another Medical Parasitology - concerned primarily with the animal parasites of humans, their medical significance as well as their importance in human communities.

TROPICAL MEDICINE: Tropical disease: an illness indigenous to or endemic in a tropical area. - sporadic ) in non - tropical - epidemic ) A. BIOLOGICAL RELATIONSHIP Symbiosis living together of unlike organisms a. Commensalism E. coli in intestinal lumen

b. Mutualism termites and flagellates in their digestive system c. Parasitism Entamoeba histolytica in intestinal lumen

B. PARASITE 1. Relationship as to location or habitat - endoparasite - ectoparasite * infestation infection erratic - obligate parasites - need a host to develop and propagate their species (tapeworms) - facultative parasite - may exist in a free living stage or may become parasitic when the need arises

2. Host specificity a. incidental parasite - establishes itself in a host where it does not ordinarily live b. permanent parasite - remains on or in the host for its entire life c. temporary - lives on the host for a short period of time d. spurious - a free living organism that passes through the digestive tract without infecting the host

C. HOST Types: 1. Definitive or final host - one in which parasite attains sexual maturity (taenias) in man 2. Intermediate host - harbors the asexual or larval stage of the parasite (pigs and cattle and taenia)

3. Paratenic host - the parasite does not develop but remains alive and able to infect another susceptible host. (Paragonimus westermani metacercaria in raw wild boar meat * they widen the parasite distribution and bridge the ecological gap between the definitive and intermediate host. 4. Reservoir hosts - they allow the parasites life cycle to continue and become an additional source of human infection. (pigs and Balantidium coli)

D. Vectors - biologic - essential to life cycle - mechanical or phoretic - only transports E. Exposure and Infection (inoculation) (take) - pathogens - carrier - autoinfection - hyperinfection or super infection)

F. Incubation period - period between infection and evidence of symptoms a. clinical incubation period b. biologic incubation period - or prepatent period ; period between infection or acquisition of the parasite and evidence or demonstration of infection

G. Sources of Infection - soil - water - food - raw meat, snails, crabs - vectors - anthropods - mosquitos - bugs, flies - other animals - humans - clothing - self

H. Modes of transmission (Portal of entry) 1. Mouth - most common 2. Skin penetration - Hookworms, Strongyloids, Schistosome 3. Arthropod bites - malaria, filaria, leishmania 4. Congenital transmission - Placental toxoplasma gondii * transmammary - Ancylostoma and Strongyloides 5. Inhalation of air - borne eggs - enterobius 6. Sexual intercourse - Trichomonas

LIFE CYCLE - simple ova - larva - adult

Complicated - several hosts - intermediate hosts - developmental stages in environment or other hosts As the life cycle becomes more complicated the lesser the chances are, for the individual parasite to survive.

Perpetuation of species depends on - ability to ensure transmission thru: a. adaptation to protect itself from host defenses and environment b. overcoming attrition in the species, by producing numerous progeny

- diagnostic stage fertilized ova - infective stage embryonated ova

I. Host - Parasite Relationship Adaptation - led to changes in molecular biology, biochemistry, immunology and structure of the parasite essential to survival A. Locomotory and digestive organs B. Reproductive systems - highly and elaborate - tapeworms - hermophroditic - flukes and tapeworms - asexual reproduction in flukes

C. stream lining - biochemical adaptation parasite can no longer synthesize certain cellular components D. Specialized mechanisms for entry - enzymes - penetration glands - hooklets

A. Effects of Parasite on the host 1. Interference with vital proceses of host through enzyme systems 2. Invasion and destruction of host tissues cutting plates of Hookworms, deposition of schistosome eggs in the liver 3. Deprivation of essential substances to the host 4. Stimulation of host tissue reaction 5. Toxic and allergic phenomenon

B. Effects of the Host on the Parasite 1. Genetic make-up maybe favorable or not to the parasites (sickle cell tract and falciparum malaria 2. Nutritional states - carbohydrate vs. Protein rich diet 3. Immune processes may modify severity of disease in endemic area

Results Resistance ＜virulence patients Resistance ＞ virulence eliminating parasites Resistance ＝ virulence carrier

J. Immunology of Parasitic Infections 1. Immune response a. humoral b. cell mediated

2. Acquired resistance Adaptive mechanisms of parasites to evade host immune response: a. being intracellular in macrophages (Leishmania and Toxoplasma) b. production of variable surface glycoproteins (VSG) trypanosomes c. alternating populations of parasites malaria d. acquisition of host antigens Schistosomes e. Production of proteases

2. 1. Humoral immunity Parasites antigen

2. 2. Cellular immuninty

2. 3. ADCC---Antibody-Dependent Cell. Mediated. Cytotoxicity

3. Immune dependence of drug action The immune response is crucial to the successful treatment of some parasitic infections. * Praziquantel

4. Immunopathology Hypersensitive immune responses a parasite can sometimes cause more harm than the parasite itself 5. Vaccines available against Ancylostoma caninum for dogs Babesia for cattle Leishmania major for humans

Use of Vaccine 1. Prophylactic - anti-infection 2. Transmission blocking - targets development 3. Anti-pathology - down regulates immunopathology

K. Parasite Diagnostic Procedures 1. Fecal examination a. Specimen collection and handling a. 1 wide mouth container a. 2 uncontaminated a. 3 use of laxatives a. 4 liquid specimen - must be examined within 30 mins. or put in preservatives

a. 5 formed specimen - several hours/same day a. 6 multiple collections for several days to optimize diagnosis

b. Specimen Processing b. 1 wet mount b. 2 concentration procedures - Zn. SO 4 flotation - formalin-ether sedimentation c. Permanent stains Dx of intestinal protozoan infections fixatives - Schaudinn’s - PVA

1. trichrome

2. hematoxylin

d. Preservation of feces - PVA - 5 -10% formalin - formal-saline e. Special procedures 1. Culture media - some protozoan 2. Larval hatching - helminths 3. Kato thick smear - examination of large amount of feces

2. Blood examination A. Thick smear B. Thin smear C. Blood concentration procedures 1. Knott’s technique - microfilariae 1 ml. Blood in 10 ml of 2% formalin when centrifuged, RBC are lyzed and only WBC and microfilariae remains maybe allowed to dry on slides and stained with hematoxylin or giemsa

Transmission and Prevention of Parasitic Diseases The basic Factors of transmission: 1. The source of the infection 2. The routes of transmission 3. The presence of a susceptible host

The preventive measures of parasitic diseases 1. Controlling or eliminating the source of the infection 2. Interventions at the routes of transmission 3. Protecting the susceptible hosts