2.2.6. transmission of diseases learning outcome: describe the causes and means of transmission of...
TRANSCRIPT
2.2.6. Transmission of Diseases
Learning Outcome:
Describe the causes and means of transmission of malaria, HIV/AIDS and TB
Methods of Disease Transmission Droplets – coughing & sneezing Faecal/Oral – usually from food &
drink Direct physical contact – touching,
kissing, sexual intercourse Indirect contact – touching a
contaminated object Vector transmission – by an insect or
other creature
Malaria - parasite Caused by a protozoan parasite of the
genus Plasmodium Mainly P. falciparum but other species
include P. vivax, P. ovale and P. malariae
P. knowlesi can cross the species barrier from monkeys to humans
The parasite lives in subtropical areas of Africa, Asia and the Americas
ELECTRON MICROGRAPH OF PLASMODIUM PARASITE
RING STAGE OF PLASMODIUM FALCIPARUM
Spread of Malaria Mainly transmitted via the vector
method The female Anopheles mosquito feeds
nocturnally on blood It transfers the sporozoite phase of the
parasite from its salivary glands to the host (mosquito saliva acts as an anti-coagulant)
If the host already has malaria the mosquito sucks up the gamete stage of the parasite
Zygotes develop in the mosquito
Life Cycle of Plasmodium
Other means of malarial transmission
It is also possible to spread the parasite via unhygienic conditions mainly in a hospital environment
Unsterilised needles and unscreened blood transfusions also play a part
The parasite can also pass across the placenta from mother to foetus
HIV/AIDS cause Human Immunodeficiency Virus The virus can sit dormant for many
years (HIV Positive stage) Once active it destroys T helper cells
rendering the immune system ineffective
Then the person has Acquired Immune Deficiency Syndrome
Death usually soon follows due to secondary infections
HIV Transmission Rectal, vaginal or oral sex Intravenous drug use – reusing
syringes Blood transfusions from unscreened
donors In Utero / Perinatal from mother to
foetus Breast feeding can also spread the
virus
Tuberculosis - Cause Causative agent is a rod-shaped
bacterium Mycobacterium tuberculosis or M.
bovis are the main species There are many other species that
can cause symptoms Over 2 billion people are infected
with TB worldwide Mostly the body’s immune system is
able to keep the disease at bay
Tuberculosis - Transmission Transmitted by the droplet method Needs prolonged contact with a carrier
or sufferer to become infected Infected meat or milk of cattle Conditions of deprivation makes
infection more likely Overcrowding Poor health or diet Inadequate ventilation