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