Download 2.2.6. Transmission of Diseases

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 anticoagulant)
 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
