Download Infectious Diseases

Infectious
Diseases
Definitions
Disease ≡ a disordered or incorrectly
functioning organ, part, structure, or system
of the body resulting from the effect of
genetic or developmental errors, infection,
poisons, nutritional deficiency or imbalance,
toxicity, or unfavourable environmental
factors.
Infectious Disease ≡ Any disease caused by the
entrance, growth, and multiplication of
microorganisms in the body. It may not be
contagious.
Non – infectious Disease ≡ Diseases that are
not caused by a pathogen and cannot be shared
from one person to another. May be caused by
either the environment, nutritional deficiencies or
genetic inheritances.
– Eg. Environmental causes such as skin cancer from
radiation, or lack of food e.g. Scurvy
Cholera
Infectious agent: Vibrio cholerae
Transmission: Through ingestion of
vibrio-contaminated water, food
Incubation : 1 – 5 days
Site of action of pathogen: wall of small
intestine
The bacteria releases a toxin that causes
increased release of water in the
intestines, which produces severe
diarrhea.
Cholera occurs in places with poor
sanitation, crowding, war, and famine.
There are an estimated 3–5 million cholera
cases and 100 000–120 000 deaths due to
cholera every year.
Occurrence (1997)
Occurrence key: yellow = low, orange = medium, and red = high
Up to 80% of cases can be successfully
treated with oral rehydration salts.
Provision of safe water and sanitation is
critical in reducing the impact of cholera
Oral cholera vaccines are considered an
additional means to control cholera, but
should not replace conventional control
measures.
poor surveillance and fear of international
stigmatisation and sanctions lead to
underreporting of official numbers by
affected countries.
increasing spread of cholera in recent
years may reflect
– a lack of international quarantine enforcement
by some countries which also have primitive
public water supplies and inadequate sanitary
regulations,
– the international mobility of carriers in the
world's population,
– and the quick transport of contaminated food
and water by ships and aircraft.
Cholera can cost governments billions of
dollars to eradicate.
Absenteeism by the workforce caused by
cholera adversely affects industrial output.
Cholera outbreaks can adversely affect
tourism
Cholera outbreaks may lead to loss of
trade.
Measles
Causative agent: Morbillivirus
Transmission: air-borne
Incubation period: 3-7 days for rash to
appear
Site of action: highly contagious infection
of the respiratory system.
Prevention and control
Treatment - bed rest, fluids and medicine
for fever and headache.
Prevented with measles vaccine.
Recommended for children at 12 months
of age. This shot is given as measles,
mumps, rubella (MMR) vaccine.
Vaccination
Between 2000 and 2007, 576 million children
were vaccinated against measles, resulting in
a 74 percent decrease in measles-related
deaths worldwide.
Education and availability of vaccine will
decrease deaths further
Problems with eradicating measles:
(1) the role of humans in maintaining
transmission,
(2) the availability of accurate diagnostic
tests,
(3) the existence of effective vaccines,
(4) lack of political will in some
industrialized countries,
(5) increasing urbanization and population
density,
(6) the HIV epidemic,
World occurrence
Mortality in developed countries is
~1/1000. In sub-Saharan Africa, mortality
is ~10%.
On average, ~450 children die every day
from measles.
factors contributing to continued
transmission:
– Lack of infrastructure,
– inadequate health care systems,
– lack of funds
Malaria
Causative agent: Plasmodium falciparum,
P. vivax, P. ovale, P. malariae
Transmission: female anopheles mosquito
Incubation period: 1 week to a year
Site of action of pathogen: liver, red blood
cells, brain
Prevention and control
Protective clothing over the arms and legs,
screens on windows,
insect repellent.
Education to cover over areas of stagnant, still
water
Chloroquine is the drug of choice for protecting
against malaria. But Falciparum malaria is
becoming increasingly resistant to anti-malarial
medications.
People who are taking anti-malarial medications
may still become infected.
Prevention cheaper than cure but the
capital costs required are out of reach of
many of the world's poorest people.
estimates that malaria can be controlled
for US$3 billion in aid per year.
Malaria stays in an area due to
– high human population density,
– high mosquito population density
– high rates of transmission from humans to
mosquitoes and from mosquitoes to humans.
Many countries are seeing an increasing
number of imported malaria cases owing
to extensive travel and migration.
Occurrence
Endemic in a broad band around the
equator, in areas of the Americas, many
parts of Asia, and much of Africa;
however, it is in sub-Saharan Africa where
85– 90% of malaria fatalities occur.
300-500 million cases of malaria each
year, and more than 1 million people die
from it.
Tuberculosis
Causitive agent: Mycobacterium
tuberculosis, M. Bovis
Transmission: airborne droplets,
unpasteurised milk and meat
Incubation period: few weeks or months
Site of action of pathogen: primary
infection in lungs, secondary infection in
lymph nodes, bones and gut.
The immune system "walls off" the TB bacilli, which is
protected by a thick waxy coat, can lie dormant for years.
When someone's immune system is weakened, the
chances of becoming sick are greater.
Prevention and control
Detection of infected individuals and
treatment of them.
Mass vaccination of children
Treatment long term – 6 to 24 months
Stopping treatment early causes resistant
strains
Poor people can’t afford it
Leading cause of death of people with HIV
Occurrence
An estimated 1.7 million people died from
TB in 2009. The highest number of deaths
was in the Africa Region.
2000 – 2004 20% increase in resistance
Overall, one-third of the world's population
is currently infected with the TB bacillus.
AIDS
Causative agent: HIV virus
Transmission: during sexual intercourse,
blood transfusions, across the placenta, in
breast milk, in blood in infected needles
Incubation period: few weeks to 10 years
Site of action of pathogen: T helper
lymphocytes, macrophages and brain cells
Unprotected sex is HIV's main route into
humans, where it targets the white blood
cell known as CD4.
The virus replicates inside, eventually
bursting out and flooding the body in the
billions.
The immune system then kicks in, and the
body and the virus wage all-out war.
During the height of battle billions of CD4
cells can be destroyed in a single day.
As the cell count drops, the immune
system begins to fail and opportunistic
infections such as tuberculosis take hold.
Prevention and control
Treatments But No Cure
prevention focuses on sex education and the
use of condoms.
treatments combat its onset.
– Antiviral drugs work by slowing the replication of HIV
in the body. These drugs need to be used in
combination because the virus readily mutates,
creating new and often drug-resistant strains.
– Such treatments are expensive, however, and are still
denied to millions of people in the developing world.
Researchers are currently working on an AIDS
vaccine.
Poverty; inadequate health care and
education, and promiscuity have all been
highlighted to explain Africa's AIDS
nightmare.
Occurence
AIDS today is a global pandemic affecting every
country.
In 2006, an estimated 39.5 million people had
HIV/AIDS. Almost three million of them died.
Sub-Saharan Africa accounts for two-thirds of
the world's HIV cases and nearly 75 percent of
deaths due to AIDS.
Infection rates in Zimbabwe's adult population
exceed 20 percent, while in Swaziland a third of
adults are HIV-positive.
Smallpox
Causative agent: Variola major and
Variola minor
Transmission: inhalation of infected air
droplets, direct contact with infected bodily
fluids or contaminated objects such as
bedding or clothing.
Incubation period: 12 – 14 days
Site of action of pathogen: in small blood
vessels of the skin and in the mouth and
throat.
Antibiotics
Two types:
– Broad spectrum
– Narrow spectrum
They show selective toxicity – killing the
pathogen but not damaging the host cell.
How they work
The Greek word anti means "against",
and the Greek word bios means "life"
1. Prevent the bacteria
from forming cell walls
during reproduction.
This leads to osmotic
lysis. Only work on
growing bacteria not
dormant ones.
2. Inhibit protein synthesis by binding to
bacterial ribosomes
3. Disrupt synthesis of nucleic acids.
4. Disrupt cell membranes.
Essay
Discuss the role of epidemiology in
determining patterns of disease. Illustrate
your answer with specific examples of
named diseases.
20 marks