Transcript Slide 1

•Typhoid fever ( also known as enteric fever) is a
bacterial infection occurring in the intestinal tract
and occasionally, in the bloodstream.
•It is caused by the bacterium Salmonella typhi -a
unique human strain of salmonella. It is a rod
shaped, gram negative bacterial pathogen, being
motile with the aid of flagellum.
•In nature, S. typhi is often found on open sewage
and in the gut of animals.
•Typhoid fever cases are most common in areas
within Asia, Africa and Latin America, therefore a
greater risk lies in travellers to those regions
being affected by the disease.
The bacterium Salmonella typhi
How is it spread?
•Transmission of the bacterium often occurs when food
or water is contaminated by carriers of the disease and is
then digested by others.
•Typhoid can also be transmitted by flies landing on
open sewage, picking up the bacteria, and then
contaminating food, which is again eaten by humans.
Spreading in this way is known as indirect host-host
transmission.
Flies carry disease by picking up infectious
agents on their feet
Creating Cultures
Blood Cultures: used to determine the presence of
microorganisms such as bacteria in the blood.
•A blood sample from the individual is placed in a special
laboratory preparation and incubated for up to seven days.
• It is important that the conditions within the environment are
controlled to avoid contamination.
•If organisms are observed in the sample, it may be cultured
further, and a Gram stain may also be done in order to determine
the particular organism, so that antibiotic courses can be started
for the affected individual.
•Approximately 80% show a positive result, usually in the first
week of infection.
Identifying salmonella typhi
As isolating a pathogen is not always possible in order to
identify the possibility of infectious disease, an antibody
titer is performed. ‘Titer’ refers to quantity. Generally, the
method involves a serial dilution of serum from the
individual concerned. The highest dilution at which the
antigen-antibody reaction occurs is the point at which any
sign of infection is determined. One way of measuring
antibody titer is:
•Agglutination which refers to the resulting mixture
formed when a particular antigen and antibody specific for
that antigen is mixed. It is observed as a visible clumping
of the antigen..
Stool/ Faecal Culture: used in a laboratory as a test
to isolate and identify pathogenic organisms present,
which may cause gastrointestinal symptoms and
disease-in this case S. typhi.
•Growth of microorganisms is encouraged by placing
a sample in a culture medium.
•At regular intervals, the culture is observed for
growth. Growth enables the organism present to be
identified further tests
•Stool cultures show a positive result at later stages
of the infection, usually in 30-60% of cases.
•Bone marrow and urine cultures may also be carried
out.
ELISA (enzyme-linked immunosorbent
assay)
This is a more effective means of identifying
pathogens. It uses antibodies to which enzymes are
attached to, leading to both the catalytic activity of
the enzyme and the specificity of the antibody to be
unchanged. There are two methods:
•Direct ELISA- detects antigens
•Indirect ELISA- detects antibodies
For human serum, either of the above methods are
used, depending on which is being detected.
•After ingestion, S.typhi travel down the digestive where they are taken in by phagocytes. These are important cells
within the immune system, engulfing and destroying ‘foreign’ bacteria and viruses invading the body.
•However, S. typhi are able to resist this process and rapidly multiply inside the phagocyte. The time period taken to do
this is the 10-14 day incubation period of typhoid fever.
•The cell then bursts, causing the huge numbers of bacteria to spill into the bloodstream. It is then that symptoms of
typhoid fever begin to show.
• The bacteria then begin invading certain tissues of the intestine. This eventually leads to perforation of intestine,
which then in turn results in peritonitis -leakage of the intestinal contents-and can cause death.
•Other effects of typhoid fever include liver and spleen enlargement. Meningitis and brain infections may occur in the
most sever cases and may even lead to coma.
Symptoms
•High fever
•Diarrhoea
•Headaches
•Constipation
•Possible outbreak of ‘rose spots’-a rash of
rose coloured spots, characteristic of typhoid
fever.
•Slow heart rate (bradycardia)
•Muscle pain (myalgia)
•Extreme symptoms include intestinal
perforation, spleen and liver enlargement.
Image showing perforation
of the small intestine.
Example of ‘rose spots’ on an affected
individual
•The most common method of treating
typhoid is through a course of Penicillin
or Quinolone based antibiotics, primarily
ampicillin and ciprofloxacin respectively.
The antibiotic chloramphenicol is also
used.
•Intravenous fluids and electrolyte
therapy may also be given to replace
fluids and salts lost due to diarrhoea. This
is especially important for children
suffering with typhoid fever.
•Research shows that Cefpodoxime-’an
oral third generation cephalosporin’ seems
an effective molecule in its activity against
salmonella species within paediatric
typhoid fever. However limitation lies in
the lack of clinical trials carried out.
• Experiment with a live, attenuated
vaccine for typhoid is also underway and
shows possible success.
•Immediate treatment with antibiotics
means the fatality rate is reduced to
about 1%.
Map showing the areas affected by typhoid
As the spreading of typhoid fever occurs
mainly through poor sanitation, public
education campaigns promote the washing of
hands after using the toilet as well as prior to
handling food. These are essential ways of
controlling the transmission of salmonella
typhi and therefore preventing the risk of
typhoid fever.
•Adequate water treatment, waste disposal
and the prevention of food supply
contamination is necessary.. This means that
carriers of the disease must not work as food
handlers.
•The filtration and chlorination of water as a
method of purification has also proved very
successful in reducing the risk of typhoid
fever.
Spreading of the disease can also be prevented
by isolating individuals with active diarrhoea, who
are unable to control their bowels i.e. infants,
certain handicapped people. This is due to the
fact that the bacterium can be passed in the
faeces of those infected.
Immunisation is encouraged for those travelling
to areas where typhoid fever is endemic, such
as Asia, Africa and Latin America. Currently,
two vaccines are available:
•Typhim Vi: is a killed-bacteria vaccinatio
based on the purified Vi polysaccaride of
salmonella typhi.
•Vivotif/Ty21a: is a live bacteria vaccination,
administrated orally.
Although both vaccines provide protection
against typhoid fever, neither is 100% effective,
nor do they protect against unrelated typhus.
The typhim Vi
vaccine
•However, some people may become an
asymptomatic carrier of typhoid fever, not affected
by the symptoms themselves but having the ability
to infect others.
•It is thought that roughly 5% who initially suffer
from typhoid fever, then carry on the disease after
recovery.
Books
Websites
Brock-Biology of Microorganisms
11th Edition
www.health line.com/gale content/typhoid fever
Authors: M.T.Madigan, J.M Martinko
http://www.who.int/vaccines/en/typhoid.shtml
Articles-Medline
http://www.who.int/infectious-diseasereport/2000/graphs/4_mdr-salmonella.htm
Title: Problem pathogens: extraintestinal complications of
Salmonella enterica serotype Typhi
infection.
http://www.denniskunkel.com/DK/DK/Bacteria/96430B
.html
Authors: D.B.Huang, H.L Duport
http://en.wikipedia.org/wiki/Typhoid_fever
NLM Journal Code: 101130150
http://www.lenntech.com/Waterbornediseases/typhoid.htm
Title: Cefpodoxime - utility in
respiratory tract infections and
typhoid fever.
http://health.utah.gov/epi/fact_sheets/typhoid.html
Authors: A.Aggarwal, S.Rath
NLM Journal Code: gkt, 0417442
http://www.cdc.gov/NCIDOD/DBMD/diseaseinfo/typhoi
dfever_g.htm
http://www.emedicine.com/MED/topic2331.htm