TYPHOID FEVER (Salmonella typhi)

by

Ngouagna Edwin Longchi, 

Medical Laboratory Sciences, 

Scientific Journal Club, 

Faculty of Health Sciences, 

University of Bamenda, Cameroon.

edwinlongchingouagna@gmail.com

What is typhoid fever?

Typhoid fever is an infectious disease caused by the rod shaped Gram-negative bacterium Salmonella typhi. It is also known as enteric fever, or commonly typhoid.

Typhoid fever is clinically indistinguishable from paratyphoid fever, which is caused by any of the three types of Salmonella enterica (S. typhi, S. typhimurium, S. enteritidis). Incubation period is 10 to 14 days.

Pathogenesis.

Origin.

Life cycle

Brief Origin.

     In 430BC, a plague which some believe to have been typhoid  killed one-third of the population of Athens, the ancient historian Thucydides contracted the disease but survived to write about the plague.

It was originally  isolated in 1880 by Karl Joseph Erberth.

Life cycle.

It is not known to infect animals (i.e.  It is anthroponostic).

It is a multi-organ pathogen that inhabits the lymphatic tissues of the small intestine, liver, spleen and blood stream of infected humans producing toxins.

Invasion of epithelial cells stimulate the release of proinflammatoy cytokines that stimulate an inflammatory reaction.

The acute inflammatory response causes diarrhea and may lead to ulceration and destruction of the mucosa.

Mode of transmission.

Contaminated food (fecal-oral route).

Water supplies.

Close contact with infected host.

Working or travelling to areas where the illness is endemic.

Having a weakened immune system, then drink salmonella contaminated water.

Chronic carriers.

These are people who still harbor typhoid bacteria and can still contaminate food and water even after receiving antibiotic treatment and proving to be free of symptoms. salmonellae persist in the gall bladder

SIGNS & SYMPTOMS.

First stage.

ž  High fever 39^∘c to 40^oc.

ž  Headache.

ž  Poor appetite.

ž  Generalized aches and pains.

ž   weakness, and fatigue.

ž  Diarrhoea.

ž  rash(rose colored spots on the chest and abdomen).

    Second stage.

ž  High fever of aboout 40^oc.

ž  Delirium(State of violent mental agitation).

ž  Widal test is positive.

ž  Frequent afternoon fevers.

       Third stage.

ž  Intestinal hemorrhage due to bleeding in congested Payer’s patches.

ž  Intestinal peforation.

LABORATORY DIAGNOSIS.

Isolation of bacterium from an appropriate clinical sample e.g. blood, serum, urine, bone marror aspiration, stool(for gastroenteritis, Gram test is used).

Biochemical test: identification of the genus Salmonella.

Serologic testing (Widal test). Here, a serial dilution is made using serum tested against antigens from representatives Salmonella species. The highest diluted serum with positive result is taken as a titer.

High or rising titer to O antigen (≥ 1:160) suggests active infection

High or rising titer to H antigen (≥ 1:160) suggests past infection or immunization.

High titer to the Vi antigen occurs in some cases

Causes of false positive Widal test
 Malaria infection
 other acute febrile illness
 Poor quality reagent
Causes of false negative Widal test
 Specimen collected after antibiotic administration
 Specimen collected at early stage of diseases
 Technical errors.

 There is also a Slide agglutination test/ Kauffman-White system
Used to identify unknown cultures with known sera and important for preliminary identification
of culture.

Required: Salmonella O and H polyvalent antiserum
Method: Mix known sera with unknown culture on a slide.

 Clumping occurs within a few seconds in positive result

      Faeces, blood, or other specimens can also be cultured on:

 Several Non Selective media e.g. nutrient broth.

 Selective media e.g. bismuth sulfide, favor growth of Salmonella

Enrichment media e.g. selenite F broth, Inhibit replication of normal intestinal flora and
permit replication of salmonella.

Differential media e.g Mac Conkey agar for isolation of lactose non-fermenters.

     Any growth is subsequently subcultured onto various agars.

The biochemical reaction of suspicious colonies are then determined on triple sugar agar and lysine-iron agar and a concrete identification is made.

Treatment.

 For cases,
Chloramphenicol
Fluoroquinolones
3rd generation cephalosporins
 For carriers,
Ampicillin followed by cholecystectomy

Cefixime (recommended for children) 

Cholecystectomy (Surgical removal of the gall bladder) in chronic cases.

Prevention.

Have good drinkable water.

Good food supplies.

Wash hands before and after visiting the toilet.

Wash hands before and after eating.

Government provides good waste management and water purification.

Proper treatment of the sick.

Vaccination.

Two licensed vaccines are used:

  Oral live Ty21a vaccine avirulent mutant strain of S. typhi in high endemic areas

  Injectable acetone-killed S. typhi suspensions.

Figure 1: Water filter.

Hope you  own a water filter if not rush and get one.

REFERENCES

Salmonella- medical microbiology: university of Texas medical branch.

Salmonella typhi enterica, David, V. Pollack.

Medical Bacteriology: Ethiopia public health Abilo Tadesse, Meseret Alem

Kayser, Medical Microbiology © 2005 Thieme.

Typhoid fever Wikipedia.