ENTERIC FEVER

Prabin ShahBScMLT, MSc(Biochemistry)

Enteric fever 2

Typhoid fever, commonly just typhoid, is a

common worldwide illness, transmitted by the ingestion of food or water contaminated with the feces of an infected person.

This fever received various names, such as gastric fever, the bends, abdominal typhus, infantile remittent fever, slow fever, nervous fever, pathogenic fever, etc.

INTRODUCTION

The salmonella bacilli was first described by Salmon and Smithin the year 1885.

In 1906, Irish immigrant Mary Mallon worked as a cook and was a carrier. Thus earned the nickname "Typhoid Mary. She died of a stroke after 23 years.

History

The term enteric fever or typhoid fever refers to a communicable disease, found only in man and includes both typhoid fever caused by S.Typhi and paratyphoid fever caused by S.Paratyphi A, B and C .

It is an acute generalized infection of the reticulo-endothelial system, intestinal lymphoid tissue, and the gall bladder.

DEFINITION

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GNB Motile Non sporing Non capsulated

MORPHOLOGY

6

Killed at 60°C in 15 mins

Boiling, chlorination of water and pasteurisation of milk also destroys the bacilli.

Survive in water and ice for weeks

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RESISTANCE

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3 types of antigens;1. Flagellar antigen ‘H’2. Somatic antigen ‘O’3. Surface antigen ‘Vi’

ANTIGENIC STRUCTURE

"O"-group

Sero type "O" antigensPhase 1 (motile)

"H" antigens

Phase 2 (non-motile) "H"

antigensOld New

A 2 S.Paratyphi A 1,2,12 a no phase 2 antigen

B 4 S. Paratyphi B 1,4,5,12 b 1,2

  S. Typhimurium 1,4,5,12 i 1,2

C1 7 S. Paratyphi C 6,7 c 1,5

  S. Colerae-suis 6,7 c 1,5

C2 8 S.muenchen 6,8 d 1,2

S.newport 6,8,20 e, h 1,2

D 9 S. Typhi 9,12,Vi d no phase 2 antigen

  S. Enteritidis 1,9,12 g,m no phase 2 antigen

  S. Gallinarum 1,9,12 no phase 1 antigen no phase 2 antigen

  S. Pullorum (1),9,12 no phase 1 antigen no phase 2 antigen

E1 3,10 S. Anatum 3,10 e,h 1,6

H antigen( flagellar antigen)Ag is present in the flagellaHeat labile proteinStrongly immunogenicProduces large, loose, fluffy clumps.

O antigenLipo polysaccharideIdentical to endotoxinHeat stableProduces compact, chalky, granular clumps.Less immunogenic

Vi antigen

Surface antigen enveloping the O Ag is

referred to as Vi Ag.

Heat labile

Acts as virulence factor by inhibiting

phagocytosis, resisting complement activation

and bacterial lysis.

Poorly immunogenic.

Not helpful in the diagnosis of enteric fever.

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1. ENTERIC FEVER

i. TYPHOID FEVER

ii. PARATYPHOID FEVER

2. SEPTICAEMIA

3. GASTROENTERITIS

PATHOGENESIS

1. TYPHOID FEVER

The name typhoid was coined by Louis in 1829.

Caused by S.typhi

Acquired by the ingestion of contaminated food and

water

IP: 7-14 days

ENTERIC FEVER

Enteric fever is endemic in all parts of india.

Typhoid fever occurs in 2 epidemiological types;

1. endemic( occurs through out the year)

2. epidemic( occur in endemic or non-endemic areas)

Epidemiology

1. Convalescent carriers shed the bacilli in feces for 3 weeks to 3 months.

2. Temporary carriers Shed the bacilli for more than 3 months but less than a year.

3. Chronic carriers Shed the bacilli over an year

4. Fecal carrier the bacilli that persist in kidney or gall bladder are eliminated through feces

5. Urinary carrier bacilli eliminated through urine, associated with urinary lesion such as calculi.

Types of carriers

Bacilli attaches to the epithelial cells of the

intestinal villi in the small intestine.

Penetrates to the lamina propria and sub mucosa

Phagocytosed by the neutrophils and macrophages

Bacteria resists and it enters into the mesenteric lymph nodes and multiply there via the thoracic

duct and enters into the blood stream.

A transient bacteremia follows and the internal organs like liver, gall bladder, spleen, bone marrow,

lungs and kidney get infected.

Sequence of infection

Clinical features include; Mild pyrexia Headache Malaise Anorexia Coated tongue Abdominal discomfort with

constipation/diarrhea Congestion of mucous membranes Hepatosplenomegaly with soft and palpable

spleen. Step ladder pyrexia with relative bradycardia

and leucopenia. Skin rashes known as rose spots may appear

on the 2nd and 3rd week.

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Rose spots

2. PARATYPHOID FEVER

Milder form than typhoid fever. Caused by S.paratyphi A,B and C

Other salmonella causing enteric fever are;

S.dublinS.bariellyS.sendaiS.enteritidisS.typhimuriumS.eastbourneS.saintpaulS.panama

I. Specimen collection

BloodFaecesUrineAspirated duodenal fluidBileBone marrowRose spotsPus from suppurative lesionsCSFSputumAt autopsy cultures may be obtained from the gall bladder, liver, spleen, and mesenteric lymph nodes.

LAB DIAGNOSIS

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Duration of disease Specimen examination

% positivity

1st week Blood culture 90

2nd week Blood cultureFaeces cultureWidal test

7550Low titre

3rd week Widal testBlood cultureFaeces culture

80-1006080

Specimens collection based on different phases of enteric fever

Gram stain is done

GNBNon capsulatedMotile with peritricous flagella except gallinarum and pullorum.

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II. Microscopy

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Grows on ordinary media Opt temp: 37°C pH: 6-8 Aerobic and facultative anaerobic.

On nutrient agarColonies are 2-3mm in diameter, circular, translucent, grey white in color, low convex and smooth.

III. Culture

On MacConkey’s agar and DCAColorless colonies due to NLF colonies.

Selective mediaWilson and Blair bismuth sulphite medium

Jet black colonies with metallic sheen are formed due to formation of hydrogen sulphide.

Xylose lysine deoxycholate (XLD)Red colonies with black centres are seen

Enrichment mediaSelenite F brothTetrathionate broth (TTB)

Ferments glucose and mannitol forming acid and

gas except S.typhi produces only acid but no gas. Catalase positive Oxidase negative Indole is not produced

Produces H2S in TSI agar except S. paratyphi A

and S. cholerae-suis. Utilise citrate (except S.typhi & S.paratyphi A) MR positive VP negative Urea not hydrolysed Nitrate reduction test is positive

IV. BIOCHEMICAL REACTIONS

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S.typhi

S.Paratyphi A

S.Paratyphi B

S.Paratyphi C

Glucose A AG AG AG

Mannitol A AG AG AG

Lactose - - - -

Sucrose - - - -

Indole - - - -

Citrate - - + +

MR + + + +

VP - - - -

H2S + - ++ +

Biochemical rxns to differentiate btw salmonella species

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Positive in 90% of the cases in the first week of fever. 75% in second week 60% in third week

Procedure

10ml of blood collected under aseptic conditions and transferred into blood culture bottles.

Blood culture

Blood has to be diluted with the culture media in

the ratio of 1:10.

Then incubated at 37°C overnight.

Subculture done on BA and MCA

More preferred method is the Castaneda’s method of blood culture.

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Salmonella are shed in faeces during the infection and

convalescence phase too.

Generally faeces culture turn positive in the second

week of infection.

Sample is inoculated into one tube each of selenite

and tetrathionate broth(enrichment media)

Plated onto MCA, DCA, XLD, and Wilson-Blair medium.

Faeces culture

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Frequency of getting a positive result is less

when compared to that of blood and faeces.

Generally seen as positive in the 2nd and 3rd

weeks.

Urine samples are centrifuged and deposit is

inoculated into both enrichment and selective

medium.

Urine Culture

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5ml of blood is withdrawn aseptically into

sterile container and allowed to clot.

Clot is broken up with a sterile glass rod and added to bile broth containing streptokinase(100units/ml) which digests the clot causing its lysis and thereby the bacteria are released from the clot.

Clot culture

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It is an agglutination test for the detection of

agglutinins (H and O) in patients with enteric fever.

The antibodies begin to appear in serum at the end of 1st week and rise during the 3rd week of enteric fever.

2 specimens of sera are collected at an interval of 7 to 10 days to demonstrate the rising Ab titre.

WIDAL TEST

2 types of tubes; Dreyer’s tube Felix tube

Equal vol of 0.4ml of serial dilution of the serum(1:10 to 1:640) and the H and O antigens are mixed and incubated at 37°C for 4 hrs and read after overnight incubation in room temp.

Control tubes with antigen and normal saline are included to check for auto agglutination.

Procedure

H agglutination - formation of loose, cotton wool clumps

O agglutination – granular deposit at the bottom of the tube

High dilution with carpet formation indicates the antibody titre against that particular Ag.

Control tubes will show a compact deposit (button formation).

A loopful of the growth from nutrient agar slope is emulsified in 2 drops of saline on a slide.

One emulsion acts as a control and other as a test.

Agglutination is first carried out with the polyvalent O and the polyvalent H antisera.

Positive agglutination indicates that the isolate belong to genus salmonella.

Then if S.typhi is suspected, agglutination with O anti serum is done.

Prompt agglutination indicates that the isolate belong to group D salmonella.

S.typhi is confirmed by the agglutination with O anti serum.

SLIDE AGGLUTINATION TEST

Vaccinations

i. TAB vaccine heat killed Polyvalent vaccine Dose schedule: 2 doses of 0.5ml at an interval of

4-6 weeks S/C followed by booster every 3 years.

ii. Purified Vi polysaccharide vaccine(typhim-Vi) Dose schedule: single dose of 25µg injected I/M or

S/C Causes minimal reaction.

PROPHYLAXIS

iii. Live Oral typhoid vaccine

Stable mutant of S.typhi

Dose schedule: 3 doses on days 1,3,5 should be taken an hour before food, with a glass of water or milk.

Oral (typhoral) vaccine is available as capsule.

On ingestion, it initiates infection but self destructs after 4-5 cell divisions and thus cannot induce any illness.

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Antibiotics such as;

Chloramphenicol Streptomycin Tetracycline Ampicillin Amoxycillin Cotrimoxazole

Are found effective in the treatment of typhoid fever.

Treatment

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Showed resistance to chloramphenicol.

Chloramphenicol resistant typhoid fever

appeared in kerala in 1972.

Multi drug resistant S.typhi is also becoming a

major problem in india.

These may cause nosocomial salmonellosis as

septicaemia, meningitis, and suppurative lesions.

Drug resistance

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A zoonotic disease

Caused by S.typhi, S.typhimurium,

S.enteritidis, S.indiana, S.newport, S.agona.

Sources: poultry, meat, milk, eggs.

Clinical features: diarrhea, vomiting, fever,

abdominal pain.

Gastroenteritis

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Certain salmonella may cause septicaemia with

suppurative lesions such as deep abscess,

osteomyelitis , pneumonia, endocarditis and

meningitis.

S.cholerae suis is the most important causative agent

of salmonella septicaemia.

Fulminating blood infection.

Treatment with chloramphenicol.

Septicaemia

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1. Text book of microbiology

Ananthnarayan and Paniker’s

2. Text book of microbiologyC.P. Baveja

3. Mackie and McCartney4. google

REFERENCE

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