Shigella : Clinical Findings, Pathogenesis, Lab Diagnosis and Treatment

The drug of choice for shigella is ciprofloxacin.

Shigella is usually resistant to ampicillin and cotrimoxazole.

Ans. is ‘a’ i.e., Large dose is required for infection

SHIGELLOSIS

.Shigella is highly communicable . The infective dose for shigella is less. It can be as low as 10 – 100 bacilli because they survive gastric acidity better than other enterobacteriae.

About option d

.    ” essential process in the pathogenesis is invasion of the mucosal epithelial cells by the organism through phagocytosis. The production of toxin is also of importance for virulence but main factor is invasion of the Epithelial cells of gut by the organism”

.         REMEMBER :

“Non toxigenic mutants can still cause dysentery but not non invasive one”

Ans. is ‘a’ i.e., It can lead to hemolytic uremic syndrome 

• Hemolytic uremic syndrome occurs with Sh. dysenteriae type 1.
• Complications are most often seen in infection with Sh dysenteriae type 1 and include :

–    Arthritis                      – Conjuctivitis                       – Intussusception in children

–   Toxic neuritis            – Parotitis                               – HUS

• Invasive property of shigella does not depend on enterotoxin, It depends on “virulence marker antigen (VMA) encoded by large plasmids.
• Shigella is aerobe and facultative anaerobe.
• Shigella is MR positive.

Ans. is ‘d’ i.e., Shigella Dysentriae 

. The person is suspected to have traveller’s diarrhoea.

. The most common cause of traveller’s diarrhoea is E.coli , but the strains of the E.coli (Enterotoxigenic
& Enteropathogenic) given in the choice do not produce invasive illness i.e presence of blood in stool.

.  It is a feature of Enterohemorrhagic E.coli

.  Now the choice is between Salmonella & Shigella diarrhoea are

. Both these organisms produce invasive disease i.e dysentery or inflammatory diarrhoea . But Shigella & Salmonella can be differentiated on the basis of incubation period.

i)        Shigella                                       (1-2days)

ii)      Salmonella               —)0.         (10-14 days)

Ans. is ‘d’ i.e., Rabbit ileal loop 

.  Enterotoxin (SHET-1 and-2) cause net fluid secretion in ligated ileal loop in vivo and alter electrolyte transport by gut segments in vitro.

. Sereny test is a noninvasive test used for shigella and ETEC —> instillation of a suspension of freshly isolated ETEC or shigella into the eyes of guinea pigs leads to mucopurolent conjuctivitis and severe keratitis.

Ans. is ‘d’ i.e., Vibrio cholera

Hemol^ytic uremic syndrome is caused b^y

 ‑

Ans. is ‘a’ i.e., Staph food poisoning; ‘b’ i.e., Clostridia; ‘c’ i.e., Shigella

 All these organisms (option a to d) can cause diarrhea and stool should be examined for diagnosis. Diagnostic approach to infectious diarrhea

.   After the severity of illness is assessed, the most important distinction that the clinician must make is between inflammatory and noninflammatory disease.

.   Examination of a stool sample is an important supplement to the narrative history.

.   Stool should be examined for blood, leukocytes and mucus.

.   Fecal lactoferrin is a marker of fecal leukocytes and can be detected by later agglutination or ELISA. For options ‘e’

“Since pinworm (E. vermicularis) eggs not usually released in the bowel, the diagnosis cannot be made by looking for eggs in the feces”.

Ans. is ‘c’ i.e., Hepatic failure

o Hepatic failure does not occur in HUS.

Laboratory findings of HUS

o Thrombocytopenia                                                                                     o Leukocytosis

o ARF r BUN and creatinine with oliguria                                                           o Microscopic hematuria

o Peripheral smear Helmet cells, burr cells, fragmental RBCs (Schistocytes).         o Proteinuria

o Hemoglobinuria with hemosiderinuria                                                         o Normal PT and APTT Option ‘b’ requires some explanation here ‑

Though neurological manifestations may occur in HUS, these are not common and this feature differentiated HUS from TTP. In TTP neurological symptom is one of the clinical criteria for diagnosis.

Answer is A or None (Hyperkalemia or None)

Hyperkalemia is the single best answer of exclusion.

HUS may occur with Shigella Dysentriae type I.

Clinical features in HUS due to shigella as mentioned in (Harrison 14th/959) include :

• Oliguria progressing to anuria and renal.failuree
• Drop in hematocrit progressing to severe anemia and CHF^Q
• CNS abnormalities include – encephalopathic symptoms

–  seizures

– altered consciousness – bizzare posturing

• Laboratory : – Profound hyponatremia ^Q and severe hypoglycemia° may be seen

– Leukamoid reactions with increased leucocyte counts ^Qmay be seen

– Thrombocytopenia^Q is common cla

– Although one might argue that hyperkalemia may as well be a feature of HUS on account of renal failure, 1 have excluded it because all other options have been mentioned directly in the standard Harrison text.

Ans. is ‘b’ i.e., Shigella

Salmonella (typhoid) and meningococci cause morbiliform rash. Staphylococcus causes scarlentiform rash in TS S and SSSS.

Infections causing Exanthems (acute generalized rash)

Morbilliform

• Viral : Measles (rubeola), rubella, erythema infectiosum, EBV, CMV, adenovirus, echovirus, early HIV, coxasackie virus.
• Bacterial : Typhoid, Early secondary syphiis, Early rickettsia, Early meningoccemia.

Scarlentiform

• Scarlet fever (streptococcus).
• Toxic shock syndrome.
• Staphylococcal scalded skin syndrome.