see also:

• clinically important bacteria
• A historians' view of the bubonic plague

• Yersinia are Gram-negative, rod-shaped coccobacillus, a facultative anaerobic bacteria belonging to the enterobacteriaceae family
• Y. pestis is the organism causing the bubonic plague or Black Death epidemic and thousands of cases each year still occur

• see wikipedia
• discovered by Alexandre Yersin in 1894 during an epidemic of the plague in Hong Kong
• most of the spreading occurs between rodents and fleas (the vector) but can be spread person-to-person if in pneumonic form
• the copy number of its pla gene correlates with mortality rate and how soon the person will die ¹⁾
• 30% of human cases worldwide are now in Madagascar which usually sees ~400 new cases per year after Indian steamships brought the plague there in 1898, and is primarily associated with rural areas and agricultural activity, where maximum abundance of rodents in the fields is observed in July and August, followed by the maximum abundance of fleas from September to November
• the Black Death remains the single deadliest pandemic in recorded human history, killing an estimated 30 to 50% of the populations of Europe, Western Asia and Africa as it moved through those regions. Appearing in the 14th century, it re-emerged in waves over more than 500 years, persisting until 1840.
  • this strain broke into two major lineages - one of these two lineages is the ancestor of all present-day strains, the other re-emerged over centuries in Europe and ultimately went extinct by the early 19th century.
• caused the Plague of Justinian, the first plague pandemic which had broken out in the mid-500AD. Strains of the Justinian plague became extinct after 300 years of ravaging European and Middle Eastern populations.
• the third plague pandemic began in China in 1855 and continues today especially in regions like Madagascar and the Democratic Republic of Congo. The majority of strains which continue to circulate today in Africa, South America and India are the more virulent ones, the ones that were previously responsible for massive mortality.²⁾

• 2-6 days incubation
• sudden onset of headache, fever, chills
• extreme weakness, lymphadenopathy (esp. inguinal as most flea bites are on legs) which then form buboes
• death can occur in less than 2 weeks

• gastro-like illness then septicaemic shock, hepatosplenomegaly
• may not have buboes

• pneumonia-like illness
• haemoptysis
• septic shock
• person-to-person spread
• 100% mortality if untreated

• yersiniosis is an uncommon bowel infection which usually causes inflammation around the terminal ileum region causing a terminal ileitis, mesenteric lymphadenopathy or an enterocolitis
• spread to humans by eating food or drinking water contaminated by human or animal faeces, but may also result from contact with infected pets or farm animals
  • avoid drinking unpastuerised milk and maintain good hand hygiene
  • cook meat well, especially pork
• it can also be spread in blood transfusions as it can multiple in stored blood products (Yersinia are iron-loving siderophilic bacteria) - hence people should not donate blood if they have had recent diarrhoeal illness.
• incubation period is 4-7 days after exposure
• usually produce a beta-lactamase and thus are resistant to penicillins and cephalosporins (but ceftriaxone can be used)

• more common in young children
• patients with haemochromatosis are said to be more susceptible to infection
• fever
• diarrhoea which may be bloody esp. in young children
• abdominal pain and cramps
• can mimic appendicitis, Salmonella or shigella

• stool m/c/s or PCR sample

• most cases are self-limiting
• in immunosuppressed patients, it can spread to form abscesses in liver or spleen
• 50% of adults develop joint pains, some as a immune mediated reactive arthritis
• some may develop erythema nodosum
• seems to be associated with autoimmune Graves-Basedow thyroiditis although may not be causal

• stool m/c/s
• supportive care as most cases are self-limiting
• contact precautions as for gastroenteritis
• those with sepsis, severe ill;ness or who are immunocompromised, should be treated with antibiotics such as:
  • doxycycline, plus
  • gentamicin
• exclude infected cases from:
  • childcare, school, work, swimming pools until there has been no diarrhoea for 24hrs
  • however, person may remain infective to others for 2-3 weeks, and, if not treated with antibiotics, may shed in faeces for up to 2-3 months