Lecture 39 - Bacillus And Brucella - 7 Nov 2006

BACILLUS and BRUCELLA

Objectives At the end of the lecture the students should be able to: Describe the specific features of the genus Bacillus and Brucella Recall the infections caused by them Discuss their epidemiology Understand the pathogenesis of infections Recall the laboratory investigations Recall the management and prevention

BACILLUS Gram-positive, spore-forming Found in the soil and water Airborne contaminants in microbiology laboratories – Except B. anthracis

Important species: – B. anthracis causes anthrax – B. cereus causes food-poisoning

Bacillus anthracis Gram-positive bacillus Spore-forming Capsule - Polyglutamic acid

ANTHRAX - epidemiology Enzootic Domestic herbivores – sheep, goats, and horses Transmission to humans by: – Contact with infected animal products – Inhalation of contaminated dust – Ingestion

Initiation of infection – s.c. inoculation of spores through skin abrasions Spores – highly resistant Animal carcasses - buried 6 feet deep

ANTHRAX Pathogenesis Capsule – antiphagocytic Not immunogenic by itself Two plasmid-mediated exotoxins – Edema factor – Lethal factor

The exotoxins elicit protective antibodies

ANTHRAX Clinical types Cutaneous Pulmonary Gastrointestinal

Cutaneous anthrax 95% of human cases Spores - skin abrasion  papule develops  rapidly  painless, black, severely swollen “malignant pustule”  crusts ESCHAR Invasion of regional lymph nodes Lymphatic duct and blood stream  fatal septicemia Overall mortality of untreated cases – 20%

Pulmonary anthrax “Woolsorter’s disease” Inhalation of spores Multiplication in the bronchi  lungs  lympathatics  bloodstream – – –

Inflammation Progressive hemorrhagic lymphadenitis Septicemia

Mortality rate is almost 100% Biological warfare

Gastrointestinal anthrax Caused by ingestion of spores Eating raw or inadequately cooked meat containing B. anthracis spores – Haemorrhagic diarrhoea, septicemia – Rapid death

Occurs among Pastoralists Episodes occur in small outbreaks in a family or village

Laboratory identification Blunt-ended Gram-positive bacilli Sporulates only in cultures Non-motile, encapsulated in vivo Capsule stains with polychrome methylene blue  McFadyean

reaction Suspected sample should be handled with extreme care in the laboratory

Treatment and Prevention Penicillin Ciprofloxacin Doxycycline Autoclave - most reliable means of decontamination Cell-free vaccine for workers at high-risk occupations – Goat hair and woolen mill workers – Live-stock handlers – Military

Bacillus cereus Produces tissue-destructive exotoxin Causes food-poisoning by enterotoxin – Emetic or diarrhoeal effects – Diarrhoeal effect has a cAMP-stimulatory mechanism like cholera toxin – Associated with reheated Chinese food e.g. Chinese rice.

Heat-stable toxin  vomiting within 1-5 h Heat-labile enterotoxin  diarrhea within 10-15h

Other Bacillus species Implicated in opportunistic infections Trauma or placement of artificial devices and catheters – e.g. B. subtilis

B. stearothermophilus – used as biological indicators of effective heat sterilization by including filter paper strips carrying the spores into the autoclave cycle

Brucella Small Gram-negative coccobacilli Intracellular pathogens Growth enhanced by erythritol in placenta of animals but not in man Species characteristically associated with animals Causes Brucellosis B. abortus – cattle B. melitensis – goats and sheep B. sius – pigs B. canis - dogs

Brucellosis B. abortus – Infects cows worldwide – Mild disease in humans

B. melitensis – Infects goats and sheep – Common in Malta, Med countries, Mexico, Middle East, South America – Causes severe disease in humans

Brucellosis B. suis – Infects pigs in USA, South America and Southeast Asia. – Causes severe disease with destructive lesions in humans

B. canis – Infects dogs – Uncommon cause of mild disease

Brucellosis Human brucellosis (Undulant fever or Malta fever) Bacteria enter through body abrasions, GIT and most commonly RT Infections more common in farmers, veterinarians and abattoir workers Unpasteurized cows’ milk (UK, USA) and goats’ milk and cheese (Mediterranean and Middle Eastern countries)

Brucellosis Pyrexia of unknown origin - PUO No person-to-person spread Infection is common worldwide Incidence is low in the developed countries

Pathogenesis Bacteria  regional lymph nodes  thoracic duct  blood = Septicemic phase Reticuloendothelial cells are then infected Bacteria survive for a long time Inflammatory (granulomatous) reaction with epitheliod and giant cells, central necrosis and peripheral fibrosis

Pathogenesis Infection is subclinical Incubation period 1-3 weeks Gradual onset of malaise, fever, drenching sweats, aching and weakness A rising and falling (undulant) fever in minority of patients Enlarged lymph nodes and spleen Bone marrow lesions can progress to osteomyelitis and cholecystitis, endocarditis and meningitis

Chronic Brucellosis Patients gradually recover Chronic stage – more than one year Tiredness, aches and pains with anxiety, depression and occasional fever Relapses and remission may occur The organism cannot be isolated at this stage Difficult to diagnose Agglutinating titres are generally high.

Diagnosis Blood culture Bone marrow or lymph nodes biopsy Urine culture Serology – IgM present in acute brucellosis – IgG and IgA in chronic cases – A rising titre suggests infection

Treatment and Prevention Tetracycline + Streptomycin Rifampicin + Doxycycline – For 2 – 3 months

Prevention – Pasteurization of milk and milk products – Protective clothing and goggles – No satisfactory available vaccine – Animal vaccine with A19 strains

Case presentation A 50-year farmer who keeps goats and sheep on his farm as a source of providing milk for his family, came down with fever (To = 39.6oC), drenching sweats, joint pains and headache of 2 weeks duration What is your working diagnosis? How would you investigate this case? Which infecting organisms do you have in mind? What is the treatment of choice? How can this infection be prevented and controlled?