Historical backgroundCharacteristics of legionellaVirulence factorsPathogenesisClinical manifestationsDiagnostic laboratory testsImmunity against legionellaNormal habitat & Epidemiology Transmission and controlTreatmentSummary references

CONTENTS

Historical backgroundCharacteristics of legionellaVirulence factorsPathogenesisClinical manifestationsDiagnostic laboratory testsImmunity against legionellaNormal habitat &

Epidemiology Transmission and controlTreatmentSummary references

CONTENTS

Historical Background and Epidemiology

Historical Background The name legionella originates

from a widely publicized outbreak of pneumonia in persons attending an American Legion convention in Philadelphia in 1976.

In a hotel on the occasion of a United States army veterans’ meeting (Fraser et al., 1977).

Legionellaceae are facultative intracellular parasites that cause primarily respiratory tract infections.

Legionella are :• gram-negative • slender rods• unencapsulated• fastidious, • Aerobic • catalase-positive• Most produce gelatinase and ß-lactamase• 0.5–1 m wide and 2–50 m long.• poorly stained by Gram's stainThis has been attributed to the presence of the branched chain

fatty acids that are a major component of the cell walls.

Bacterial Characteristics

• Motile by means of one or more polar or subpolar flagella• grown on complex media such as buffered charcoal-yeast

extract (BCYE) agar with ; ketoglutarate, pH of 6.9, temperature 35 °C, and 90% humidity.• Legionellae grow slowly; 3 days of incubation with BCYE & ≥2 weeks in blood cultures • Colonies are round or flat, colorless to iridescent pink or blue

Virulence factorsThe Legionellae make:• proteases,• phosphatase, • lipase, • DNase, and • Rnase• A major secretory protein,

a metalloprotease, has hemolytic and cytotoxic activity; however, this protein has not been shown to be a required virulence factor.

PathogenesisLegionellae are intracellular pathogens of macrophages, by

which they are phagocytosed in a process involving ;

1. Both virulent and non-virulent strains are phagocytosed

2. Virulent strains can multiply inside the phagocytes and

are able to inhibit the fusion of phagosomes with

lysosomes

non-virulent strains do not multiply

3. The bacteria multiply within the vacuoles until they are

numerous,

4. The cells are destroyed, the bacteria are released, and

infection of other macrophages then occurs. (transferrin-iron) is essential for the process of intracellular

growth of the bacteria, but other factors important to the processes of growth, cell destruction, and tissue damage are not well understood.

Clinical FindingsLegionellaceae primarily cause respiratory tract infections. There are two distinctly different presentations:

1. Legionnaires' disease and2. Pontiac feverAsymptomatic infection is common in all age groups. in which,The

incidence of clinically significant disease is highest in men over age 55 years.

Factors associated with high risk include:• smoking, • chronic bronchitis and emphysema, • steroid and other immunosuppressive treatment (as in renal

transplantation)• cancer chemotherapy, and • diabetes mellitus. When pneumonia occurs in patients with these risk factors, legionella

should be investigated as the cause.

• L.neumophilia causes Legionnaires' disease can have symptoms like many other forms of pneumonia, so it can be hard to diagnose at first.

Signs of Legionnaires' disease can include:CoughShortness of breathHigh feverMuscle achesHeadaches

These symptoms usually begin 2 to 14 days after being exposed to the bacteria.

Clinical manifestations

• Chest x-rays reveal patchy, often multilobar consolidation.

• There may be leukocytosis, hyponatremia, hematuria (and even renal failure), or abnormal liver function.

Potanic fever• L .pneumophila also produces a disease called "Pontiac fever," after the

clinical syndrome that occurred in an outbreak in Michigan. characteristics fever and chills, myalgia, malaise, and headache ,that develop over 6–12 hours. Dizziness, photophobia, neck

stiffness, and confusion also occur.• The symptoms of Pontiac fever are similar to those of Legionnaires’ disease

and usually last for 2 to 5 days. Pontiac fever is different from Legionnaires' disease because the patient does not have pneumonia.

• Symptoms go away on their own without treatment.

SpecimensThe organisms can be recovered from:• bronchial washings • pleural fluid• lung biopsy specimens or• blood Isolation of legionella from sputum is more difficult because

of the predominance of bacteria of the normal flora. Legionella is rarely recovered from other anatomic sites.

Smears Legionellae are not demonstrable in Gram-stain Direct fluorescent antibody tests, but the test has low

sensitivity compared with culture Silver stains are sometimes used on tissue specimens.Culture Specimens are cultured on BCYE agar & can be rapidly

identified by immunofluorescence staining. BCYE agar containing antibiotics can be used

DIAGNOSTIC LABORATORY TESTS

Specific Tests The urine antigen test is specific for L. pneumophila serotype 1.Serologic Tests Levels of antibodies to legionellae rise slowly during the illness. Serologic tests have :

a sensitivity of 60–80% anda specificity of 95–99%. Serologic tests are most useful in obtaining a retrospective diagnosis in outbreaks of legionella infections.

• Infected patients make antibodies against legionella but the peak antibody response may not occur until 4–8 weeks after infection.

• The roles of antibodies and cell-mediated responses in protective immunity in humans have not been defined.

• The host defense against Legionella relies principally on cell-mediated immune mechanisms.

• One protein produced by L. pneumophila, the major secretory protein (MSP, 39kDa), is able to

• induce protective cell-mediated immunity without being a virulence factor (Blander & Horowitz,1991).

No vaccine has so far been tested in humans!!!

IMMUNITY

Legionellae are ubiquitous in warm moist environments

Legionellae grow best in warm water in the presence of amebas and water bacteria.

The Legionellaceae family includes 34 species & many of them lives in; soil and water, cooling towersevaporative condenserswater distribution systems

85 to 90 % of human disease is caused by a single species, Legionella pneumophila.

Normal habitat & epidemiology

Hot tubs Cooling towers Hot water tanks Large plumbing

systems Decorative fountains

Epidemiology L .pneumophila is responsible for

approximately 1% to 3% of community-acquired pneumonias, 13% of those acquired in the hospital

• It is estimated that about 25,000 to 100,000 Legionella infections occur annually

• The resulting mortality rate, which ranges up to 40% in untreated immunocompetent patients

• L. pneumophila is estimated to be responsible for 80% to 85% of reported cases of Legionella infections

Transmission and Control Transmission

Control• Hyperchlorina

tion and superheating of water can help control the multiplication of Legionellae in water and in air-conditioning systems.

• Legionellae are susceptible to erythromycin and some other drugs. The treatment of choice is erythromycin, which has been effective even in immunocompromised patients.

• Rifampin, 10–20 mg/kg/d, has been used in patients whose response to treatment was delayed.

• Assisted ventilation may be necessary, and management of shock is essential.

Treatment

Legionnaires' disease is the more severe form and can be fatal.

Pontiac fever is the far milder form of the illness.

Symptoms of Legionnaires' disease include fever, chills, and a cough. At its worst, Legionnaires' disease can cause severe pneumonia and respiratory failure.

Summary

references ’’ Jawetz, Melnick, & Adelberg's Medical Microbiology, 24th

Edition by Vishal : Lippincott’s microbiology

Addis DG et al. (1989). Community acquired Legionnaires’ disease associated with a cooling

tower: evidence for longer distance transport of Legionella pneumophila. American Journal of Epidemiology, 130:557–568.

Adeleke A et al. (1996).

End of discussion!!! relax..!!!!