Brucella

Brucellosis (undulant fever) is a zoonosis Members of the genus Brucella are primarily pathogens of animals Different species of Brucella are each associated with particular animal species B. ovis are known to cause disease in humans

General characteristics The brucellae are aerobic, facultative, intracellular parasites that can survive and multiply within host phagocytes. unencapsulated Small coccobacilli arranged singly or in pairs Lipopolysaccharide is the major virulence factor, as well as the major cell wall antigen.

Epidemiology Brucellosis is a chronic, lifelong infection in animals. Organisms localize in reproductive organs (male and female), shed in large numbers in milk, urine, and the placenta and tissues discharged during delivery or spontaneous abortion. primary manifestations of infection in animals are sterility and abortion. Transmission to humans via :  direct contact with infected animal tissue  ingestion of unpasteurized milk or milk products

Pathogenesis Brucellae enter the body through  cuts and abrasions in the skin  the gastrointestinal (GI) tract.  Inhalation of infected aerosols Once the organisms gain entry, -transported via the lymphatic system to the regional lymph nodes, where they multiply. -carried by the blood to organs that are involved in the reticuloendothelial system, including the liver, spleen, kidneys, bone marrow, and other lymph nodes

Clinical significance The incubation period ranges from five days to several months, but typically lasts several weeks. Symptoms are nonspecific,flu-like and GI symptoms, and may also include depression. Their onset may be abrupt or insidious. Untreated, patients may develop an undulating pattern of fever Subclinical infections occur. Brucellosis may involve GI tract, skeletal, neurologic, cardiovascular, and pulmonary systems.

Laboratory identification history is often crucial The organism can be cultured from blood and other body fluids or from tissue specimens. Multiple blood specimens should be cultured., colonies may appear in four to five days; cultures, examined for up to one month before being declared negative

Treatment Combination therapy involving doxycycline and gentamicin (or streptomycin) is recommended for brucellosis Prolonged treatment (for example, six weeks) is necessary to prevent relapse and reduce the incidence of complications.

Bordetella Bordetella pertussis and B. parapertussis are the human pathogens of this genus. Bordetella pertussis causes the disease pertussis (whooping cough) Whooping cough is a highly contagious disease and a significant cause of morbidity and mortality worldwide. ‌

General characteristics Members of the genus Bordetella are aerobic and Small encapsulated,coccobacilli that grow singly or in pairs. serotyped on the basis of cell-surface molecules

Epidemiology The major mode of transmission of Bordetella is via droplets spread by coughing The incidence of whooping cough among different age-groups vary, depending on active immunization of young children. In the absence of an immunization program, disease is common among young children (ages one to five).

Pathogenesis B. pertussis binds to ciliated epithelium in the upper respiratory tract There, the bacteria produce a variety of toxins and other virulence factors that interfere with ciliary activity, eventually causing death of these cells

Clinical significance The incubation period for pertussis ranges from 1-3weeks The disease can be divided into two phases:  catarrhal  paroxysmal  Catarrhal phase: -Runny nose -malaise, -mild fever.

Clinical significance(cont’d)  Paroxysmal phase: - Coughing - vomiting. - Leukocytosis convalescence requires at least an additional three to four weeks. Disease is generally most severe in infants

Treatment and prevention Erythromycin is the drug of choice for infections with B. pertussis For erythromycin treatment failures, trimethoprim-sulfamethoxazole is an alternative choice. Prevention -Pertussis vaccine is available that has had a significant effect on lowering the incidence of whooping cough

Legionella Legionellaceae are facultative intracellular parasites cause primarily respiratory tract infections Unencapsulated, relatively slender rods,Coccobacillary Aerobic fastidious, with a particular requirement for L- cysteine

Epidemiology The Legionellaceae family includes 34 species normal habitat is soil and water 85 to 90% of human disease is caused by a single species, Legionella pneumophila. Most infections result from inhalation occasionally from swimming in contaminated water. organism is chlorine tolerant.

Pathogenesis The organism enter the upper respiratory tract by aspiration of water containing the organism Inhalation of a contaminated aerosol. when reached the lungs. Alveolar macrophages in the lung do phagocytose L. pneumophila, the organisms multiply within phagosome until the cell ruptures, releasing a new crop of bacteria

Clinical significance Legionellaceae primarily cause respiratory tract infections. There are two distinctly different presentations:  Legionnaires' disease  Pontiac fever.

Clinical significance(cont’d) Legionnaires' disease (LD): This is an atypical, acute lobar pneumonia with multisystem symptoms. Legionellae are estimated to cause 1-5%of the cases of community-acquired pneumonias in adults fatality rate for LD ranges from 5-30% Symptoms develop after 2-10 days. Early symptoms nonspecific: fever, malaise, myalgia, anorexia, and/or headache. Cough, Diarrhea (watery rather than bloody stools) Nausea, vomiting, and neurologic symptoms may also occur

Pontiac fever This is an influenza-like illness The attack rate among those exposed to a common source is typically 90% or more. Recovery is usually complete within one week. No specific therapy is required.

Laboratory identification the organism can be Gram stained, the Gimenez stain is more useful for visualization. culturing of Legionella from respiratory secretions, using buffered (pH 6.9) charcoal yeast extract enriched with L-cysteine, iron, and ketoglutarate. Visible colonies form in three to five days. A urinary antigen test using an enzyme immunoassay is available and has several advantages over culture..

Treatment Macrolides, such as erythromycin or azithromycin, are the drugs of choice for Legionnaires disease. Fluoroquinolones are also effective Pontiac fever is usually treated symptomatically, without antibiotics.

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