Rickettsia Start before friday

Rickettsia

A group of bacteria and related organisms that commonly use arthropods as vectors and cause diseases such as typhus and spotted fevers

Rickettsiaceae

The bacterial family associated with Rickettsia

Howard Ricketts

Pathologist who identified the causative agent of Rocky Mountain Spotted Fever and studied its cultivation and epidemiology

Common characteristics of Rickettsia

Small pleomorphic Gram negative rods that are difficult to stain and usually require living cells for growth

Obligate intracellular parasite

An organism that requires living host cells for growth

Rickettsial stains

Gimenez stain, Giemsa stain, and Macchiavello stain

Rickettsial culture

Growth in embryonic eggs, tissue culture, or laboratory animals

Rickettsial laboratory safety

Suspected cultures require specially equipped facilities because of the risk of laboratory acquired infection

Initial diagnosis of rickettsial disease

Based on clinical presentation, patient history, and symptoms; treatment should not wait for laboratory confirmation

Fastest confirmation method in the lecture

Fluorescent antibody testing for microbial antigen in a skin punch biopsy

PCR for Rickettsia

A molecular method available for detecting rickettsial organisms

Serologic diagnosis

Detection of patient antibodies that react with specific microbial antigens

Weil Felix test

A serologic agglutination test that detects patient antibodies cross reactive with somatic O antigens of certain nonmotile Proteus strains

Weil Felix OX19

Proteus vulgaris strain used in the Weil Felix test

Weil Felix OX2

Proteus vulgaris strain used in the Weil Felix test

Weil Felix OXK

Proteus mirabilis strain used in the Weil Felix test

Principle of the Weil Felix test

Antigenic cross reactivity occurs between Rickettsia and certain Proteus strains

Weil Felix test limitation

Proteus infections can produce positive results, and some rickettsial diseases do not produce reliable antibody titers

Weil Felix test advantage

Inexpensive, rapid, widely available, and may provide early diagnostic clues

Pathogenesis of Rickettsia

Organisms attack the reticuloendothelial system and multiply in endothelial cells lining blood vessels

Rickettsial vasculitis

Inflammation of blood vessels caused by rickettsial infection

Cause of rickettsial rash

Damage and inflammation of blood vessel endothelial cells

Common rickettsial symptoms

Fever, rash, and headache

Usual treatment for rickettsial infections

Tetracycline or doxycycline; the lecture identifies doxycycline as the recommended treatment for Rocky Mountain Spotted Fever, ehrlichiosis, and anaplasmosis

Rickettsial prevention

Reduce exposure to ticks, fleas, lice, and mites; control fleas on pets and keep rodents and other reservoirs away from living and recreational areas

Epidemic typhus agent

Rickettsia prowazekii

Epidemic typhus reservoir and vector

Humans are the reservoir and the body louse is the vector

Epidemic typhus transmission

An infected louse defecates near the bite; scratching introduces infectious material into the skin

Epidemic typhus incubation period

10 to 14 days

Epidemic typhus rash

Appears about 4 to 7 days after illness begins, starting on the trunk and spreading to the extremities; palms, soles, and face are usually spared

Epidemic typhus complications

Mental changes, kidney damage, gangrene, and potentially death

Epidemic typhus mortality

10 to 40 percent in untreated cases according to the lecture

Epidemic typhus prevention

Eradication of body lice with insecticides

Endemic typhus agent

Rickettsia typhi

Endemic typhus reservoir and vector

Rats are the reservoir and rat fleas are the vectors

Endemic typhus transmission

Infected flea feces contaminate the bite area and scratching introduces the organism into the skin

Endemic typhus presentation

Similar to epidemic typhus but generally milder; illness may last up to two weeks

Endemic typhus diagnosis

Weil Felix agglutination and complement fixation tests are listed in the lecture

Rocky Mountain Spotted Fever agent

Rickettsia rickettsii

Rocky Mountain Spotted Fever reservoir and vector

Rodents and dogs are listed as reservoirs; transmission occurs through tick bites

Rocky Mountain Spotted Fever vectors

Brown dog tick and Rocky Mountain wood tick

Rocky Mountain Spotted Fever incubation period

3 to 12 days

Rocky Mountain Spotted Fever rash

Appears about 2 to 4 days after illness begins, starting at the ankles and wrists and spreading; palms and soles may be involved

Rocky Mountain Spotted Fever symptoms

Abrupt fever, malaise, severe headache, and sometimes gastrointestinal symptoms, weakness, and conjunctivitis

Rocky Mountain Spotted Fever complications

Electrolyte changes, tissue necrosis, shock, and death

Rocky Mountain Spotted Fever mortality

About 3 to 6 percent with treatment and 20 percent without treatment according to the lecture

Rocky Mountain Spotted Fever treatment

Start doxycycline at the first indication of disease, especially when tick exposure is suspected

Rickettsial pox agent

Rickettsia akari

Rickettsial pox reservoir and vector

House mouse and mouse mite

Rickettsial pox presentation

Usually mild, with fever, headache, malaise, and rash; may be mistaken for chickenpox