Rickettsia vascular necrosis bacteria

2021-08-17 10:28 PM

Rickettsia shape changes through development stages: cocci stand-alone or in pairs, bacilli, and filaments. The most common are bacilli. Size 0.5x1µm.

Rickettsia was discovered by Ricketts and Wilder in 1910. Rickettsia was once considered closely related to viruses because of its small size and intracellular growth. Today Rickettsia is confirmed as a bacterium because:

Rickettsia has all the structural features of bacteria, especially having a typical cell wall.

Contains all the necessary enzymes for metabolism.

Contains both types of nucleic acids: DNA and RNA.

Bacterial cell division.

Oxygen use and sensitivity to certain antibiotics (chloramphenicol, tetracycline).

Rickettsial diseases have the following common features:

+ The source of transmission is the sporophyte insect, Rickettsia usually does not cause disease in insects but causes disease in humans.

+ Except for Q fever, the blood of patients with Rickettsia disease contains antibodies agglutinating with strains of OX19 or OXK of Proteus vulgaris.

+ Pathological lesions are mainly vasculitis except in Q fever pneumonitis is more important.

+ All diseases caused by Rickettsia are acute diseases with clinical symptoms: fever, headache, rash except Q fever without rash.

Based on clinical, epidemiological, and immunological characteristics, Rickettsia is divided into 4 groups:

+ Group I: Epidemic typhus, pathogens are: R. prowazeki, R. mooseri.

+ Group II: Nodular fever, pathogens are R. conori, R.rickettsi, R.canada, R.akari, R.australis.

+ Group III: Forest typhus group (Japanese river fever): R.tsutsugamushi (R.orientalis) is now Oriental tsutsugamushi

+ Group IV: Fever group “Q” (Query). The pathogen is: R. burnetti.

Biological characteristics

Shape

Rickettsia shape changes through development stages: cocci stand-alone or in pairs, bacilli and filaments. The most common are bacilli. Size 0.5x1µm. Gram staining is Gram-negative. On Giemsa or Machiavello staining, Rickettsia can be observed under an optical microscope. The Giemsa stain of bacteria catches blue, and the stain of Machiavello catches the red bacteria quite contrasting with the green color of the host cells.

Chemical structure

Rickettsia contains RNA and DNA in a ratio of 3.5:1, the cell wall resembles the cell wall of Gram-negative bacteria containing a glycopeptide complex.

Antigen structure

Two types of antigens are distinguished.

Soluble antigens have group specificity.

Insoluble antigens: related to the surface of bacteria, differentiated species.

Toxin

Some Rickettsia produces a culture-soluble toxin with hemolytic and necrotic properties. When this toxin is injected into animals, they die after a few hours and the pathological damage is similar to that caused by bacteria. In addition, the pathogenic activity also depends on the hemolytic enzyme, the toxin is tightly bound to the bacterial body. The toxin is destroyed at 60°C for 30 minutes but retains its antigenic properties. The toxin is neutralized by specific antisera.

Possibility to cause disease

Rickettsia develops in vascular wall endothelial cells, where they multiply and secrete procoagulant factor, mediated by a toxin that causes these cells to swell and then die, so the blood vessel is blocked. ruptured so lesions of blood vessels are visible in the skin.

In the brain, lesions in the blood vessels of the gray matter were found. Heart showing lesions in small blood vessels.

Microbiological diagnosis

Infusion into laboratory animals

Take blood at the onset of the disease and inject it into guinea pigs, mice or scrambled eggs. For Japanese river fever, specimens were injected into the peritoneum of mice, excreta of the rat peritoneum was spread on Giemsa stained slides, immunofluorescence staining.

Serum reaction

Non-specific reaction: Weil-Felix reaction:

Rickettsia and Proteus Vulgaris seem to share some antigens, when infected with Rickettsia, the patient produces some antibodies that agglutinate with some Proteus Vulgaris strains (OX19, OX2, OXK strains) such as R.prowazeki (OX19), Oriental tsutsugamushi (OXK), and R.mooseri (OX19).

Specific reactions:

Antigens harvested from bloodstock cultures can induce agglutination, complement incorporation, or immunofluorescence.

Prevention and treatment

Prevent

Rickettsia disease is transmitted by insects such as ticks, lice, lice, mites, etc., so it is necessary to kill the disease-transmitting insects. Prevention with vaccines for people going to the outbreak. The vaccine is prepared by antigens harvested from egg yolk sacs. It can also be prevented with antibiotics.

Treatment

Rickettsia is sensitive to antibiotics. Preferably treated with tetracyclines and chloramphenicol. Antibiotics inhibit the growth of Rickettsia. Sulfamides should not be used because they promote bacterial growth.

Important rickettsial diseases

Common in many places is typhus, rat typhus, Japanese river fever, and Q fever.

Epidemic typhus fever

Because R.prowazeki is an acute disease transmitted by lice. Characteristics: high fever, persistent headache, rash, lethargy, lethargy. The temperature can be up to 39 - 40oC in the first day or 2-3 days later, when the temperature is up to 40oC, it will stay the same, with little change until healing or treatment. A persistent, severe headache that is difficult to improve with all efforts to relieve the pain. The rash occurs from day 4 to day 7, initially on the upper body and then spreading all over the body except the face, palms, and feet. Conjunctivitis and facial flushing were also observed. If treated well, the temperature returns to normal within 2-5 days. Recovery time takes 2-3 months. In outbreaks, the mortality can be from 6 to 30%. The disease is associated with war and poverty.

Mouse typhus fever

Caused by R. Mosseri, in nature is an infectious disease of mice caused by the flea Xenopsylla cheopis which transmits the disease from mice to humans. The disease is found in many parts of the world, especially in ports. Acute febrile illness has featured in common with epidemiological typhus but is milder, rarely fatal, except in elderly and frail patients. The disease develops gradually, the fever is rarely 39oC, usually goes up and down and stops after 9-13 days, the headache is less severe, the rash is less strong, the rash time is shorter.

Japanese River Fever

By Oriental tsutsugamushi. Acute febrile illness, which can be mild or severe, is transmitted from rodents to humans. The disease usually comes on suddenly, with fever, chills, headache, ulcerated and black scaly stings, enlarged adjacent lymph nodes, and conjunctivitis often observed. Fever can go up to 40.5 C and stay at that level for 14 days or more. In untreated patients, headache is severe and persistent. You appear in the body from the 5th to the 8th day. In addition, in critically ill patients who are not treated, there are signs of pneumonia, central nervous system signs: delirium. The severity of the disease varies by region.

Q fever (Query)

The agent is R.burneti. The source of the disease is ticking which is transmitted to livestock. The disease is transmitted from cattle to humans mainly by inhalation of contaminated dust, without rash, without agglutinating antibodies to Proteus Vulgaris. The disease is endemic in many parts of the world. The illness usually comes on suddenly: fever, headache, fatigue, flu-like illness, atypical pneumonia. Severe headache is a fairly specific feature, with temperature fluctuations, and usually lasts 6-12 days. Respiratory signs: X-ray film shows clustered infiltrates similar to atypical pneumonia. The disease usually heals without leaving any sequelae.