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MindMap Gallery Infectious Diseases - Rickettsiosis - Scrub Typhus

Infectious Diseases - Rickettsiosis - Scrub Typhus

Mind map of university clinical medicine major - "Infectious Diseases" 06. Rickettsiosis - scrub typhus, produced according to teaching PPT and corresponding textbook (Blue Paper "Infectious Diseases 9th Edition") during classroom learning, including etiology, epidemiology, diagnosis and treatment, differential diagnosis, prognosis and prevention etc., detailed content. It can be used for students in related majors to study and take exams, or for friends who are interested in medicine to understand and refer to. Due to different teaching syllabuses, some content in the textbook has not been produced. Friends who need it can leave a message in the comment area, and updates will be added later. Maps of other courses in the major can be viewed on the homepage after following it. Comments and corrections are welcome. Like, collect and follow to get more information and not get lost. Update record: 2023.10.21-Publish works, paid clones

Edited at 2023-10-21 21:01:23

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Infectious Diseases - Rickettsiosis - Scrub Typhus

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Outline

Rickettsiosis - scrub typhus

Overview

definition

Also known as scrub typhus, an acute natural foci infectious disease caused by Orientia scrub typhus

Named after the bites of chiggers, the main source of infection in rodents

Clinical features

Burning or ulcer formation at the bite site, fever, rash, lymphadenopathy, hepatosplenomegaly, and leukopenia in peripheral blood, etc.

Etiology - Orientia scrub typhus

Structure and composition

They are spherical or club-shaped, obligate intracellular parasitism, and are arranged in piles near the nucleus in the cytoplasm.

Gram stain is negative, Giemsa stain is purple-blue

survival and reproduction

Reproduction by binary fission, chicken embryo yolk sac, mouse intraperitoneal inoculation and isolation

Cross-immunogenicity with Proteus OXK

Weak resistance

Has natural deactivation and cracking tendency, making it difficult to preserve

Very sensitive to general disinfectants, sensitive to chloramphenicol, tetracycline, and erythromycin

Able to withstand cold and tolerate penicillins, cephalosporins and aminoglycoside antibiotics

Epidemiology

Source of infection

Rats are the main source of infection

In the south, Rattus rattus and Rattus norvegicus are the dominant species, in towns and cities in Guangdong, house rats are dominant, and in rural areas, Rattus rattus and Rattus norvegicus are the dominant species.

In the north, the main species are the black-lined rat and the social rat.

Rabbits, pigs, poultry, birds, chiggers, etc.

People (patients) are of little significance as a source of infection

After a person suffers from this disease, although Orientia scrub typhus is present in the blood, the possibility of being bitten by chigger larvae is extremely small.

way for spreading

Chiggers—transmission vector and original reservoir host

There are dozens of chiggers that can transmit this disease. The most important ones in my country are Chiggers spp. and Chiggers red.

life cycle

There are 5 stages of eggs, larvae, pupae, larvae and adults. Only the larvae are parasitic.

Propagation mode

Bites of pathogen-carrying chigger larvae

population susceptibility

Generally susceptible, with many exposure opportunities and higher incidence rate

Long-lasting immunity to the same pathogen can be acquired after illness

Immunity against different strains only lasts for a few months, so infection can occur again

popular features

Mainly prevalent in the Asia-Pacific region, especially in Southeast Asia

Generally distributed, can also be popular

There are seasonal differences in epidemics between north and south of my country

More in the south than in summer and autumn

The peak period from June to August is related to the spread of chiggers on the ground caused by concentrated rainfall.

More in the north than in autumn and winter

The peak in October is related to the increased density of chiggers and wild mice.

Pathogenesis

within local tissue cells

Reproduction, localized skin lesions

Enter blood via lymph

Scrub typhus Orientiaemia

Vascular endothelial cells and mononuclear phagocytes grow and multiply, producing toxins, causing systemic toxin symptoms and multiple organ lesions.

Pathological changes

Systemic small vessel vasculitis, perivasculitis and mononuclear phagocyte proliferation

local skin

Congestion and edema → small papules → small blisters, central necrosis and bleeding, forming a round black scab called eschar

Eschar falls off → ulcer, surrounding lymph nodes swell

viscera

The liver and spleen are congested and enlarged, and focal or diffuse myocarditis and hemorrhagic pneumonia may occur. Interstitial nephritis, lymphocytic meningitis, etc.

clinical manifestations

incubation period

4-21D, generally 10-14D

Week 1

fever

Generally there are no prodromal symptoms, the onset is sudden, reaching 39-41°C within 1-2 days, and the fever is flaccid, persistent or irregular, lasting 1-3 weeks.

With symptoms of systemic poisoning

Chills, severe headache, body aches, fatigue, drowsiness, loss of appetite, nausea, vomiting, etc.

physical signs

Flushing of face, neck and chest, conjunctival congestion, eschar or ulcer, swollen lymph nodes, rash, hepatosplenomegaly

Week 2

nervous system

Apathetic expression, hard of hearing, irritability, delirium, even convulsions and coma, etc.

circulatory system

Symptoms of myocarditis such as fast heart rate, irregular rhythm, and weak heart sounds

respiratory system

Symptoms of pneumonia such as cough, sputum production, and shortness of breath

A small number of extensive bleeding

Epistaxis, gastrointestinal bleeding

Critical cases show severe multi-organ damage, including heart, liver, kidney and circulatory failure, which may be complicated by DIC.

Week 3

The body temperature gradually drops to normal, the symptoms reduce to disappear, and the patient gradually recovers.

If the pathogen is not treated promptly and effectively, the patient may become seriously ill and die.

Characteristic signs

Eschar and ulcers

The most diagnostic significance, seen in more than 70% of patients

Round or oval, burnt black

Different sizes, mostly 4-10mm in diameter

The edge is slightly raised, like a dike, with a blush around it

No pain, no itching, no oozing

After the scab falls off, an ulcer forms in the central depression

Most patients have only one eschar

More common in moist and sweaty areas (armpits, external genitalia, groin, perineum, perianal area, lower back, etc.)

swollen lymph nodes

The local lymph nodes near the eschar are often significantly swollen (this can be used to look for eschar)

Different sizes, movable, accompanied by tenderness, no suppuration

Superficial lymph nodes throughout the body are often slightly swollen

rash

In a few cases, it appears immediately after the onset of the disease, and the symptoms may be mild or asymptomatic.

It usually appears within 4-6 days of the disease and lasts for 3-7 days before resolving.

Dark red congestive maculopapular rash, a few are hemorrhagic, not itchy or scaling, 2-5mm in diameter, does not fade when pressed

Distributed on the trunk and limbs, rarely on the face, and rarely on the palms and soles of the feet

Hepatosplenomegaly

Hepatomegaly accounts for 10% to 30%, and splenomegaly accounts for 30% to 50%. The texture is soft, the surface is smooth, and there may be slight tenderness.

laboratory tests

Blood

WBC is often reduced or normal, but may increase in severe patients. The classification often shows left-shifted neutrophil nuclei and a relative increase in lymphocytes.

serology test

Proteus OXk agglutination reaction (Waifei test)

It can be positive on the 4th day, and about 90% positive in the 3rd week, and then decreases

The specificity is low, and the titer ≥1:160 has diagnostic significance.

The serum titer increases by more than 4 times every other week, which has greater diagnostic significance.

Specific IgM or IgG antibodies

significance

IgM has early diagnostic value; both sensitivity and specificity are good

method

complement fixation test

Immunofluorescence test

dot immunoassay

Enzyme-linked immunosorbent assay (ELISA) and enzyme immunoassay (EIA)

Pathological examination

Pathogen isolation

Mouse and chicken embryo vaccination

Molecular Biology Examination

PCR detection of Orientia scrub typhus DNA

complication

Toxic hepatitis, bronchopneumonia, myocarditis, meningoencephalitis, gastrointestinal bleeding and acute renal failure, etc.

diagnosis

Epidemiological data

Within 3 weeks before the onset of illness, sitting or lying in the affected area, at work, or on the grass

clinical manifestations

Symptoms (acute onset, high fever, toxemia)

Signs (eschar or ulcers, lymphadenopathy, rash, hepatosplenomegaly)

laboratory tests

Decreased peripheral blood leukocyte count

Waifei-Fei test (Wai-Fei reaction agglutination titer ≥1:160 has auxiliary diagnostic value)

Serum specific antibody IgM has early diagnostic value

Isolate pathogens

PCR technology can detect Orientia scrub typhus DNA in cells and blood samples

Intraperitoneal inoculation of mice can culture and isolate pathogens

Differential diagnosis

leptospirosis

Often significant gastrocnemius pain

No rash, eschar or ulcers

White blood cell count often slightly increased

Specific leptospira agglutination test of serum

typhus

More common in winter and spring and cold areas

Have a history of lice or rat flea bites

No eschar

Wai-Fei test OX19 positive, OXk negative

Typhoid fever

Residual fever, bradypulse roseola on mask face, no eschar, hypertrophy test, culture

Influenza, malaria, sepsis, dengue fever, hemorrhagic fever with renal syndrome, etc.

prognosis

If early diagnosis and effective pathogen treatment can be carried out, the prognosis of most patients is good.

Death usually occurs after the third week of the disease, due to multiple organ failure, lung or gastrointestinal bleeding.

treat

General treatment

Rest in bed, eat easy-to-digest foods, strengthen nursing care, pay attention to oral hygiene, and turn over regularly

Symptomatic treatment

Physical cooling and calming

Pathogen treatment (reducing fever within 1 to 3 days)

Tetracycline family: doxycycline (with special effects)

The adult dose is 0.2g, once/d for 5 to 7 days. It has many adverse reactions in children and should be used with caution

Roxithromycin

Adults: 0.6 g/d, children: 2 to 3 mg/kg/d, 2 divided doses. After the fever subsides, the dose is reduced by half, and the course of treatment is 10 days.

Chloramphenicol

The dosage is 2g/d for adults and 25-40mg/kg/d for children. After the fever subsides, reduce the dose by half and use for another 7 to 10 days.

Penicillins, cephalosporins and aminoglycoside antibiotics have no therapeutic effect on this disease

prevention

Control sources of infection

Get rid of rats. Patients do not need to isolate, contacts do not need to quarantine

Cut off transmission routes

The key is to avoid chigger larval bites

Improve sanitary environment and eliminate chigger breeding areas

When working outdoors, you must tie up your sleeves and trousers tightly and apply insect repellent

Protect vulnerable groups

There is no vaccine yet, strengthen personal protection