bubble_chart Overview

Endemic typhus, also known as murine typhus, is an acute infectious disease transmitted by rat fleas. Its clinical features are similar to those of epidemic typhus, but the condition is milder, the course of the disease is shorter, and the rash is rarely hemorrhagic.

bubble_chart Epidemiology

Local-type macula and papule cold-damage disease is sporadically distributed worldwide, predominantly in tropical and subtropical regions, and is classified as a natural focal disease. The disease occurs more frequently in late summer and during the autumn grain harvest, and it can coexist with the epidemic-type macula and papule cold-damage disease in certain areas. In China, more cases have been reported in Henan, Hebei, Yunnan, Shandong, Beijing, and Liaoning, with multiple studies documented between 1982 and 1984.

(1) Source of pestilence: Domestic rodents such as brown rats and yellow-breasted rats serve as the primary source of pestilence for this disease, circulating in a cycle of rat→rat flea→rat. Most infected rats do not die, and rat fleas only bite humans and transmit the infection after the rats die. Since Rickettsia mooseri has been isolated from lice, patients may also act as a source of pestilence and spread the disease.

(2) Transmission route: When rat fleas suck the blood of infected rats, the pathogen enters the flea's gut and multiplies, but the flea does not die from the infection, and the pathogen can persist in the flea for a long time. When an infected flea bites a human, it simultaneously excretes flea feces and vomiting matter containing the pathogen onto the skin, allowing the rickettsiae to enter the body through scratches or broken skin. Alternatively, if the flea is crushed, the pathogen inside its body can invade through the same route. Consuming food or drink contaminated by the excreta of infected rats can also lead to infection. The pathogen in dried flea feces may occasionally form aerosols, infecting humans through the respiratory tract or conjunctiva. Arthropods such as mites and ticks may also carry the pathogen and potentially act as vectors.

(3) Susceptible population: Humans are generally susceptible to this disease, with some reports indicating higher incidence among elementary school students and young adults. After infection, individuals develop strong and lasting immunity, which also provides considerable protection against Rickettsia prowazekii infection.

bubble_chart Pathogen

The pathogen is Rickettsia mooseri, whose morphology, staining, and resistance to heat and disinfectants are similar to those of Rickettsia prowazekii, but it rarely forms long chains. Each contains three-fourths of specific granular antigens and one-fourth of group-specific soluble antigens; the latter are heat-resistant and shared by both, thus capable of inducing cross-reactions. The heat-labile granular antigens, however, are specific to each and can be differentiated by complement fixation tests. The scrotal reaction in guinea pigs caused by Rickettsia mooseri is far more pronounced than that caused by Rickettsia prowazekii, and its pathogenic nature in mice and rats is also stronger. Inoculation of the pathogen into the peritoneal cavity of mice can cause peritonitis, rickettsemia, and the presence of the pathogen in various organs.

bubble_chart Pathogenesis

The condition is generally similar to epidemic maculopapular cold-damage disease, but vascular lesions are milder, and thrombosis in small blood vessels is less common.

bubble_chart Clinical Manifestations

The incubation period is 8 to 14 days, with most cases being 11 to 12 days. The clinical symptoms are similar to those of epidemic macula and papule cold-damage disease, but central nervous system symptoms are milder, and petechial rashes are rare.

Most cases have an abrupt onset, while a few may experience 1 to 2 days of prodromal symptoms such as fatigue, poor appetite, headache, etc. The fever is continuous or remittent, peaking in the first week of the illness, generally around 39°C, accompanied by generalized body aches, severe headache, conjunctival congestion, etc. Some cases may experience arthralgia, which affects mobility, and the headache is often caused by retro-orbital pain. The fever typically lasts 9 to 14 days and mostly subsides gradually.

Approximately 50–80% of patients develop a rash, most commonly between the 4th and 7th day of illness. It initially appears on the chest and abdomen, spreading within 24 hours to the back, shoulders, arms, legs, etc., while the face, neck, soles, and palms usually remain unaffected. The rash begins as macula and papule, pink in color, 1–4 mm in diameter, and blanches upon pressure; it then progresses to maculopapular lesions, dark red in color, which do not blanch immediately. The rash fades within a few days. In very rare cases, the rash may be hemorrhagic.

Central nervous system symptoms, apart from headache, dizziness, insomnia, hearing impairment, and dysphoria, include occasional signs of meningeal irritation, delirium, unconsciousness, and urinary incontinence. Cough is present in more than half of the cases, with occasional rales heard at the lung bases, and some patients complain of sore throat and chest pain. Constipation is common, while nausea, vomiting, and abdominal pain are also observed. Jaundice has a higher incidence in certain series but is generally grade I; splenomegaly occurs in more than half of the cases, while hepatomegaly is less common. Myocardial involvement is rare, though bradycardia may occasionally occur. The most common complication is bronchitis, with occasional cases of bronchopneumonia. Other complications include renal failure.

bubble_chart Auxiliary Examination

In the early stage of the disease (within 7 days), grade I leukopenia and thrombocytopenia occur in 1/4 to 1/2 of cases. Subsequently, nearly one-third of patients exhibit an increase in total leukocyte count. Prothrombin time may be prolonged, but disseminated intravascular coagulation (DIC) is rare. In 90% of patients, serum aspartate aminotransferase shows grade I elevation, and ALT, AKP, and LDH levels are also frequently elevated. Other abnormalities include hypoalbuminemia (45%), hyponatremia (60%), and hypocalcemia (79%). Severe cases may present with elevated serum creatinine and blood urea nitrogen.

Patient serum may also agglutinate with Proteus OX₁₉ strains, with titers ranging from 1:160 to 1:640, which is lower than that seen in epidemic macula and papule cold-damage disease. Positive reactions appear between the 5th and 17th day of illness, averaging between the 11th and 15th day. Although the Weil-Felix test is sensitive, its specificity is poor and cannot be used to differentiate it from epidemic macula and papule cold-damage disease. More sensitive and specific tests include indirect immunofluorescence antibody detection, latex agglutination test, complement fixation test, and solid-phase immunoassay, using specific Rickettsia mooseri antigens. The indirect fluorescent antibody titer rises in 50% of cases within the first week of illness and in nearly 100% within 15 days. Facilities with the necessary resources may use PCR to detect Rickettsia mooseri-specific nucleic acid in blood samples.

General laboratories should avoid performing guinea pig scrotal reaction tests to prevent the spread of infection among animals and potential exposure of laboratory personnel.

bubble_chart Diagnosis

The diagnosis is primarily based on epidemiological data, fever duration, the nature of the rash, and the Weil-Felix test. When conditions permit, additional serological tests such as complement fixation tests and rickettsial agglutination tests can be performed, excluding epidemic maculopapular cold-damage disease.

bubble_chart Treatment Measures

It is essentially the same as the epidemic type of macula and papule cold-damage disease. A domestic series (1985) reported 186 cases, with 101 cases treated with doxycycline 200mg administered at draught, and 85 cases treated with tetracycline 2g daily (divided into four doses), for a course of 5–7 days. The results showed that fever subsided within 2 days in 77% of the doxycycline group and 26% of the tetracycline group, with a significant difference between the two (P < 0.05). The recurrence rate was 3.9% in the doxycycline group and 2.4% in the tetracycline group. Some domestic experts also suggest that antibiotics may not be necessary for other cases except for those diagnosed early or with complications, where doxycycline may be added.

bubble_chart Prognosis

Good, with timely treatment such as doxycycline and chloramphenicol, deaths are rare.

bubble_chart Prevention

Start with rodent and flea eradication, see Section 36 "Plague." Vaccination follows the epidemic type of macula and papule cold-damage disease, targeting rodent control workers and laboratory personnel exposed to Rickettsia mooseri.

bubble_chart Differentiation

This disease also needs to be differentiated from cold-damage disease, influenza, scrub typhus, leptospirosis, and others.