Rickettsia spotted fever is a group of clinically similar diseases caused by rickettsia, including rocky mountain spotted fever, Mediterranean spotted fever, African tick bite fever, Queensland tick typhus, and North Asia tick fever. These diseases are mainly transmitted by hard ticks and are widely found all over the world.
Rocky mountain spotted fever
Rocky mountain spotted fever, also known as North American tick typhus, new world spotted fever, tick-borne typhus fever, and Sao Paulo fever, is an acute endemic infectious disease caused by rickettsia rickettsii transmitted by ticks.
Sources of infection
Sources of infection are animals such as rabbits, squirrels, deer, and bears infected with rickettsia rickettsii, and hard ticks serving as reservoir hosts and transmission vectors.
Modes of transmission
Rickettsia rickettsii maintains circulation in certain ticks and animals. When entering the epidemic area, humans can be infected by tick bites. In addition, if humans are exposed to crushed ticks or tick feces, rickettsia can enter the human body through the breached skin or conjunctiva, and humans can also be infected by contaminated blood transfusion or inhalation of contaminated aerosols in laboratories.
Humans are generally susceptible, and lasting immunity can be acquired after infection.
Signs and Symptoms
The incubation period is 2 - 14 days, averagely 7 days. The shorter the incubation period is, the more severe the condition is. After the incubation period, some patients may have 1 - 3 days of prodromal symptoms, manifested by anorexia, fatigue, limb weakness, and chills.
Sudden onset and rapid body temperature rise, up to 39 - 40 ℃ in typical patients and up to 41 ℃ in severe patients, are present. Symptoms are chills, severe headaches, generalized muscle and joint pain, photophobia, and postocular pain. Hepatolienomegaly may occur. If untreated, fever does not regress, persisting for 2 - 3 weeks. Eventually, fever slowly drops in most patients.
Differences from other spotted fever are absent ulcers or eschars (primary sores) at the tick bite sites. If a bacterial infection occurs at the bite site, there may be purulent inflammation or pustules.
Skin lesions occur in 80% - 90% of patients 3 - 4 days after onset of fever, initially on the wrists and ankles, extending to the arms, feet, chest, abdomen, and maxillofacial region. Skin lesions are pale red spots with a diameter of 2 - 5 mm, which fuse and turn red or purple 2 - 3 days after eruption. The skin lesions gradually subside during the recovery period, progressing into petechiae at the folded skin of the palms, soles, ankles, and armpits. After the skin lesions subside, there may be transient pigmentation and branny desquamation.
In patients who have not been effectively treated, rickettsia can severely damage the vascular endothelium, causing thrombosis and ischemic gangrene, mostly on the nasal tip, earlobes, scrotum, and digits. If aortic thrombosis occurs, necrosis of extremities and hemiplegia can occur. Severe patients often die from myocarditis and pulmonary edema.
If patients have a history of exposure to ticks within 2 weeks before onset, and clinical manifestations, such as acute fever, severe headaches, photophobia, postocular pain, and pale red spots on wrists and ankles, are present, the disease should be highly suspected. Positive Weil-Felix reaction and immunological results are conducive to clinical diagnosis.
Chloramphenicol and tetracyclines have specific effects on this disease. Due to adverse effects in clinical practices, chloramphenicol is no longer preferred. Doxycycline is used more frequently, with simple administration, few side effects, and satisfactory results. Erythromycin, fluoroquinolones such as norfloxacin, enoxacin, and ciprofloxacin, and minocycline can also be selected.
If no effective pathogen treatment is performed, the mortality rate can reach 20% - 30%. After prompt and effective treatment, the mortality rate can reduce to 3%. The pathological changes in fulminant patients present irreversible progressive development, and patients may die within 3 - 5 days.
Rats and ticks should be eliminated.
Mediterranean spotted fever
Mediterranean spotted fever, also known as Boutonneuse fever, Mediterranean tick fever, Marseilles fever, Kenya tick typhus, India tick typhus, and Israeli tick typhus, is a mild or severe febrile illness caused by rickettsia conorii transmitted by ticks on dogs and rodents.
Epidemiology is the same as those of rocky mountain spotted fever.
Signs and Symptoms
The incubation period is 5 - 7 days.
Sudden high fever, chills, headaches, tiredness, arthralgia, and stomachache are present. Fever lasts for 7 - 14 days. A hard papule occurs at the tick bite site during fever, and then turns black, forming an ulcer of 2 - 5 mm in diameter due to central necrosis, with red halos, enlarged lymph nodes, and tenderness. Reddish maculopapular rashes occur 3 - 4 days after onset, probably hemorrhagic in severe patients, initially in the forearm, spreading to the whole body soon, including the face, palms, and soles. Skin lesions gradually subside after fever reduces. A good prognosis is present, and complications are less common.
Diagnosis, treatment, and prevention are the same of those of rocky mountain spotted fever.
Queensland tick typhus
Queensland tick typhus is caused by rickettsia australis transmitted by ticks.
Symptoms and signs are the same as those of Mediterranean spotted fever, and blisters may be present.
Epidemiology, diagnosis, treatment, and prevention are the same as those of Mediterranean spotted fever.
North Asia tick fever
North Asia tick fever, also known as Siberian tick typhus, is caused by rickettsia sibirica transmitted by ticks.
Symptoms and signs, epidemiology, diagnosis, treatment, and prevention are the same as those of Mediterranean spotted fever.