Indian tick typhus is usually wrongly diagnosed as Rocky Mountain Spotted Fever (RMSF) due to its similarity with RMSF. In 1925 Megaw identified it as distinct entity. Before that it used to be diagnosed as RMSF.
The causative agent is Rickettsia conorii, which is a member of spotted fever group of rickettsiae. The tick is the reservoir of infection. Transmission of tick to tick is through transplacental mode. Incubation period is 3-7 days.
The mode of transmission: Man is only accidental host. Man acquires infection by tick bite. Contamination of skin by crashed tick can also be a mode of transmission. The transmission cycle is as follows:
Tick —–Tick ——- Tick —–Tick
Signs and symptoms: The patient generally gives history of tick bite and if examined carefully a lesion or eschar is seen at the site of the bite. After 3-7 days (incubation period) there is acute onset of fever (which may be for 2 to 3 weeks), headache and malaise. On the third day a maculopapular rash may appear. But unlike rashes of other rickettsial diseases the rash appear in the extremities like wrists and ankles first and them spreads it to the rest of the body.
Treatment: Broad spectrum antibiotics like tetracycline, doxycycline and chloramphenicol are the drug of choice for the treatment of Indian tick typhus.
Scrub typhus is the commonest type of typhus in men. Scrub typhus is caused by O. tsutsugamushi. It is maintained by transovarian transmission in trombiculid mites. After hatching, infected larval mites known as chigger, which is the only stage that feeds on a host, inoculate organisms into the skin. Scrub typhus is endemic in eastern and southern Asia, northern Australia, and islands of the western Pacific and Indian Oceans.
The mode of transmission is as follows:
Mite to Rats & mice to Mite to Rats & mice
Signs & Symptoms: The symptoms can be from mild self limiting disease to fatal. Incubation period of scrub typhus is 6–21 days. Fever, headache, cough, myalgia, and gastrointestinal symptoms are common. The classic symptom includes an eschar where the chigger feeds, regional lymphadenopathy, and a maculopapular rash, but only rarely seen. Severe cases include encephalitis and interstitial pneumonia which are due to vascular injury. The case-fatality rate for untreated classic cases is 7%.
Diagnosis: Diagnosis is mainly by clinical symptoms. IFA (immuno fluorescent assay), indirect immunoperoxidase, and enzyme immunoassays are the laboratory diagnosis techniques.
Treatment: Doxycycline 100 mg twice a day for 7 -15 days or chloramphenicol 500 mg four times a day orally for 7–15 days is the treatment of choice.
Some cases of scrub typhus as seen in Thailand are caused by doxycycline or chloramphenicol resistant strains. These doxycycline or chloramphenicol resistant cases of scrub typhus are treated with rifampin, azithromycin or clarithromycin.
Prevention: Good personal hygiene is required for prevention. Clearing of vegetation where rats and mice live and application of insecticides like lindane, chlordane to ground and vegetation to control the mite. No vaccine is available at present.
Epidemic or louse borne typhus is transmitted by Rickettsia prowazekii. The infection is transmitted from man to man by infected louse (Pediculus corporis, P. capitis). Lice acquire R. prowazekii when they ingest blood from a rickettsemic patient. Pediculus corporis lives in clothing under poor hygienic conditions and usually in impoverished cold areas. The rickettsiae multiply in the midgut of the louse and are shed in the louse’s feces. The infected louse leaves a febrile patient and deposits infected feces on its new host during its blood meal and the new host autoinoculates the organisms by scratching.
Epidemic or louse borne typhus can cause devastating outbreaks during war and disasters. In humans the organism can persist for many years with out any symptoms and the disease can manifest itself as Brill-Zinsser disease and can be transmitted by louse to other humans.
Signs & Symptoms: Incubation period is about 1 week. Onset of illness is abrupt, with severe headache and fever. Fever rises rapidly to 38.8°–40.0°C (102°–104°F). Cough is prominent (70% of patients get). Myalgia (muscle pain) if present is severe. There is characteristic “crouching” posture. Rash can be seen on the upper trunk, on the fifth day, and then becomes generalized and involve the entire body except the face, palms, and soles. But more than half of the patients do not develop rash. Photophobia, dry, brown, and furred tongue, skin necrosis and gangrene of the digits, confusion and coma are other symptoms.
Fatality is 7–40% in untreated cases.
Diagnosis: Epidemic or louse borne typhus is sometimes misdiagnosed as typhoid fever in tropical countries. It can be diagnosed by the serologic or immunohistochemical diagnosis of a single case or by detection of R. prowazekii in a louse found on a patient.
Treatment: Doxycycline (200 mg/d, given in two divided doses) is the treatment of choice. If there is vomiting or patient is unconscious doxycycline can be given intravenously. Treatment is continued for 2-3 days after symptoms subside, though single 200 mg doxycycline is sufficient.
During pregnancy chloramphenicol early in pregnancy or, if necessary, doxycycline late in pregnancy is the treatment of choice.
Prevention: The best way to prevent is to maintain good personal hygiene. Clothes should be washed and changed regularly. Insecticides can be used every 6 weeks to control the louse population.
Endemic murine typhus is caused by Rickettsia typhi. R. typhi is maintained in mammalian host-flea cycles, with rats (Rattus rattus and R. norvegicus) and the Oriental rat flea (Xenopsylla cheopis). Fleas get R. typhi from rickettsemic rats and carry the organism throughout their life. Humans are infected when rickettsia-laden flea feces contaminate itchy bite lesions. Rats are infected if they are not immune to R. typhi. The flea bite can also transmit the organisms, but much less frequently. Transmission can occur via inhalation of aerosolized rickettsiae from flea feces. Rats are rickettsemic for about 2 weeks, though they appear healthy.
Epidemiology: endemic typhus occurs year-round, in warm (often coastal) areas throughout the tropics and subtropics, where it is highly prevalent. In USA Murine typhus occurs mainly in southern Texas and southern California. The classic rat-flea cycle is absent and an opossum-cat flea (C. felis) cycle is prominent in USA.
Symptoms & signs: The incubation period typhus is 8–16 days. Headache, arthralgia, myalgia, nausea, and malaise develop 1–3 days before onset of chills and fever. Nausea and vomiting is very common. The duration of untreated illness ranges from 9–18 days. Rash is present in some patients in axilla or the inner surface of the arm.
About one third of the patients have respiratory problems like a hacking, nonproductive cough, pulmonary edema, and pleural effusions. Abdominal pain, confusion, stupor, seizures, ataxia, coma, and jaundice can be seen less frequently.
Diagnosis: Diagnosis is mainly by clinical symptoms. Cultivation and PCR in acute and convalescent-phase sera can provide a specific diagnosis of endemic murine typhus.
Treatment: Doxycycline 100 mg twice orally for 7–15 days on the basis of clinical suspicion is the treatment of choice.
Mediterranean Spotted Fever also known as Boutonneuse Fever. It is caused by Rickettsia conorii. It is prevalent in southern Europe, Africa, and southwestern and south-central Asia. Regional names for the disease caused by this organism include Mediterranean spotted fever, Indian tick typhus, Israeli spotted fever, Kenya tick typhus, and Astrakhan spotted fever.
The symptoms include headache, fever, eschar(tache noire), and regional lymphadenopathy. It is characterized by high fever, rash, and an inoculation eschar at the site of the tick bite. In patients with diabetes, alcoholism, or heart failure the disease can be very severe and mortality is as high as 50% in these patients.
Mediterranean Spotted Fever is diagnosed mainly by clinical findings in the areas where it is endemic and is confirmed by serology, immunohistochemical demonstration of rickettsia in skin biopsy and cell culture & isolation of rickettsia.
Treatment: The drug of choice for the treatment of Mediterranean Spotted Fever is doxycycline and ciprofloxacin. Doxycycline is given 100 mg orally two times a day for 1-5 days depending on severity. Ciprofloxacin is given 750 mg orally two times a day for 5 days. Other drug which can be used is chloramphenicol 500 mg orally four times per day for 7-10 days.
In mildly ill children clarithromycin or azithromycin can be used successfully. But these are not very successful for treatment of adults. These two drugs are also not useful in severely ill pediatric patients.
Rocky Mountain Spotted Fever (RMSF) is the most severe of all rickettsial diseases. RMSF is caused by Rickettsia Rickettsii. It is characterized by fever, headache, malaise, myalgia (muscle pain), nausea, vomiting, and anorexia for first three days. The patient becomes progressively ill.
RMSFoccurs in all 48 adjoining states in USA (highest prevalence in the south-central and southeastern states) and also in Canada, Mexico, and Central and South America. The infection is transmitted by Dermacentor andersoni, the Rocky Mountain wood tick, in the western United States and by D. variabilis, the American dog tick, in the eastern two-thirds of the United States and California. It is transmitted by Rhipicephalus sanguineus in Mexico and by Amblyomma cajennense in Central and South America.
Humans usually become infected during tick season (from May to September in the Northern Hemisphere).
Treatment: The drug of choice for the treatment of both adults and children with RMSF is doxycycline except when the patient is allergic to this drug or pregnant. Rocky Mountain Spotted Fever Is very severe disease and prompt treatment with empirical administration of doxycycline should be given as soon as it is diagnosed or suspected strongly. Doxycycline is administered orally at 200 mg/d in two divided doses, in the presence of coma or vomiting, it is given intravenously. For children, up to five courses of doxycycline may be administered with minimal risk of dental staining.
Other drugs include oral tetracycline (25–50 mg/kg per day) in four divided doses. Chloramphenicol can be given if patients are pregnant or allergic to doxycycline.
The antirickettsial drug should be given till the patient has been afebrile (without fever) and improving clinically for 2–3 days. ?-Lactam antibiotics like penicillin, erythromycin, and aminoglycosides have no role in the treatment of RMSF, and sulfa-containing drugs can aggravate this infection.
Prevention of RMSF: tick bites should be avoided as much as possible (although it is not very practicable). Protective clothing and tick repellents can be used; inspection of the body once or twice a day, and removal of ticks before they inoculate rickettsiae reduce the risk of infection. There is no vaccine available for RMSF.