**5. Scrub typhus**

The etiological agent of scrub typhus is *Orientia tsutsugamushi,* which is transmitted by chigger bites (trombiculid mite larvae). It is mainly distributed in Afghanistan, India, Pakistan, Sri-Lanka, Kashmir, China, Nepal, Japan, Korea, Vietnam, Indonesia, Laos, Philippines, Papua New Guinea and Australia (Figure 11). Cases are mainly observed in autumn and spring, in temperate zones where the bite of this arthropod, which is on vegetation, is frequent. The incubation period is about 10 or more days and the clinical signs and symptoms are similar to typhus syndrome, including the rash which is transient and easily missed. A difference with typhus syndrome is the presence of eschar that is frequently multiple. The presence of regional lymphadenopathy is also more frequent. The mortality can be high despite the correct antimicrobial treatment. Outbreaks related to military operations have been reported (Pages et al., 2010). Most travel acquired cases of scrub typhus occur in patients returning from Southeast Asia (Jensenius et al., 2004, 2006).

Rickettsiosis as Threat for the Traveller 17

Ticks removed from patients can be used as tools for the diagnosis of tick-borne rickettsioses. The strategy includes the identification of the tick to the species level, and the

2. Detection of bacteria in ticks with the use of staining tests (haemolymph for viable ticks; salivary glands if ticks were frozen), or PCR-based methods (using one-half of the tick, the other half being kept frozen). PCR may also be done using only ticks that

3. Sequencing of the amplified PCR fragment and comparison with available sequences

4. If there is 100% similarity between the tested sequence and the corresponding sequence

5. If the tested sequence appears to be different from all corresponding sequences available, the organism is probably a new strain and should be isolated and

Diagnostic scores with epidemiological, clinical and laboratory tests for some tick-borne

b. Clinical and epidemiological features highly suggestive of ATBF, such as multiple inoculation eschars and or regional lymphadenitis and or a vesicular rash and or similar symptoms among other members of the same group of travellers coming back

c. Clinical and epidemiological features consistent with a spotted fever group rickettsiosis such as fever and or any cutaneous rash and or single inoculation eschar

Serology specific for a recent *R. africae* infection (seroconversion or presence of IgM ‡ 1:32), with antibodies to *R. africae* greater than those to *R. conorii* by at least two dilutions, and or a Western blot or cross-absorption showing antibodies specific for *R.* 

Table 4. Diagnostic criteria for African-tick bite fever (ATBF). A patient is considered to have

of a known organism, the presumptive identification is confirmed

characterized from the stored frozen part of the tick

Table 3. Strategy for detecting and/or isolating rickettsias from ticks

rickettsioses (ATBF and MSF) have been proposed (Tables 4 and 5).

a. Direct evidence of *R. africae* infection by culture and or PCR

Positive serology against spotted fever group rickettsiae

after travel to sub-Saharan Africa or French West Indies

from an endemic area (sub-Saharan Africa or French West Indies)

detection or isolation of rickettsias (Table 3).

stain positive.

*or* 

*and* 

*or* 

*and* 

*africae*

ATBF when criteria A, B or C are met

in sequence databases.

1. Identification of the ticks to the species level
