Rickettsial infection among military personnel deployed in Northern Sri Lanka
Premaratna et al. BMC Infectious Diseases
Rickettsial infection among military personnel deployed in Northern Sri Lanka
Ranjan Premaratna 0
Nimalka Ariyaratna 2
Champaka Attanayake 1
Wijesinghe Bandara 4
Nilmini Chandrasena 3
H Janaka de Silva 0
0 Departments of Medicine, Faculty of Medicine, University of Kelaniya , Ragama , Sri Lanka
1 Military Hospital , Palali , Sri Lanka
2 Military Hospital , Colombo , Sri Lanka
3 Department of Parasitology, Faculty of Medicine, University of Kelaniya , Ragama , Sri Lanka
4 Department of Microbiology, Faculty of Medicine, University of Kelaniya , Ragama , Sri Lanka
Background: Military personnel deployed in field actvities report on frequent tick bites. Therefore they may run the risk of exposure to rickettsial organisms. Methods: In order to assess the risk of exposure to rickettsial organisms, two groups of military personnel who were deployed in field activities of Nothern Sri Lanka were investigated. The first group was studied in order to assess the sero-prevalence of rickettsioses and consisted of soldiers who were admitted following injuries during field activities. The second group was studied to identify the incidence of acute rickettsioses during their acute febrile presentations. They were tested with IFA-IgG against spotted fever group rickettsioses (SFG), scrub typhus (ST) and murine typhus. Results: In the first group, 48/57 (84%) military personnel had serological evidence of exposure to rickettsioses (in all, IFA-IgG titer 1:128): 33/50 (66%) to SFG rickettsioses, 1/50 (2%) to ST and 14/50 (28%) had mixed titers for both (in all, titers were higher for SFG). While all of them were in military uniform most of the time and frequently slept on scrub land, 35/57 (61.4%) had never used insect repellents and none were on doxycycline prophylaxis. 48/57 (84%) had experienced tick bites during field activity. In the second group, there were 49 who presented with acute febrile illness with a mean duration of 8.5 days (SD 3.2). 33/49 (67.3%) were serologically positive for acute rickettsioses (IgG 1:256); 26 (79%) due to ST and 7 (21%) due to SFG rickettsioses, Conclusions: Exposure to rickettsial disease was common among soldiers who were deployed in Northern Sri Lanka. Scrub typhus was the predominent species accounting for acute febrile illness. Further studies are needed to understand the reasons for very high sero-prevalence for SFG rickettsioses with no anticedent febrile illness. Use of preventive measures was not satisfactory. The high sero-prevelence of SFG rickettsioses is likely to interfere with serological diagnosis of acute SFG rickettsioses in this population.
Rickattsial infections; Military; Sri Lanka
Rickettsial infections are re-emerging in Sri Lanka [1,2].
The history of rickettsioses dates back to the world wars
when the troops arriving in Sri Lanka, then Ceylon, were
attacked by chigger mites resulting in severe scrub
typhus infection. The diagnosis of the illness had been
based on the presence of eschars and high OXK titres
. Among the military most scrub typhus patients had
presented with febrile illness. However some patients
have had serious complications such as encephalitis,
pneumonitis and deafness . Recent literature from the
country document re-emergence of spotted fever group
rickettsioses (SFG), typhus fever and scrub typhus (ST)
[1,2,4]. These infections are prevalent in almost all the
parts of the island, however spotted fever group
rickettsioses seems to predominate in the hilly central region
and scrub typhus in the dry and wet lands of low
country [1,2,4]. Although most SFG infections are sporadic
and occur throughout the year, scrub typhus seems to
have a seasonal occurrence .
The main vectors for scrub typhus (caused by O.
tsutsugamushi) are chigger mites, and for SFG rickettsioses
are tick species. Military personnel who are actively
engaged in field activities complain of frequent tick bites
and therefore may run the risk of developing rickettsial
infections. We present the outcome of two study groups
that were done in 2008 in order to understand the
occurrence of rickettsioses among military personnel who
were deployed in Northern Sri Lanka.
For the group one military personnel who were admitted
to the Colombo North Teaching Hospital, Ragama, for
management of injuries during field activities in early
2008 were recruited. The sero-prevalence rate for
rickettsioses in the country is largely unknown however 56.3%
mean sero-prevalence has been documented for four
geographical regions . As military includes individuals from
many geographical regions within the country, their back
ground sero-prevalence may vary. However since their
activities expose them for insect and tick bites, we presumed
that they may have had a higher risk for rickettsioses than
the general population. We recruited a convenient sample
for this preliminary study. After obtaining informed
consent, they were interviewed by three experienced medical
officers using a pre tested questionnaire. The
questionnaire included data on demography, their service period
in the area, activities they were engaged in, leasure
activities, clothing, exposure to insects and ticks and its
frequency, use of insect repellents and the frequency and
history of febrile illness during the service period.
They were tested for serological evidence of
rickettsioses using 1 ml serum sample collected for other
The group two consisted of 49 consecutive admissions to
Palali Military Hospital, Northern Sri Lanka, who
developed an acute febrile illness during field activities. The
study was carried out over a period of four months
commencing from August 2008. They were tested for
rickettsioses as part of investigation for febrile illness.
Serum samples were transported in ice to the Rickettsial
Disease Diagnostic and Research Laboratory, Faculty of
Medicine, University of Kelaniya for rickettsial antibody
testing using Immuno Fluorescent Antibody (IFA) test
against SFG rickettsioses and ST, using R. conorii, R. typhi
and O tsutsugamushi antigens. In the first study, exposure
to a rickettsial agent was defined when they had a
IFAIgG titre 1:64. In the second study the presumptive
diagnosis of acute rickettsioses was based on the presence of
acute febrile illness that is compatible with acute
rickettsioses together with rapid deferversence with
antirickettsial antibiotics and an IgG titre of 1:256  and when
they were negative for other causative aetiology for acute
febrile illness [based on blood picture for malaria, blood
culture for bacterial growth, serology for leptospirosis and
Ethical approval for both studies were obtained from
the Ethics Review committee of the Faculty of Medicine,
University of Kelaniya, Sri Lanka. Informed written
consent was obtained from all participants of group one and
informed verbal consent was obtained from the
participants of group two in order to use demographic,
clinical and serological data without reveling their personal
Results and discussion
The group one included 57 military personnel (all males)
with a mean age of 25.8 (SD 5.5) years and a mean period
of 6.7 (SD 5) years of active service in operational areas.
They were from 20 out of 25 districts of Sri Lanka,
however all 57 had served in the Northern Province and 13
had served in the Eastern Province of Sri Lanka in
addition. 24/57 (42%) had a history of febrile illness during
their service period (four were confirmed as malaria and
the rest were undiagnosed). Although all of them were in
military uniform most of the time, they had frequently
slept on scrub land. 35/57 (61.4%) had never used insect
repellents and the rest had used them infrequently. None
of them were on doxycycline prophylaxis. 48/57 (84%)
had experienced tick bites during field activities. 48/57
(84%) had serological evidence of exposure to rickettsioses
(in all the, IFA-IgG titer was 1:128); SFG rickettsioses in
33/50 (66%), ST in 1/57 and for both SFG and ST in 14/
57 (28%) (all 14 had higher titres for SFG) and none for R.
During the four month period, all 49 patients (all males)
who presented with acute febrile illness and admitted to
the Palali Military hospital were recruited. Their mean age
was 28.66 (SD: 7.5) years and duration of fever was
8.5 days (SD 3.2). Of the 49, 33 (67.3%) were serologically
positive for acute rickettsioses (in all of them the IgG
dilution titre was > 1:1024). 26/49 (53%) were due to ST and
7/49 (14%) were due to SFG rickettsioses. All responded
well to doxycycline or doxycycline and azithromycin in
combination. Among the study participants, 32/49 (65%)
had 1:128 IFA-IgG titres for SFG rickettsioses. None of
them were positive for R. typhi. Out of the 26 patients
who had ST, 10 had been sleeping in a single field camp
for two nights during field activity and all of them were
admitted within a space of two weeks from the first
patient. None of these patients had used insect repellents
or doxycycline prophylaxis. Out of the patients with
rickettsioses, 12/33(36%) had eschars, 20/33 had
pneumonitis (Diagnosed by clinical and radiological features)
and 6 of them had reduced capillary oxygen saturation
(<93%) on air. 8 patients had myocarditis (Diagnosed by
ECG changes and by ECHO cardiography) and one
patient had meningo-encephalitis (Diagnosed by clinical
features and EEG. This patient had an eschar suggesting the
aetiological diagnosis of rickettsioses. Therefore lumbar
puncture was not attempted). Two patients who had
multiple organ involvement and needed intensive care
management. Of the 16 non-rickettsial patients, 4 had vivax
malaria, 6 had undetermined upper respiratory tract
illness, 5 had leptospirosis and one had salmonella infection.
In the group one, 84% showed evidence of exposure to
SFG rickettsioses (transmitted by hard ticks) compared
to ST (transmitted by mites). These military personnel
were originally from either wet or dry zones of low
country in Sri Lanka. In the group two, 79% had high
titres for ST and 21% had high titres for SFG rickettsioses.
All of them had clinical response with anti-rickettsial
antibiotics confirming the diagnosis of acute rickettsioses.
The two military groups had been in uniforms during
most of the time, they had been sleeping in scrub land
and they had not been taking precautions against insect
The outcome of group two suggested risk of the military
mainly for ST outbreaks similar to that was observed
during World Wars. As this study was carried out over a
period of only 4 months and the sample consisted of
several soldiers who were deployed in the same locality the
predominant species that is responsible for acute
rickettsioses in operational areas cannot be confirmed. However
soldiers are known to run the risk of acquiring ST
infection when they come in contact with mite islands.
We observed 84% sero-prevalence for rickettsioses in
the group one. A 56.3% mean seroprevalence rate for
rickettsioses has been documented in a previous community
study conducted in four geographical regions of the
country . In that study, the IgG cutoff titre had been 1:64.
However we observed 1:128 IgG titres among the first
study group. The reasons for high titres against SFG
rickettsioses in this group could not be assertained with the
currently available diagnostic facilities. However, the study
populations had no documented febrile illness during
their service period. Therefore, one possibility for this
observation could be repeated exposure to non-pathogenic
rickettsial species resulting in development of nonspecific
cross reacting antibody titres in them . Similar
observations were made among workers of a wild life
conservation park of Sri Lanka, who had many tick bites almost
daily for several years, and had almost 100%
seroprevelence for SFG rickettsioses, but had no evidence of
febrile illness (unpublished data). If our assumption would
be a likely possibility, it is important to study and identify
such rickettsial agents that are harboured by wild ticks
because some of the rickettsial organisms initially thought to
be non-pathogenic have later being identified as
pathogenic . Rickettsial sero-prevalence among populations
is known to be determined by their occupations, activities
involved or climatic conditions. A 57.3% sero-prevalence
for SFG rickettsioses has been documented among rubber
estate workers in Slim River, Malaysia during wet season
in December 1996 . Screening of 169 US Army troops
who participated in a 10 day training course in Botswana
in 1999 has reported overall sero conversion rate of 14%
(24/169) for SFG rickettsioses . During the period the
second study, the area had mostly a dry weather until mid
September. There were two weeks of heavy rains during
the latter part of September and in early October and the
area remaind fairly wet for the next two months.
These soldiers had minimal understanding on rickettsial
diseases and its mode of transmission. They had been in
military uniforms and were sleeping in the scrub land as
they were engaged in active militory efforts. They had not
been carring any sleeping material with them during the
Exposure to rickettsial disease is common among soldiers
who are deployed in Nothern Sri Lanka. The high
seroprevalence for SFG rickettsioses with no anticedent febrile
illness warrent a closer look most appropriately by
studying the offending ticks in order to assertain the rickettsial
species that are carried by them. As exposure to rickettsial
infections are high among the military, preventive
measures such as use of insect repellents and doxycycline
prophylaxis should be strongly recomended for them. The
higher background IgG antibody titres against SFG
rickettsiosdes is likely to interfere with serological diagnosis of
acute SFG rickettsioses among these populations.
RP: designed the study, writing up the paper. NA, CA: management of cases,
design the study. TGANC, NKBKRGWB: analysis of samples, writing up the
paper. HJdeS: design the study, writing up the paper. All authors read and
approved the final manuscript.
We thanks Medical officers of the Professorial Medical Unit, Dr. Nawasiwatte
BMTP., Dr. Kulasiri KIR., Dr. Rajeev S and the staff of Military hospital, Palali
Jaffna for the assistance given during the study.
1. Kularatne SA , Edirisingha JS , Gawarammana IB , Urakami H , Chenchittikul M , Kaiho I : Emerging rickettsial infections in Sri Lanka: the pattern in the hilly Central Province . Trop Med Int Health 2003 , 8 : 803 - 811 .
2. Liyanapathirana VC , Thevanesam V : Seroepidemiology of rickettsioses in Sri Lanka: a patient based study . BMC Infect Dis 2011 , 11 : 328 .
3. Noad KB , Haymaker W : The neurological features of tsutsugamushi fever, with special reference to deafness . Brain 1953 , 76 : 113 - 115 .
4. Premaratna R , Loftis AD , Chandrasena TGAN , Dasch GA , de Silva HJ : Rickettsial infections and their clinical presentations in the western province of Sri Lanka: a hospital based study . Int J Infect Dis 2008 , 12 : 198 - 202 .
5. Nanayakkara DM , Kularatne SAM , Wickramasinghe WMRS , Budagoda BDSS , Weerakoon KGAD , Dasch DA , Rajapakse RPVJ : Seroprevalence of Rickettsioses Among Human Population of Sri Lanka: A Study in Four Regions . Sri Lanka: Proceedings of Peradeniya Univ Research Sessions ; 2009 : 14 .
6. Premaratna R , Weerasinghe S , Ranaweera A , Chandrasena TG , Bandara NW , Dasch GA , de Silva HJ : Clinically helpful rickettsial disease diagnostic IgG titers in relation to duration of illness in an endemic setting in Sri Lanka . BMC Res Notes 2012 , 5 : 662 .
7. Raoult D , Roux V : Rickettsioses as paradigms of new or emerging infectious diseases . Clin Microbiol Rev 1997 , 10 : 694 - 719 .
8. Parola P , Paddock CD , Raoult D : Tick-borne rickettsioses around the world: emerging diseases challenging old concepts . Clin Microbiol Rev 2005 , 18 : 719 - 756 .
9. Tee TS , Kamalanathan M , Suan KA , Chun SS , Ming HT , Yasin RM , Devi S : Seroepidemiologic survey of Orientia tsutsugamushi, Rickettsia typhi, and TT118 spotted fever group rickettsiae in rubber estate workers in Malaysia . Am J Trop Med Hyg 1999 , 61 : 73 - 77 .
10. Smoak BL , McClain JB , Brundage JF , Broadhurst L , Kelly DJ , Dasch GA , Miller RN : An outbreak of spotted fever rickettsiosis in U.S. Army troops deployed to Botswana . Emerg Infect Dis 1996 , 2 : 217 - 221 .