Taurine Levels in Human Aqueous Humour

MEDICAL SCIENCES (2000), 2, 7−10
© 2000 SULTAN QABOOS UNIVERSITY

1Department of Microbiology and Immunology, Sultan Qaboos University, P.O.Box: 35, Postal Code: 123, Muscat, Sultanate of Oman;
2Department of Tropical Hygiene and Public Health and 3Department of Parasitology, University of Heidelberg, Im Neuenheimer, Feld 324, D –
69120 Heidelberg, Germany

*To whom correspondence should be addressed. 7

Antibodies against rickettsia in humans and
potential vector ticks from Dhofar, Oman

*Idris M A1,2 , Ruppel A2, Petney T3

لها والقراد الناقل للريكتسياتاألجسام المضادة
محافظة ظفارب
بتني. روبل ، ت. إدريس ، أ. م

تنتقل هذه الجرثوميات بواسطة أنواع مختلفة من المفصليات من بينها القراد مسببه أمراضًا مثل . واسعة أألنتشار تصيب أألنسان والحيوان عصيات بكتيرية الريكتسيات هي :الملخص
آل من مصر ، سوريا ، باآستان ، إثيوبيا لقد تم إآتشاف اإلصابة بهذه الجرثوميات في منطقة الشرق األدنى في . ، حمى جبال الروآي البقعاء والحمى القرادية ) التيفوس(الحمى البقعاء
عدوىلقد تم في هذه البحث مسح مصلى لألجسام المضادة. الريكتسيات بين األفراد في شبه الجزيرة العربية بما فيها سلطنة عمان عدوىحسب علمنا ال توجد معلومات عن . والصومال

محافظة -ومراجعي العـيادة الخارجية بمدينة الحق ومزارعين بصاللة ) ، طوى إعتير ، ضلكوت و رخيوت بسدح( مصال تم جمعها من تالميذ المدارس 347الريكتسيات بفحص
قرادة من 707أيضًا تم جمع ودراسة . الريكتسياتموجبة لألصابة ب من األمصال تحتوي أجسامًا % 59 البحث أن أثبتوقد تمت دراسة األجسام المضادة بطريقة التألق المناعي . ظفار
ــوانًا 102 ــز ( حي ــ ـار وماعـ ـال ، أبقـ ــفار ) جمـ ـافظة ظـ ــن محـ ــواع . مــ ــمي ألن ــ ــراد وجد أنه ينـت ـيف الق دارســة وتصـن الحلميا ت المتغيرة الشكل، والقراد الزجاجي العين بأنواعه وـب

.دل على إمكانية إنتشار اإلصابة بالريكتسيات بتلك المنطقةوجميع هذه األنواع من القراد يمكنها نقل العدوى مما ي. والقراد ذو الرأس المروحي

ABSTRACT: ���������
To determine the extent of rickettsial infections prevalence of potential vector ticks in the rural population of
Dhofar, Oman� ���
�� – Human sera (n = 347) were obtained from six rural localities (school children, farmers, outpatients) in Dhofar,
Sultanate of Oman. Sera were tested by immunofluorescence for the presence of antibodies reacting with Rickettsia conorii antigen. ������� –
More than half the samples (59%) gave positive reactions (titres of at least 1:64). Ticks (n=707) were collected from cattle, camels and goats
(n=102) and included Amblyomma variegatum, Hyalomma a. anatolicum, H. dromedarii, H. rufipes and Rhipicephalus spp., all of which can potentially
transmit rickettsiae to humans. ���������� – The results suggest that rickettsial infections are common among the rural population of
Dhofar.

KEY WORDS: Rickettsia, antibodies, immunofluorescence, vector ticks, cattle, camels, goats, Dhofar, Oman

ickettsial infections of man are widely
distributed.1 They cause several forms of dis-
ease including spotted fevers, which are

transmitted by ticks. In the near east, the presence of
spotted fever rickettsiae as pathogens of man is well
documented for Israel and Egypt2-5 and for Somali
refugees.6 However, no information is available for
much of the Arabian Peninsula, including the Sultanate
of Oman. The potential for the disease to occur in this
area is high as a variety of tick species, which can
transmit rickettsiae, has been recorded in Yemen7,
Saudi Arabia8 and Oman.9

The present study was carried out in order to
obtain an estimate of the prevalence of antibodies
against Rickettsia conorii in the Dhofar Province, which
covers the southern part of the Sultanate of Oman. A
detailed account of the environmental geography of
Dhofar region has been given by Sale.10 Except for the

regional capital Salalah, the population has a
predominantly rural lifestyle where people live in close
proximity to their animals. Ticks were therefore
collected from domestic stock in this region to
investigate the presence of potential vectors of spotted
fever rickettsiae.

METHOD

The study localities were illustrated by Idris11
except for Shab Al-Saeeb, Rakhyut, Tawiattair and
Sudh all within 30 to 160 km from Salalah, the capital
of Dhofar. Blood was collected from volunteer school
children (aged 8-16 years) in four localities in the
Dhofar Province (Sudh, Dhalqut, Tawiattair and
Rakhyut), from an outpatient clinic in Madinat Al-Haq
and from workers at the Royal Farm in Salalah.

Sera were transported frozen to Heidelberg where
they were tested by the indirect fluorescent antibody

I D R I S E T - A L

test (IFA) using Rickettsia conori-Spot IF (bioMérieux
Deutschland GmbH, Nürtingen, Germany). Princi-
pally, the serum is placed on a Rickettsia conori-Spot IF
antigen fixed slide. Antibodies fixed to this antigen are
revealed by a fluorescein labelled anti-human globulin.
A positive reaction is indicated by fluorescence of R.
conorii on the slide, visible under an ultravoilet (UV)
microscope.

Sera were diluted in two-fold series from 1:16 to 1:
256 and applied to the slides. These were incubated in
a moist chamber for 30 minutes at 37oC, washed twice
for five minutes each time in Tris (0.01M)-buffered
(pH 7.2) saline (PBS) with 0.05% Tween 20, dipped in
distilled water and drained. They were then incubated
as above in a moist chamber with fluorescein (FITC)-
conjugated goat antibodies against human IgG
(Behringwerke, Marburg, Germany) diluted 1:100 in
PBS with 0.01% Evans Blue. Slides were washed as
above and coverslips mounted with Fluoprep
(bioMérieux). The results were read in a fluorescence
microscope at ×400 magnification. According to the
manufacturer, only fluorescent reactions with patient
serum dilutions of at least 1:40 can be considered
positive. In this study, fluorescent reactions obtained at
dilutions of 1:64 or higher were taken as a positive
reading. Confirmatory determinations were done for
some random samples of sera and yielded identical
results.

Ticks were collected from livestock at Dhalqut,
Madinat Al-Haq, Tawiattair and Shab Al-Saeeb areas
through the cooperation from the animal’s owners and
veterinary practioners. In addition, the skins of freshly
slaughtered camels, cows and goats were searched for
ticks at Salalah municipality slaughter house, where
animals are brought from various localities in Dhofar.
Care was taken to obtain tick specimens from several
sites including the ears, groin and anal area. Ticks from
each animal were stored separate and preserved in
70% ethanol. Ticks were determined with respect to
species, development stage and sex.

RESULTS AND DISCUSSION

Table 1 shows that between 42% and 66% of hu-
man sera from each locality gave a positive reaction.
The results obtained from children were not detectably
different from those obtained from adults. The data
show that more than half (59%) of those individuals
tested had antibodies against R. conorii. This suggests
that rickettsial infections are common among the rural
population of Dhofar. The situation appears similar to
that in the Nile river delta of Egypt, where up to 96%,
81% and 37% of the school age children were found

seropositive for R. burnetii, R. typhi and R. conorii,
respectively.4

In order to search
conorii, the ticks, collec
camels and goats), wer
known ability to transm
total of 707 adult ticks
contribute to the natur
conorii on the following
use domestic stock as r
stages in their life histo
come into contact w
variegatum and Hyalomma
conorii;12,13 immature stag
and adults of H. rufipes
(iii) H. anatolicum ssp. is
and H. dromedarii was
specimens) infected wit
siae.5 Both H. anatolicum
humans.14

The genus Rhipiceph
of the main vectors of R
been confused with R.
attack humans, but the s
for R. conorii, is un
elucidated.16,17 Rickettsia
related to R. conorii, ha
turanicus.18 In addition to

Prevalence of antibodies

individuals from six

Population Loca

Sudh

Dhalq

Tawia
School children

Rakhy

Outpatients MadinHaq

Farm workers Salala

Total
TABLE 1.

against Rickettsia conorii among
localities in Dhofar, Oman

Rickettsia Conori-
Spot I.F

lity
No. of sera

tested
No. of sera

with positive
reaction*

64 31 (48)

ut 71 47 (66)

ttair 54 34 (63)

ut 67 41 (61)

at Al- 60 39 (65)

h 31 13 (42)
for potential vectors for R.
ted from 102 animals (cows,
e screened for species with a
it this pathogen (Table 2). A

were identified, which might
al epidemiological cycle of R.
basis: (i) All these tick species
egular hosts for one or more
ry and are, therefore, likely to
ith humans. (ii) Amblyomma
rufipes are known vectors of R.
es of A. variegatum frequently,

occasionally, attack humans.9,14
a known vector for R. conorii,
reported to be (one out of 70
h spotted fever group rickett-
ssp and H. dromedarii attack

alus includes R. sanguineus, one
. conorii. This species has often
turanicus which is known to
tatus of R. turanicus as a vector
certain15 and needs to be
massiliae, a species closely
s also been isolated from R.
R. turanicus, R.camicasi belongs

347 205 (59)

A N T I B O D I E S A G A I N S T R I C K E T T S I A

to the R. sanguineus group of species and both are
morphologically similar: it is difficult to distinguish
their males and their engorged females are almost
indistinguishable19 from each other. The involvement
of R. camicasi in disease epidemiology is unknown.16
Both R turanicus and R. camicasi are found in Oman.9
In view of the problems encountered in identifying
vectors of R. conorii in the R. sanguineus group, the
identification of Rhipicephalus to species level was not
attempted.

This report confirms the earlier records of tick
species in Oman by Hoogstraal.9 It amply demon-
strates the presence of ticks on domestic stock with the
potential to transmit spotted fever group rickettsiae to
humans. This, together with the rural life style of the
local population,20,21 is compatible with a high preva-
lence of seropositivity in humans. However, the fol-
lowing three points deserve further investigation:

First: whereas the serological data demonstrate a
substantial prevalence of rickettsial infections, the cut-
off titre set in immunofluorescence determines the
sensitivity and specificity of the results as was sug-
gested by comparative Western blotting performed
with specific protein antigen.22 Thus, the true preva-
lence of R. conorii infections might be lower than the
percentages of seropositivity.

Second: according to the manufacturer, the test
antigen is not specific for R. conorii and the exact taxo-
nomic status of the rickettsiae present in Dhofar
remains to be determined. R. conorii is antigenically di-
verse23 and, in addition to R. conorii, several new
spotted fever group rickettsial strains have recently
been described from ticks including A. variegatum and
R. turanicus from the Mediterranean and Africa.24-26 We
cannot also exclude the possibility that R. typhi or R.

Ticks collected from do

in the transmission of R

Tick sp
Host
(numbers
sampled) Amblyomma

variegatum

Hyalomma a
anatolicum

Hyalom
drome

Cattle (77) 35 68 42

Camels (21) 32 7 46

Goats (4) 0 0 0

Total 67 75 50
TABLE 2

mestic stock and implicated
ickettsia in Dhofar, Oman

ecies (numbers collected)

ma
darii

Hyalomma

rufipes

Rhipicephalus

spp.
Total

8 16 169

3 15 0 517

0 21 21

5 23 37 707
9

prowazekii, which are not transmitted by ticks, might
occur in Dhofar and cross-react in the serologic test.

Third: it cannot be deduced from the mere
presence of antibodies, whether infections with rickett-
siae represent a significant source of disease in Dhofar,
as serology also detects asymptomatic cases of spotted
fever as well as persisting antibodies.27-29 Observation
of the possible clinical spectrum of the disease should
clarify this point.

CONCLUSION

To our knowledge, this report is the first sero-
logical study of rickettsial infections in the Oman and,
together with the tick survey, demonstrates that trans-
mission of such infection is possible and does occur.
Quantitative epidemiological aspects require further
studies. The population of Dhofar has appreciable
seroprevalence rates for brucellosis20 and toxo-
plasmosis,21 which are also transmitted from domestic
animals to humans. However, the recently improved
living conditions and health services in Dhofar should
significantly reduce the prevalence of these pathogens,
and the diseases transmitted from livestock to humans
in this region should reduce correspondingly.

ACKNOWLEDGEMENTS

We are grateful to the medical and veterinary
practitioners and technical staff in the study localities,
especially Dr M. A. A. Shaban, Director of Health
Affairs, Dhofar and to all individuals who provided
samples. We thank Prof. J. E. Keirans (U.S. National
Tick Collection, Statesboro, GA, U.S.A.) for confirm-
ing the identity of tick specimens, Ms. Angelika

I D R I S E T - A L

Thomschke (Department of Infectious and Tropical
Medicine, University of Munich, Germany) for the gift
of a positive control serum. This study was supported
in part by a travel grant from the Faculty of Theoretical
Medicine, University of Heidelberg.

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Antibodies against rickettsia in humans and �potential vector ticks from Dhofar, Oman

*Idris M A1,2 , Ruppel A2, Petney T3

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?. ????? ? ?. ???? ? ?. ????
METHOD
RESULTS AND DISCUSSION
CONCLUSION
ACKNOWLEDGEMENTS
REFERENCES