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Letter
Ehrlichia ruminantium,
Sudan
Yasukazu Muramatsu,*
Shin-ya Ukegawa,* Abdel Rahim Mohamed El Hussein,† Magdi Badawi Abdel
Rahman,† Khalil Mohamed Ali Abdel Gabbar,‡ Agnes Mumbi Chitambo,§ Tomoyoshi
Komiya,¶ Enala Tembo Mwase,# Chiharu Morita,* and Yutaka Tamura*
*Rakuno Gakuen University, Hokkaido, Japan; †Center of Veterinary Research
Laboratories, Khartoum, Sudan; ‡University of Bahr El Gazal, Khartoum,
Sudan; §University of Namibia, Windhoek, Namibia; ¶Kitasato Institute
Research Center for Biologicals, Saitama, Japan; and #University of Zambia,
Lusaka, Zambia
Suggested
citation for this article
To the Editor: Ehrlichia ruminantium, the causative agent
of heartwater, is transmitted by Amblyomma spp. ticks. Amblyomma
variegatum ticks, which are found in the Caribbean and sub-Saharan
Africa, except in certain areas of southern Africa, are major vectors
of E. ruminantium (1–3). A. lepidum is
also an important vector of heartwater, especially in eastern Sudan (4).
However, few epidemiologic data exist on infection rates of Amblyomma
spp. ticks and distribution of E. ruminantium in Sudan. A polymerase
chain reaction (PCR) assay that uses DNA probe pCS20 has been developed
for detecting E. ruminantium (5). Another PCR
assay for the major antigen protein 1 gene (map1) has been used
to differentiate strains of E. ruminantium (6,7).
These PCR assays have high sensitivity and specificity for the amplification
of E. ruminantium DNA (6,8). For epidemiologic
study of E. ruminantium in Sudan, we used PCR to detect E. ruminantium
DNA in ticks. We also sequenced PCR products to identify the genotype
of E. ruminantium.
The pCS20 DNA fragment of E. ruminantium was detected in 8 (8.2%)
of 97 A. variegatum ticks and 2 (1.9%) of 106 A. lepidum
ticks (χ2= 3.123, by Yates correction). The nucleotide
sequences (279 bp) obtained from 5 A. variegatum ticks and 1 A.
lepidum tick were identical (GenBank accession no. AB218277). The
sequences were similar to those of Welgevonden, Vosloo, and Ball3 strains
from southern Africa and Gardel strain from the Caribbean islands (similarity
= 99.64%). The pCS20 sequences obtained in this study were different from
those of strains from western Africa.
An 855-bp map1 nucleotide sequence obtained from 1 A. lepidum
tick was provisionally named Gedaref (GenBank accession no. AB218278).
The nucleotide sequence of Gedaref was found to be closely related to
those of Senegal and Pokoase strains from western Africa and to South
Africa Canine and Kümm1 strains from southern Africa (similarity = 90.53%–97.43%).
Gedaref clustered with these 4 strains and with 6 other strains, including
Kiswani from eastern Africa and Antigua from the Caribbean islands (Figure).
In contrast, the nucleotide sequence of Gedaref showed 84.8% similarity
with that of Um Banein, which has been known as the only strain of E.
ruminantium in Sudan. Um Banein formed another cluster with Gardel,
Lutale, and Umpala strains from southern Africa (Figure).
The map1 coding sequence of Gedaref was closely related to those
of strains Senegal, Ball3, South Africa Canine, and Pokoase (similarity
= 92.61%–97.97%). Gedaref and these 4 strains formed a cluster and branch
with Um Banein (similarity = 87.6%).
The novel E. ruminantium genotype Gedaref was detected in A.
lepidum by PCR assays. This work has shown that another strain of
E. ruminantium, in addition to the Um Banein strain, is present
in Sudan. Since the Um Banein strain of E. ruminantium was isolated
from sheep in 1984 (4), no other strain had been reported
in Sudan. The map1 sequence of Gedaref has diverged from that of
Um Banein. Gedaref formed a cluster with several strains that originated
in southern and western Africa. As previously reported, the variation
of map1 sequences of E. ruminantium strains does not reflect
the geographic distribution of the strains (6). However,
Gedaref was distinctively differentiated from the Um Banein strain. Gedaref
was closely related to 3 southern African strains and a Caribbean strain
in the pCS20 sequence but different from western African strains. The
pCS20 sequence has been highly conserved among strains from western Africa
(10), and the distribution of A. lepidum is limited
to eastern Africa (3). If one considers the distribution
of A. lepidum, results of genetic analyses in the pCS20 gene regions
of Gedaref are important for epidemiologic research on E. ruminantium.
We detected pCS20 DNA specific for E. ruminantium in A. variegatum.
This tick is widely distributed in Africa and is the most efficient vector
of heartwater (3). Nevertheless, detection of E. ruminantium
in A. variegatum in Sudan had not previously been reported. Our
results show that A. variegatum is also an important vector of
E. ruminantium in Sudan. A. variegatum ticks are also found
North and South America, Southeast Asia, and Australia (3).
Thus, the potential spread of E. ruminantium to livestock is a
continuous threat in these regions from the importation of tick-infested
and subclinically infected wild animals from Africa and the importation
of livestock from Caribbean islands (1,2). We believe
that A. variegatum plays an important role in the spread of heartwater
because of its ability to adapt to various environments.
This article has
been published with permission of the director general of the Animal
Resources Research Corporation, Khartoum, Sudan.
This work was supported
by Gakujyutsu-frontier cooperative research at Rakuno Gakuen University;
the High-Tech Research Center at Rakuno Gakuen University; a grant-in-aid
for cooperative research from Rakuno Gakuen University (2003); and a
grant-in-aid for scientific research (C) (14560272) from the Ministry
of Education, Science, Sports, and Culture of Japan.
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Suggested citation
for this article:
Muramatsu Y, Ukegawa
S, El Hussein ARM, Rahman MBA, Gabbar KMAA, Chitambo AM, et al. Ehrlichia
ruminantium, Sudan [letter]. Emerg Infect Dis [serial on the Internet].
2005 Nov [date cited]. Available from http://www.cdc.gov/ncidod/EID/vol11no11/05-0744.htm
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