Dengue Virus, Bhutan | CDC EID

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Volume 15, Number 10–October 2009
Dispatch
Diversity and Origin of Dengue Virus Serotypes 1, 2, and 3, Bhutan
Tandin Dorji, In-Kyu Yoon, Edward C. Holmes, Sonam Wangchuk, Tashi Tobgay, Ananda Nisalak, Piyawan Chinnawirotpisan, Kanittha Sangkachantaranon, Robert V. Gibbons, and Richard G. Jarman
Author affiliations: Ministry of Health, Thimphu, Bhutan (T. Dorji, S. Wangchuk); United States Army Medical Command–Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand (I.-K. Yoon, A. Nisalak, P. Chinnawirotpisan, K. Sangkachantaranon, R.V. Gibbons, R.G. Jarman); The Pennsylvania State University, University Park, Pennsylvania, USA (E.C. Holmes); National Institutes of Health, Bethesda, Maryland, USA (E.C. Holmes); and Ministry of Health, Gelephu, Bhutan (T. Tobgay)

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Abstract
To determine the serotype and genotype of dengue virus (DENV) in Bhutan, we conducted phylogenetic analyses of complete envelope gene sequences. DENV-2 (Cosmopolitan genotype) predominated in 2004, and DENV-3 (genotype III) predominated in 2005–2006; these viruses were imported from India. Primary dengue infections outnumbered secondary infections, suggesting recent emergence.

Dengue infections have increased worldwide in recent decades. Before 1970, only 9 countries had experienced epidemics of dengue hemorrhagic fever; by 1996, this number had increased to 102 (1). Dengue is endemic to most of Southeast Asia; high numbers of cases are reported each year in Laos, Cambodia, Vietnam, Singapore, and Thailand. Dengue was first reported in Nepal in 2004 (1). Serologic testing of a group of febrile patients in Nepal showed that 8% had immunoglobulin (Ig) M against dengue, and a recent report noted 11 serologically confirmed dengue cases in 2006 (2,3). The Armed Forces Institute of Medical Sciences (AFRIMS) in Bangkok, Thailand, recently confirmed the presence of all 4 dengue serotypes in Nepal (4).

Figure 1 (please, see the full-text)

Figure 1. A) Maximum likelihood phylogenetic tree of 264 complete envelope gene sequences of dengue virus serotype 2 (DENV-2)..


Figure 2 (please, see the full-text)

Figure 2. A) Maximum-likelihood phylogenetic tree of 264 complete envelope gene sequences of dengue virus serotype 3 (DENV-3)...


Appendix Figure (please, see the full text)

Appendix Figure. Map of Bhutan. Selected cites are indicated by enclosed circle and elevation of the city in meters in parentheses.

In another Himalayan nation, Bhutan, dengue was first suspected in the summer of 2004. Bhutan is an extremely rugged and mountainous country of 38,394 km2 with an altitude ranging from 150 m on the southern border with India to >7,000 m in the mountains bordering Tibet (Appendix Figure). The dengue outbreak resulted in 2,579 cases (5), almost all of which occurred in and around Phuntsholing district (2005 census population 20,537) in southern Bhutan on the border with India. Fifty-two serum samples from this outbreak were tested by using dengue enzyme immunoassay (EIA) at the National Institute of Communicable Diseases, New Delhi, India. Twelve (23%) samples were positive for antidengue IgM. Thirty-five (67%) of the 52 samples also were tested at Suraksha Hospital, Kolkata, India, of which 5 were positive.

Since the initial report in 2004, fewer clinical cases were reported from Bhutan in 2005 and 2006; dengue virus 3 (DENV)-3 was the dominant serotype (5). Although some serologic analysis is available, serum samples from Bhutan have not been evaluated for dengue by using molecular techniques. In particular, circulating DENV in Bhutan has not been genetically characterized, so from where and how frequently DENV is imported into Bhutan are unclear.


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