Dengue/DHF

Trend of Dengue case and CFR  in SEAR Countries

Nepal

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Dengue fever (DF) is an emerging mosquito-borne disease affecting Nepal. As other vector-borne diseases, outbreak of DF is related with travel and frequent movement of people which is common due to porous border between Nepal and India and socio-cultural and economic activities in cross-border areas.

Initially there were reports of suspected DF outbreaks in Banke district. The clinical observation, pathological and laboratory investigation results proved introduction of DF in Banke, Bardiya, Dang, Kapilbastu, Parsa, Rupandehi, and Jhapa districts. A total of 32 suspected and confirmed DF cases were recorded. So far, 22 cases of DF have been laboratory confirmed and many patients have travel history to India. It was also reported that many patients having similar symptoms visited India for treatment and confirmed as DF. Two suspected, 7 probable and 23 confirmed DF cases were recorded during 2006 outbreak. Seventy-five per cent DF cases were reported in October and few cases were reported in September and November. Only 11 per cent patients had travel history to India in past two week period prior to clinical manifestation of DF. Ninety-four per cent patients were adults and male to female ratio was 4:1.

Aedes aegypti has been identified in 5 major urban areas of Terai region which suggests that DF transmission may occur locally Terai districts if imported cases are introduced.

Nine out of thirty-seven serum samples sent to AFRIMS was positive to DF virus in PCR testing. DEN-1, DEN-3 and DEN-4 have been found in Nepal which indicates the possibility of severe form of disease, i.e. Dengue Haemorrhagic Fever (DHF) during outbreaks. No DF related deaths have been reported in Nepal.

The district-wise distribution of DF outbreaks and Aedes aegypti in Nepal is presented in Fig. 1.

Fig. 1: Distribution of DF Outbreaks and Aedes aegypti, Nepal, 2006

As can be seen from Fig. 1, most DF cases were detected in Terai districts bordering with India. Vector responsible for DF transmission was also identified only in border districts. It clearly indicates that endemic cycle of DF can be generated in these districts. Considering the distribution of DF cases, clusters of cases in urban areas and potentiality for local transmission of DF due to presence of efficient vector, it can be assumed the number of potential DF cases. The estimated number of DF cases is shown in Table 1.

Table 1: Distribution of Estimated and Detected DF Cases, Nepal, 2006

DF cases were recorded in 32 patients residing in 9 districts. Kathmandu and Dhading are hilly districts where Aedes aegypti has not been identified whereas it has been found in 5 sampled districts of Terai region. The first detected DF case from Kathmandu had travel history to India. Interestingly, there were confirmed DF cases having no travel history in Terai districts. It may indicate the potential chance of local transmission of DF. Therefore we have estimated a total of 140 DF cases in Nepal during 2006 which may include imported cases also. Under reporting is expected in the absence of diagnostic facilities at the field level and it may be reported as viral fever or Pyrexia of Unknown Origin (PUO). The temporal distribution of DF outbreak during September to November 2006 is presented in Fig. 2.

Fig. 2: Epidemic curve of DF outbreak, Nepal, 2006

First DF case was reported in Kathamndu in September 11, 2006. The patient had travel history to India. Seventy-five per cent DF cases were reported in October and few cases were reported in September and November. Clusters of DF cases were reported in mid October in Banke and Dang districts which may be indicative of probability of local transmission among patients having no travel history. The distribution of DF patients according to travel history is presented in Fig. 3.

Fig. 3: Travel history of DF Patients, Nepal, 2006

Seventy-five per cent patients reported that they have not traveled any places known as DF affected area. Only 11 per cent patients had travel history to India in past two week period prior to clinical manifestation of DF. The age group distribution of DF patients is presented in Fig. 4.

Fig. 4: Age group distribution of DF patients, Nepal, 2006

Ninety-four per cent patients were adults whereas only 6 per cent were children. It shows that chance of exposure to DF vectors is often associated with outdoor activities particularly in day time. The gender distribution of DF cases is presented in Fig. 5.

Fig. 5: Gender distribution of DF patients, Nepal, 2006

Eighty-one percent patients were male and they are mostly involved in outdoor activities. In addition, they use short sleeve cloths due to hot and humid conditions and therefore frequently exposed to mosquito bites.

Entomological

Entomological study of mosquitoes carried out during eighties revealed the presence of Aedes albopictus in Terai plains which has been reported regularly. Ae. albopictus is considered as an inefficient vector for DF transmission. Previously no Aedes aegypti was recorded in Nepal. Recent outbreak of suspected DF cases prompted to conduct cross-sectional entomological survey to identify the presence of Aedes aegypti. It has been identified in 5 major urban areas of Terai region bordering with India, i.e. Biratnagar (Morang), Birganj (Parsa), Bharatpur (Chitwan), Tulsipur (Dang) and Nepalganj (Banke). Many DF cases have been reported from these or adjoining districts which suggests that DF transmission may occur locally Terai districts if imported cases are introduced.

Laboratory

It is important that National Public Health Laboratory (NPHL) was planning to initiate DF serological study in 2006. National Public Health Laboratory maintains working relationship with AFFRIMS, Bangkok for surveillance of Japanese encephalitis.

DF suspected cases were reported in Nepalganj in October. Rapid diagnostic kits (Panbio Duo) and ELISA test kits were provided to Bheri Zonal Hospital of Nepalganj to detect IgM and IgG. Out of 37 serum samples tested by the NPHL, 8 samples were positive by Pathozyme ®, EIA for the detection of IgG antibodies of OMEGA Diagnostics whereas 4 positive by Dengue Duo Cassette of PanBio. All the 4 rapid test positives were confirmed by EIA whereas EIA 4 EIA confirmed cases rapid test negative. The problem of higher OD value in negative control was encountered during DF serology test. A summary of DF positive test results made available by National Public health Laboratory of Nepal is presented in Table 2.

Table 2: DF laboratory test results, National Public Health Laboratory, Nepal, 2006

Nine out of 37 serum samples taken from DF suspected patients sent to AFFRIMS Bangkok were positive to Dengue virus in PCR testing. It is interesting that 2 ELISA test positive cases were found to be PCR positive whereas 7 samples had same result in ELISA and PCR. It shows the low sensitivity of ELISA test result.  DEN-1, DEN-3 and DEN-4 have been identified in patients living in Kathmandu, Banke, Dang and Parsa districts. Cases recorded in Kathmandu indicate multiple source of infection, i.e. imported cases from different areas. It also indicates the possibility of severe form of disease, i.e. Dengue Haemorrhagic Fever (DHF) during outbreaks. However, DEN-3 was responsible for DF outbreak in Mid West Terai districts.

Response to DF outbreak

The emergence of DF in Nepal created a panic situation because mass media was creating panic situation of DF outbreak in India. Outbreak investigation, identification of potential vectors for DF transmission, laboratory confirmation and clinical case management and outbreak communication were challenging issues. Fortunately laboratory capacity and clinical case management capacity were already in place at the central level which was supported by WHO.

The Epidemiology and Disease Control Division (EDCD) is national focal point for surveillance and response for emerging diseases. The Division distributed public awareness materials, diagnostic test kits and technical information about DF to border district hospitals and District Public Health Offices. Team of experts from EDCD, NPHL was mobilized to conduct clinical orientation and training on rapid diagnostic tests for DF in Biratnagar, Birganj and Nepalganj. Since there is no vaccine and specific drug for treatment of DF patients, it was not an easy task to deal with media, rumour tracking and verifications.

WHO provided technical support for surveillance and outbreak investigation of DF in Nepal. Rapid diagnostic test kits were provided to the National Public Health Laboratory. A team was sent to Nepal to assist the national authority in outbreak investigation of DF.

Conclusion

The clinical observation, pathological and laboratory investigation results proved introduction of DF in Nepal. It is interesting to note that patients from Dang district have no travel history outside Dang valley. Since Aedes aegypti has been identified in Dang, the prevailing epidemiological information strongly suggests the existence of endemic cycle of DF in Dang. Similarly there is no evidence of the presence of efficient vector in Kathmandu and Dhading though travel history of patients claimed that they have not visited endemic area like Terai or India.

Dengue Fever outbreaks have been confirmed for the first time in Nepal which indicated geographical spread of DF area.

Development of appropriate control measures for vector control, capacity building for surveillance, prevention and control of DF, operational research on vector behaviour and social acceptance of control measures and public awareness and education are key areas of public health intervention.

(SOURCE: Outbreak investigation of DF in Nepal, SEARO)