Experts are worried that the people who survived Dengue last year in Karachi are at risk this year again but nothing is being done to monitor them. It is known that there are three stages to the Dengue virus with Dengue Shock Syndrome being the last one that can prove fatal.
Last year, 1,200 suspect cases and 260 confirmed dengue cases were reported to Abbasi Shaheed Hospital alone. Twenty-two people died. The 1,200 suspect cases were treated and sent home. Of the 238 confirmed cases that survived dengue, all but one were treated and discharged. One patient, 35-year-old Adnan, died a few months ago. The cases that are currently reporting to ASH are those who were infected last year, excluding one recent case of 20-year-old Gul Zehra of North Karachi, who died of dengue on July 23.
It is thus extremely important that the authorities monitor the 238 ASH cases, not to mention the others who reported to other hospitals in Karachi and across Sindh.
In addition to these worries, experts point out that as with most viruses, the Dengue virus is also capable of mutating or changing. Experts from the Aga Khan University Hospital and the Centre for Emergency Preparedness and Response, UK got together to study the two strains of the dengue virus in the 2006 outbreak of dengue hemorrhagic fever in Karachi. Their findings have appeared online this month for the Journal of Clinical Virology. They warned that the types of dengue involved in the recent epidemic outbreaks in Pakistan are not well defined.
The experts sought to analyze the predominant strain responsible for the most severe and largest outbreak of dengue hemorrhagic fever (DHF) that hit Karachi in 2006. Out of 250 patients at AKU, they concluded that strains DEN-2 and DEN-3 were responsible for the 2006 outbreak. The introduction of a new strain (DEN-3) and or a shift of DEN-2 are the probable factors for the recent outbreak of DHF in this region.
The global epidemiology of dengue fever/dengue hemorrhagic fever (DF/DHF) is changing fast. In recent years, the disease has changed its course, and now regularly manifests in severe form as DHF and with increasing frequency of out-break. The first known epidemic of DHF occurred in the city of Manila, Philippines in 1953–1954. It has now expanded geographically from Southeast Asian countries to Asian countries including India, Pakistan and Sri Lanka.
The distribution of DHF and Dengue Shock Syndrome (DSS) in Asia has been particularly intriguing. Before 1989, DHF was common in Southeast Asia but rare in the Indian Sub-continent despite the circulation of all four types in both regions. After 1989, this pattern of disease changed and regular epidemics were reported from the Indian subcontinent. The first major out-break of DHF in Delhi occurred in 1996, and despite its endemic nature, Dengue virus type 2 (DEN-2) was identified as the agent for this outbreak. Following this, another out-break of DHF was reported in 2003 and this time all four types of dengue viruses were found in circulation.
Epidemic outbreaks of DF and DHF have been reported from Pakistan since 1994. However, the status of dengue types involved in the epidemic outbreaks in Pakistan is not well defined. In 1994 experts reported dengue virus type 1 (DEN-1) and DEN-2 in three of the 10 patients tested during the outbreak.
Pakistan was conspicuously absent from the WHO listing for South East Asian countries endemic for dengue until 1993. The first confirmed outbreak from Pakistan was reported in 1994. Strains DEN-1 and DEN-2 were reported in three patients. A combination of strains DEN-1 and DEN-2 was perhaps also responsible for the resurgence of DF in 1998 in children.
DEN-3 has been reported as the cause of severe DHF outbreaks in India, Bangladesh and Sri Lanka and has emerged as a major strain in the region. In addition, DEN-3 has also been responsible for a severe form of DHF in Mexico. The emergence of DEN-3 in Pakistan is a recent finding, and was first reported from patients with DHF during an outbreak in 2005. The Karachi strain was found to be related to the dengue virus type 3 isolated in Delhi that was responsible for the DHF outbreak in 2004. The introduction of this new type is perhaps one of the factors leading to the severe form of DHF outbreak in Karachi. Further studies are required to confirm this association in detail.
Evidence suggests that DEN-2 has been in the Asian Subcontinent since 1967 and has evolved by replacing type V (New Delhi outbreak strain 1967) with type IV strains in 1996; this shift in the genotype resulted in a major outbreak of DHF in New Delhi. A similar association has been reported from Sri Lanka.
In the AKU study, they found DEN-2 to be the dominant type involved in the 2006 outbreaks in Karachi. Moreover, patients with DHF were more frequently associated with DEN-2 when compared with DEN-3. Prior to the filing of this report, 20 patients with DF/DHF in June 2007 tested positive for DEN-2.
Absence of DEN-1 in the 2006 outbreak in Karachi is an interesting finding. In India, DEN-1 was a predominant type during 1997–2004. In 2005, however, DEN-3 replaced DEN-1 and became the dominant strain. We can speculate that this shift may be replicated in Karachi, however, large population-based studies would be required to confirm this.
The circulation of two Dengue types classifies Pakistan a