Dr Tayyaba Ijaz INTRODUCTION: Dengue Fever (DF) is transmitted to human beings through the bite of infective mosquitoes carrying the viruses. It is an acute viral illness characterised by sudden onset of fever for two to seven days, severe headache, muscle and/or joint pains, abdominal discomfort and rash, and pain behind the eyeball. It is generally self-limited, manageable and is non-fatal. Dengue Hemorrhagic Fever ((DHF) is a severe, potentially fatal infection that occurs when a person having immunity against one type of dengue virus is reinfected by a different serotype of dengue virus. It is spread by certain mosquitoes named Aedes aegypti, which bite primarily during the day. The case fatality rate of DHF in most countries is about 5 percent, but this can be reduced to less than 1 percent with proper management and treatment. Dengue fever should not be confused with dengue hemorrhagic fever, which is a separate disease and could be fatal. Causes, incidence, and risk factors: DF and DHF are caused by one of the four closely related virus serotypes. Worldwide, more than 100 million cases of dengue fever occur every year. A small percent of these develop into DHF. Secondary dengue infection and the strain of virus is also a risk factor for it. All wild type viruses do not cause severe disease. The age of the patient and host genetics are also major risk factors for the disease. Although DHF can occur in adults, but most cases have been reported in children younger than 15 years, female, or Caucasian. BACKGROUND: DF was first reported in 1779-1780 in Asia, Africa, and North America.The occurrence of outbreaks on the three continents indicates that these viruses and their mosquito vector have had a worldwide distribution for more than 200 years. However, the first recorded outbreak of a dengue disease compatible with DHF occurred in Australia in 1897. A similar hemorrhagic disease was recorded in 1928 in Greece and again in Taiwan in 1931. The first confirmed epidemic of DHF was recorded in the Philippines in 1953-1954. A pandemic of dengue began in South East Asia after World War II and then spread worldwide. Its (DHF) first outbreak appeared in the 1950s, but, by 1975, it became a major outbreak in that region. In the 1980s, it re-emerged in Asia when Sri Lanka, India, and the Maldives Islands had their first major DHF epidemics. Epidemic dengue fever re-emerged in both in Taiwan and China in 1980. Singapore also had a resurgence of dengue/DHF from 1990 to 1994. Pakistan, for the first time, reported outbreak of dengue fever in 1994. In Lahore, it was first time observed in 2006; whereas the second and subsequent epidemics were observed in 2008 and 2010. Once again, a massive and fulminant epidemic has occurred in Lahore in August 2011, and it has also affected various districts in Punjab. The outbreak of DF coincides with the rainy season in this area. Between 1975 and 1995, DF/DHF was present in 102 countries, including 20 countries in Africa, 42 in the Americas, seven in South East Asia, four in the Eastern Mediterranean, and 29 in the Western Pacific. By 2003, 24 countries in the American region reported confirmed DHF cases. In 2005, dengue was reported, as the most important mosquito-borne viral disease affecting humans; its global distribution was comparable to that of malaria, an estimated 2.5 billion people live in areas at risk for epidemic transmission. As many as 100 million people are infected globally each year, according to the US Centres for Disease Control and Prevention (CDC). Epidemiological analysis: The analysis indicates that this emerging infection is rapidly evolving, with increased frequency of outbreaks and its expansion towards the previously unaffected and new geographical areas. The maximum burden is borne by the countries belonging to the Asia Pacific region. Among the estimated 2.5 billion people at risk globally, more than 70 percent of the population (about 1.8 billion) reside in Asia Pacific countries. According to the CDC, there are an estimated 100 million cases of DF with several hundred thousand cases of DHF and require hospitalisation each year. Nearly 40 percent of the world's population lives in an area that is endemic with dengue. Another report indicates that 55 percent of world population (about 3.6 billion people) is at risk in 124 endemic countries. The reports of the Western Pacific Regional Office (WPRO) reveal that it continues with increasing trend; annual reported dengue cases were around 100,000 cases in 2001-2002. The figures gradually increased to 150,000-170,000 cases annually during the period 2003-2006. Since 2007, the region reported over 200,000 cases each year. In 2009, there were 242,424 dengue cases and 785 dengue deaths were reported in 25 countries in the region. These countries included Cambodia (11,699 cases, 38 deaths), Malaysia (41,486 cases, 88 deaths), Philippines (57,819 cases, 548 deaths), and Vietnam (105,370 cases, 87 deaths). During this period, Cambodia continued to see an overall high-level dengue activity, while Singapore has started to see a decline. Cambodia and Vietnam have experienced a higher cumulative number of reported cases in 2011 relative to the same time period in 2010. Current global situation: In Australia, 549 cases were reported with 0 death from January-August 2011; Cambodia 10,256 cases (48 deaths); Lao PDR 2,196 cases (five deaths); Malaysia 13,100 cases (21 deaths); Philippines 63,741 cases (373 deaths) with increased in activity in June and July 2011 relative to May 2011; Singapore 4,013 cases up to end of week 35, and Vietnam 22,853 cases (22 deaths) from January-July 2011, according to WHO. According to the Times of India, the total number of cases reported in New Delhi in this season is 73. However, the number was less as compared to last year when 1,014 cases and three deaths were reported for the same period of time. In Ludhiana, dengue is spreading its tentacles with almost four cases being reported every day in the last two months.As many as 240 patients from the city have tested positive for the disease from July to early September. A total number 112 dengue cases were registered in Ahmedabad and Gujarat States, while in Orissa about 927 samples have been found positive for dengue. According to the International Society for Infectious Diseases (ISID), the number of people hospitalised with dengue fever has increased by more than 25 percent in 2011, as compared with last year 2010 in Pakistan, especially in the province of Punjab. According to the WHO report on dengue situation dated September 1, 2011, a total of 9,451 cases and 44 deaths due to dengue infection, with a case fatality rate of 0.47 percent were reported up to the end of 32nd week of the year. In 2010, a total of 7,403 cases and 19 deaths, with a CFR of 0.26 percent were reported during the same reported time. Factors responsible for the emergence of dengue epidemic: The emergence of DF/DHF has become one of the major public health problems in Pakistan and several factors have been identified that have contributed in the spread of the disease. These factors include: l Uncontrolled and unplanned urbanisation and population growth have resulted in substandard housing, inadequate water sewerage, and waste management systems. This has helped the dengue mosquito in the transmission of disease. l Like other resource-limited countries, deteriorated public health infrastructure, limited financial resources, lack of research-oriented professionals, and negligence in performing individual duties, have put the mankind in a "crisis mentality". They (the experts) put their efforts more on emergency control methods, rather than to develop programmes to prevent the epidemic. As a result, it reaches its peak before its recognition. l Increased travelling by airplanes, trains, and buses provides an ideal mechanism for the transmission of dengue viruses between population, resulting in a frequent exchange of such viruses and other pathogens. l Effective mosquito and larvae control is almost non-existent in most dengue-endemic areas. l The chemicals or insecticides used for mosquito eradication have become resistant to the population of Aedes aegypti. Add to it the non-availability of the system to check the effectiveness of an insecticide. l Agrochemical spray on agricultural settings, substandard or low concentration of chemical spray also contribute towards the development of insecticide resistance. TRANSMISSION OF the DISEASE: The dengue viruses are usually present in the patients blood before the start of symptoms, and remain for an average of five days after the illness. This is a critical period when the patient is most infective for the mosquitoes that act like vector, contributing to maintaining the disease transmission cycle. The virus: The viruses are members of the genus Flavivirus and family flaviviridae. On the basis of antigenic and biological characteristics, the dengue viruses have been further differentiated into four serotypes (DEN-1, DEN-2, DEN-3 and DEN-4). The infection with any one serotype confers lifelong immunity against the particular virus serotype, but it does not cross-protection for other serotypes. Upon the exposure of other serotypes, the situation can lead to cause DHF epidemics associated with severe and fatal disease. The vector: Dengue viruses are transmitted from person to person by the Aedes (Ae.) mosquitoes of the subgenus Stegomyia. Ae. aegypti is the most important epidemic vector, but the other species such as Ae. albopictus, Ae. polynesiensis, Ae. niveus and members of Ae. scutellaris complex, have also been reported as secondary vectors. All are generally less efficient epidemic vectors than Ae. aegypti. After virus incubation for 8-10 days, an infected mosquito is capable of transmitting the virus to susceptible individuals for the rest of the life of the virus that is 15-65 days. The host (patients): Dengue viruses infect humans and several species of lower primates. But humans are the main urban host of the viruses. Also, monkeys are infected, like human beings, and act as reservoir hosts. MECHANISM FOR THE TRANSMISSION OF DISEASE: The female mosquito most probably Aedes aegypti becomes infected with dengue virus when it sucks the blood from a patient having the infection. The salivary glands present in the body of the mosquito support the virus to multiply rapidly. After incubation for a period of 8-10 days, the virus is transmitted when the infective mosquito bites and transmits the salivary fluid (containing virus) into another person. It is important that an infected mosquito is capable of transmitting the virus to a person for the rest of the life of the virus that is 15-65 days. After 3-14 days of the bite, there is often a sudden start of the disease. Viruses are usually active in the blood of the patient at the time of the appearance of disease and remain for about five days after the illness. This is the patients most infective phase and most favourable for the vector mosquito that gets the opportunity to have a bite, thus maintaining the transmission cycle of the disease. DENGUE AND DENGUE HEMORRHAGIC FEVER: Clinical presentation: Dengue virus infection may be asymptomatic or may cause undifferentiated febrile illness (viral syndrome), dengue fever (DF), or dengue hemorrhagic fever (DHF), including dengue shock syndrome (DSS). The clinical presentation depends on age, immune status of the host, and the virus strain. l Undifferentiated fever: Infants, children and some adults, who have been infected with dengue virus for the first time (i.e. primary dengue infection) develop a simple fever. l DF: The fever begins with sudden onset of high fever - often to 104-105F, headache, and later on the appearance of severe joint and muscle pains. A flat, red rash may appear over most body parts. Then measles-like rashes appear later; the patients become uncomfortable due to increased skin sensitivity. However, those who are diagnosed early and given appropriate therapy can recover completely from the disease. Although DF is commonly benign, it may be a devastating disease with severe muscle and joint pain (break-bone fever), particularly in adults, and occasionally with unusual haemorrhage. l DHF: It is characterised by an acute onset of fever and associated with non-specific constitutional signs and symptoms. There is a hemorrhagic diathesis and a tendency to develop fatal shock (dengue shock syndrome DSS). Abnormal haemostasis and plasma leakage are the main patho-physiological changes, with low platelets count and hemo-concentration presenting as constant findings. Laboratory findings: Low platelet count >100,000/cu.mm3, low WBC count, hemoconcentration; (haematocrit increased by 20 percent or more). This criteria is sufficient to establish a clinical diagnosis of DHF. In cases with shock, a high haematocrit and marked low platelet count support the diagnosis of DHF/DSS. (To be continued) Email:tayyabalhr@yahoo.com