key: cord-0006462-wxparyeg authors: Khanna, M.; Kumar, P.; Choudhary, K.; Kumar, B.; Vijayan, V. K. title: Emerging influenza virus: A global threat date: 2008-11-01 journal: J Biosci DOI: 10.1007/s12038-008-0066-z sha: ecae49cab3db5b32daf600ddea2f2de79bfafd9e doc_id: 6462 cord_uid: wxparyeg Since 1918, influenza virus has been one of the major causes of morbidity and mortality, especially among young children. Though the commonly circulating strain of the virus is not virulent enough to cause mortality, the ability of the virus genome to mutate at a very high rate may lead to the emergence of a highly virulent strain that may become the cause of the next pandemic. Apart from the influenza virus strain circulating in humans (H1N1 and H3N2), the avian influenza H5N1 H7 and H9 virus strains have also been reported to have caused human infections, H5N1 H7 and H9 have shown their ability to cross the species barrier from birds to humans and further replicate in humans. This review addresses the biological and epidemiological aspects of influenza virus and efforts to have a control on the virus globally. The major cause of health concern that claims a large number of lives worldwide every year are the infectious diseases (Ministry of Health Report 1920). The advent of antibiotics and vaccines has lessened the impact of a number of infectious diseases but they are still the number one cause of mortality. These emerging infectious diseases can either be new emergent infections or rare infections that may reemerge occasionally or they may be common infections which increase owing to issues like social instability or resistance development (Ridley 2004) . Of all the infectious diseases, infl uenza deserves the particular attention as it undergoes a high rate of antigenic change giving rise to a new type of infl uenza strain for which there is no immunity in the population. Moreover in the absence of ready or preventive therapeutic interventions, it poses a great threat. Human infl uenza viruses of at least three haemagglutinin subtypes, H1, H2 and H3 have emerged as important pathogens and are of major global health concern. Recently, the infl uenza virus with subtype H5, mutated from H7, has also emerged as a human pathogen and they are more lethal than the earlier strains (Webby and Webster 2003) . Of infl uenza A, B and C viruses, infl uenza A viruses mutate more rapidly thus showing more antigenic fl exibility and hence are more virulent than the other two types (Eccles 2005) (table 1) . They have a range of hosts that include humans, horses, pigs, sea mammals and birds. Each of the haemagglutinin sub-type can combine with all the subtypes of the neuraminidase, resulting in huge and highly fl exible pool of genetic diversity. The emergence of any novel HA subtype to which a population does not have any immunity could lead to a pandemic. Amantadine, rimantidine sensitive no effect no effect Zanamivir (Relenza) sensitive sensitive Surface glycoproteins 2 2 (1) As infl uenza is caused by a variety of species and strains of viruses, in any given year some strains can die out while others create epidemics with a potential to cause a pandemic. The incubation period of this virus is generally 1-4 days, with an average of 2 days (Khanna et al 2002) . The adults transmit infl uenza one day prior to onset of symptoms and up to 5 days after the symptoms begin. The children usually transmit it for 10 or more days (Elveback et al 1976) . The groups of people that are at a high risk for contracting infl uenza and infl uenza related complications include (Mathew 2006 (Areechokchai et al 2004; Dinh et al 2006) . In urban areas, where poultry raising is uncommon, a risk factor for H5N1 disease appears to be visiting a live poultry market (Yu et al 2007) . This suggests that environmental factors could play a role in H5N1 virus transmission to humans. In up to a quarter of cases, a source of H5N1 virus exposure could not be identifi ed (Sedyaningsih et al 2007) . Clusters of two or more epidemiologically linked H5N1 cases have been identifi ed in several countries (Olsen et al 2005) . Approximately 25% of all H5N1 cases reported to date have occurred in clusters. Most clusters have involved two to three cases; the largest to date was eight cases (seven confi rmed one probable) with seven deaths. While most cluster cases probably acquired H5N1 virus infection through common poultry exposures, limited, non-sustained human to human H5N1 virus transmission through close, prolonged, unprotected contact with a severely ill H5N1 patient has probably occurred or could not be excluded in some clusters Kandun et al 2006) . Probable, limited, human-tohuman transmission in health care settings has been reported in health care workers and family members . Nearly all H5N1 cluster cases have occurred among blood-related family members, suggesting a possible role of genetic susceptibility. The occurrence and frequency of clinically mild and asymptomatic H5N1 virus infection are unknown. A sero-prevalence study among 1525 Hong Kong poultry workers in 1997 found that 10% had H5N1 neutralizing antibodies (Bridges et al 2002 The pandemics caused by the infl uenza A viruses in the past have led to a high level of illness, death, social disruption and economic loss (Kawaoka et al 1989; Palese et al 2004; WHO, Geneva 2005) (table 2) . Today, the H1N1 and H3N2 strains are the commonly circulating strain in the human population (Palese et al 2004) . Since 1997, a highly pathogenic avian strain, H5N1, have been found to cross the species barrier from birds to humans leading to 100% mortality in humans. The earlier less virulent avian strain H9N2 along with H5N1 strain which is far more virulent and has crossed the species barrier to humans and deaths in humans due to this strain has been reported from many countries (table 3) . The persons who are in regular contact with fowls and their products or excreta, have a chance to be infected with the deadly strain provided the fowl has been infected with infl uenza virus. The human to human transmission of this virus can lead to a great pandemic (Stephenson et al 2004) . The disease is usually most severe in very young children (under 5 years of age) and the elderly. Many people are so ill that they are confi ned to bed for several days, with aches and pains throughout their bodies, which are worst in their backs and legs (Eccles 2005 (Kerr et al 1975) Common symptoms of the fl u such as fever, headaches, and fatigue come from the huge amounts of proinfl ammatory cytokines and chemokines (such as interferon or tumour necrosis factor) (Eccles 2005; Schmitz et al 2005) produced from infl uenza-infected cells. Of the symptoms listed above, the combinations of fi ndings including fever, cough, sore throat and nasal congestion can improve diagnostic accuracy (Call et al 2005) . A measure of the severity of infl uenza in any one year is the excess of deaths due to pneumonia or infl uenza compared to the seasonally adjusted norm. The infl uenza A subtypes currently circulating in humans, H1 and H3, continue to experience the antigenic changes. Although the potential of H1N1 and H3N2 strains are diminishing, as their ability to cause serious disease has become increasingly attenuated, the continual modifi cation may lead to an increase in virulence. The World Health Organization (WHO) maintains constant surveillance of infl uenza outbreaks world wide and has a series of 'sentinel' labs to look at what is happening in the circulating virus population. It has a network of 112 National Infl uenza Centers that monitor infl uenza activity and isolate infl uenza viruses in all continents. The Center for Disease Control and Prevention (CDC) does the same in the United States and co-operates with WHO. In India, Department of Health and Human Services (DHHS)-CDC in collaboration with Indian Council of Medical Research (ICMR) is involved in the intensive infl uenza surveillance programme. National Institute of Virology, Pune is the referral center for the ongoing infl uenza surveillance programme which controls all the regional centers. The main objectives of the surveillance programme, are establishment of epidemiological and virological infl uenza surveillance network in different geographical areas of India, development of human resource through training and strengthening of infrastructure, expansion and strengthening of the surveillance in a phased manner, timely dissemination of information generated and improvement of awareness and contribution of the infl uenza strains and information generated to the global infl uenza surveillance. Large number of suspected infl uenza speciemens were collected from various centres .A total number of 364 isolates were found positive for H3N2, H1N1 and B infl uenza virus, out of which 273 isolates were sequenced for HA gene and sent to CDC, US. The sequence analysis shown that most of the isolates were sensitive against Adamantane while some were resistant for the same. A number of tests help in the diagnosis of infl uenza (table 4) . Specimens are preferably collected within the fi rst 4 days of illness. Rapid infl uenza tests provide results within 30 min or less; viral culture provides results in 3-10 days.Routine serological testing for infl uenza requires paired acute and convalescent sera and does not provide results to help with clinical decision-making. Broadly the techniques are classifi ed as direct and indirect diagnostic techniques. The Direct method involves detection of direct presence of viral particles, viral antigens, and viral genome through sirect immunofl ourescence (Spada.et al 1991) , Enzyme linked immunosorbent assay (Orskov and Orskov 1990) , Antigen capture and staining of cells with monoclonal antibody (Brumback and Wade 1996) . Other methods are indirect where the clinical samples may be inoculated in cell cultures, eggs, or animals for growth of the virus and its further typing. Hen's eggs and cell lines are used for virus growth. Many continuous cell lines are being employed for infl uenza virus growth like MDCK, LLC-MK2 etc. (Davies.et al 1978) . The most common used cell line is MDCK. The presence of virus is detected by the cytopathic effect (CPE) like slow rounding and degeneration of cells. Further confi rmation of infl uenza virus is done by by haemagglutination test and haemagglutination-inhibition test which are used for routine diagnosis (Hirst 1941) . In recent years molecular techniques are being increasingly used for diagnostics. The advantage of these techniques is its sensitivity and quick turnaround time. Some molecular techniques for infl uenza diagnosis include reverse transcriptase polymerase chain reaction (RT-PCR), multiplex PCR, real time RT-PCR, nucleic acid based amplifi cation (NASBA) and loop mediated isothermal amplifi cation (LAMP) (Khanna and Srivastava 2006) . The most commonly used technique for rapid detection of infl uenza viruses is RT-PCR. It is extremely sensitive and rapid (Wright et al 1995) . A reverse multiplex PCR is employed for typing and subtyping of number of different infl uenza strains together. The appropriate combination of primer sets and optimizations of PCR conditions allow formation of multiplex PCR for detection of infl uenza A (H1N1 and H3N2) and B from clinical samples (Stockton 1998) . The advent of molecular methods such as real time PCR has allowed improvement of detection methods currently used in laboratories, although not all of these methods include an internal positive control (IPC) to monitor for false negative results. A one-step reverse transcription real time PCR (RRT-PCR) with a minor groove binder (MGB) probe, for the detection of different subtypes of AIVs (against the HA and NA gene) has also been (Lee and Suaraz 2004) designed. The PCR is performed and the corresponding graphs indicate the type, sub-types and amount of the viral strains without performing agarose gel analysis (Trani et al 2006) . Most recent rapid, sensitive technique which is not found to be affected by other biological compounds in the clinical samples is called loop mediated isothermal amplifi cation (LAMP) which is conducted under isothermal conditions of 60-65 ˚C by using enzyme called Bst DNA polymerase. Thus, it is able to quantify the amount of DNA accurately without being affected by presence of other inhibitory substances (Poon et al 2005; Kaneko 2007) .Thus more and more sensitive techniques must be explored for the development of effi cient and effective strategies against infl uenza. Infl uenza causes signifi cant morbidity and mortality and is responsible for considerable medical expenditures. Antiviral therapy and vaccination are important strategies for the control of human/ avian infl uenza, but the effi cacy of these modalities is limited by the timings of administration and shortage of supply. Healthcare workers currently must apply strict standards, contact and droplet precautions when dealing with suspected cases, and upgrade to airborne precautions when performing aerosol-generating procedures. Non-pharmacological measures such as early case isolation, household quarantine, school/workplace closure, good community hygiene and restrictions on travel are useful measures in controlling a pandemic Tambyah 2008) . High Security Animal disease Laboratory (HSADL), Bhopal and National Institute of Virology, Pune have developed testing kits for avian infl uenza virus in bird droppings to detect the avian fl u at the earliest. Special task forces are set up under the supervision of the Chief Medical Offi cers at each district to spread information about the disease and to monitor all suspicious cases of infl uenza. Indian Council of Agricultural Research (ICAR) has developed bird fl u vaccine to control the spread of the virus and also for vaccination in anticipation of an outbreak. Rimantadine and amantadine are the two well known antivirals to prevent and treat infl uenza A. Amatadine and rimantadine are M2 inhibitors and block virus entry across the endosome and also interfere with virus release (Wang et al 1993) . They are good prophylactic agents for infl uenza A and may be given as protective agents during an outbreak, especially to those at severe risk and key personnel. They may also be given at the time of vaccination for a few weeks, until the humoral response has time to develop. (There is some evidence that these drugs can help prevent more serious complications and reduce the duration of infl uenza A, if given early.) However, in the 2005-2006 infl uenza seasons, 92% of H3N2 strains examined had mutations that would confer resistance to these drugs as did 25% of the H1N1 strains tested. Similar problems were seen in 2006-2007 and so these drugs are not recommended until the percent resistance in the major circulating type drops. The resistance to amantadine and rimantadine is detected by sequencing the M2 gene which detects the point mutations responsible for imparting the resistance (Belshe et al 1988; Hayden et al 1992; Abed et al 2005) . Two neuraminidase inhibitors (Zanamivir [Relenza] and Oseltamivir [Tamifl u]) have also been approved by the Food and Drug Administration (FDA) for prophylaxis as well as treatment (Gubareva et al 1998; Monto et al 1999) . They are active against both infl uenza A and infl uenza B and can reduce the duration of uncomplicated infl uenza (by approximately 1day in about 70-90% of adults) if taken within two days of the onset of illness. Low-dose steroids may be considered in the treatment of refractory septic shock. Noninvasive positive pressure ventilation (NPPV) may play a limited supportive role for acute lung injury, but it is contra-indicated in critically ill patients with multi-organ failure and haemodynamic instability. Intravenous gammaglobulin should be used with caution for treatment of reactive haemophagocytosis due to its thrombogenic effects, whereas the role of etoposide needs evaluation with animal models Tambyah 2008 ). Infl uenza vaccine is often recommended for high-risk groups, such as children and the elderly. Infl uenza vaccines can be produced in several ways; the most common method is to grow the virus in fertilized eggs of hens (Osterholm 2005) . A new vaccine is formulated annually with the types and strains of infl uenza predicted to be the major problems for that year (predictions are based on worldwide monitoring of infl uenza). The vaccine is multivalent (trivalent) and the current one, recommended by WHO, is to two strains of infl uenza A (one for H1N1 and one for H3N2) and one of infl uenza B. It has a short lived protective effect and is usually given in the fall so that protection is high in December/January -the usual peak months for fl u in the northern hemisphere. In India, the poor population especially children living in slums and other over crowded areas should be targeted for vaccination in the start of November. About two weeks after vaccination, the antibodies that provide protection against virus infection develop in the body. (Belshe et al 2000a, b; Dunnil 2006) . can be grown in eggs until it loses virulence and the avirulent virus given as a live vaccine (Hilleman et al 2002) . Attenuation is done by multiple changes in the various genome segments. Reassortment is used to generate viruses which have six gene segments Emerging infl uenza virus: A global threat from the attenuated virus and the HA and NA coding segments from the virus which is likely to be a problem in the up-coming infl uenza season (Jin et al 2003; Hoffman et al 2005) . Human infections with highly pathogenic avian infl uenza A Human infl uenza outbreak has the potential of triggering a pandemic when a new infl uenza virus appears against which the human population has no immunity. With the increase in global transport and communications, as well as urbanization and overcrowded conditions, epidemics due to the new infl uenza virus are likely to quickly take hold around the world leading to enormous numbers of deaths and illness. Outbreaks of infl uenza in animals, especially when happening simultaneously with annual outbreaks in humans, increase the chances of a pandemic through the merging of animal and human infl uenza viruses. During the last few years, the world has faced several threats with pandemic potential, making the occurrence of the next pandemic just a matter of time. A surveillance network has been developed by WHO for rapid detection of unusual infl uenza outbreaks, isolation of possible pandemic viruses and immediate alert to the WHO system by national authorities for mounting a timely and effi cient response to pandemics. Ensuring an adequate system for alert, response and disaster management should be the basis of every national pandemic preparedness plan. In India, the Ministry of Health and Family Welfare has developed well coordinated strategies for Infl uenza Pandemic Preparedness which aims at reducing the morbidity and mortality due to infl uenza and decreasing social disruption and economic loss. The phasing of pandemic preparedness, action plan and response has been done in accordance with the WHO classifi cation system (2005) in which the Inter Pandemic Period, Pandemic Alert Period and Pandemic Period has been divided into six phases to tackle the tough future pandemic situation. The action plan includes (i) developing plan with co-ordination at international, national, state and district level for preparedness and response, (ii) identifying the roles and responsibilities of all stake holders, strong virological surveillance for early detection of novel virus, (iii) institutionalizing mechanism for developing suffi cient quantity of vaccines, (iv) ensuring availability of adequate quantity of anti viral drugs, (v) strengthening hospital systems and planning for optimum utilization of services institute public health measures including infection control practices, (vi) establishing effective communication with community health care providers and the media, and (vii) establishing synergies with other existing programmes / schemes for optimal utilization of resources. A major component of pandemic preparedness is to strengthen the capacity to respond to yearly epidemics of infl uenza, investment in pandemic vaccine research and promoting domestic production of infl uenza vaccines The challenges are great but the costs of failure are potentially so catastrophic that it is imperative for the international community to ensure that the efforts and endeavors are given the best possible chance of success. 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