Aetiology and pathogenesis.
Influenza is a disease which is commonly referred to as flu and is caused by a contagious virus. The virus is known as influenza virus A or influenza virus B. The target of this virus is mostly the human's respiratory organs which are situated in the upper side of the body. They are nose, bronchi, lungs and throat. Influenza usually occurs when changes in the season take place. It generally comes around during winter and autumn in temperate areas (Moghadami, 2017). This disease is a worldwide problem and is a very big reason for mortality all over the world. As per the data represented by the World Health Organization, 2020 it can be seen that the influenza virus has shown lower activity in this year which was not expected. In the temperate zones, the virus has not started to spread yet. Also, in the southern hemisphere, very less number of cases was detected even when the influenza virus testing has increased. However, in Central American and Caribbean countries, detection of sporadic influenza was reported. In tropical Southern America, Southern Asia, South East Asia and tropical Africa no cases of sporadic influenza were detected. With that, it was found that seasonal influenza virus B was majorly the cause of detection (World Health Organization, 2020). In Australia, the activity of influenza is below than average in the year 2020. The number of cases which are confirmed by laboratory testing also remained less since the middle of the March. Its impact on society is very minimal. There were 21,079 cases of laboratory testing from them only 36 were confirmed as having influenza. It was also observed the most cases happened because of influenza virus A (Department of Health, Australian Government, 2020).
People generally catch the infection when they come in contact with droplets which are released from a person who is already suffering from influenza. These droplets are emitted out when the diseased person cough or sneezes. If the diseased person is within the radius of 1 meter of the healthy individual then there are chances that the healthy individual might also get the infection. Transmission could also help when a person comes in direct contact with contaminated surfaces (Moghadami, 2017).
However, people could recover from this disease but sometimes due to complication their case can worsen and they might also die from the infection. Women who are pregnant and those with already existing medical conditions like cardiovascular diseases and diabetes mellitus have to be more alerted from this virus as these people are more vulnerable and susceptible. Moreover, people who have immunodeficiency problem are also at high risk from this disease (Moghadami, 2017; Spoto et al., 2019).
The influenza virus is from the family of Orthomyxoviridae (Moghadami, 2017). It is an RNA virus which has wide antigenic characteristics. It has 3 major types, these are A, B and C. Mostly outbreaks and epidemics are caused by type A and type B whereas type C causes sporadic mild respiratory signs and symptoms. The virus has a filamentous or spherical shape and is enclosed within an envelope which consists of glycoproteins and RNA gene which is single-stranded (Fodor, 2013). Type A of influenza has the potential to bring about periodic changes in themselves such as alterations in their glycoproteins, neuraminidase and hemagglutinin. High level of changes in these type of proteins are known as antigenic shifts and low level are known as antigenic drifts. Pandemic and epidemic caused by influenza are linked to antigenic shifts whereas localized outbreaks are associated with antigenic drifts (Moghadami, 2017; Fodor, 2013).
Influenza virus generally replicates in human's respiratory epithelium. Other cells like immune cells of the body can also be affected by this virus and will start to produce viral protein. However, the efficiency of replication is different among different cell types. In respiratory epithelium, hemagglutinin is cleaved effectively which generates more particles of the virus. This virus primarily causes inflammation in the lungs. The inflammation usually spread systematically and can cause multiorgan failure and therefore can be the reason for severe distress in the respiratory pathway (Kalil& Thomas, 2019).
There can be various implication of influenza on public health. The most common and important is pneumonia. It can happen in people due to prolong acute influenza syndrome which is caused due to influenza virus or a combined reaction of bacterial and viral infection happen just after a few days break. Other implications can be because of the effect that the virus exerts on other systems of the body like cardiac, neurological and musculoskeletal systems. Pericarditis and myocardititus can also happen to individuals in the pandemic or seasonal flu. Also, people have reported cases about rhabdomyolysis and myositis during seasonal influenza. In addition to all of this, there are rare cases of Guillain-Barre syndrome, acute liver failure, Reye syndrome and encephalitis (Moghadami, 2017; Žilinskaitė&Grinevičiūtė, 2020).
Influenza has an incubation time of 1-2 days and then it starts to show the signs and symptoms. These symptoms can be having the sensation of fever, headache, malaise, true chills, severe myalgia and anorexia. Most prominent features are generally headache and fever which helps in recognizing the severity of the illness. The calf muscles are largely impacted by myalgia. With that, people also experience the movement of the eye very painful. The other signs and symptoms are dry cough, sore throat and nasal discharge. However, some symptoms match with common cold too. Patients suffering from influenza experience high-grade fever on the 2-3 day but the fever decrease with time. It usually lasts for 4-8 days. In the initial days, the patient also suffers from red and watery eyes too (Moghadami, 2017; Rao, Chen, Dong, Zhu & Yan, 2020).
Clinical manifestation helps in diagnosing of influenza and there is not much need for laboratory testing. However, in special conditions, there is a need to test the flu and to confirm it via laboratory testing. In the laboratory, the nucleic test can be performed which involves polymerase chain reaction or virus isolation method or rapid diagnosis kits (Moghadami, 2017). Rapid diagnosis influenza tests generally identify the viral antigens of influenza and it screen diseased individuals with suspected influenza in a routine manner. The most used technique for detection with the help of viral antigens is to check the respiratory secretion generated by the patients with the use of immunological methods. Rapid tests are performed by very much ease and give results in only 30 minutes. However, not every test can distinguish between type A and type B influenza. Some tests can also not detect the specific type of influenza A that is whether the infection is caused by H3N2 or H1N1 (Moghadami, 2017). Molecular assays have been used as a gold diagnostic method to detect influenza virus in the laboratories which are hospital-based. These methods are generally polymerase chain reaction-based. Molecular assays have the capability to check multiple targets at the same time and also the subtype and type of the influenza virus which has caused the disease. They also acquire the ability to detect novel targets. The polymerase chain reaction is very sensitive when compared to cell culture-based systems and it can also recognizes nonviable viruses existing in the samples. The higher amount of sensitivity can be gained in these tests if swab samples are acquired (Moghadami, 2017; Nshimyumukiza et al., 2016; Tang et al., 2013).
In the case of influenza, there are four antiviral drugs present for the treatment of influenza. People who are suffering from influenza and it has been confirmed by the laboratory should take the medicines within 2 days of the onset (Moghadami, 2017). Anti-viral medicines should also be taken by the people who are very much suspected of having a viral infection. These medicines should also be taken by patients who can develop complications in having influenza and also when their conditions are not improving (Moghadami, 2017). During the previous wave of the influenza pandemic, neuraminidase inhibitors like zanamivir and seltamivir were prescribed heavily to the patients who were suffering from H1N1 infection (Moghadami, 2017). However, the susceptibility of the influenza virus changes with the medications very rapidly. For the healthcare professionals have to be aware of the patterns shown by influenza in particular seasons and should also know about influenza's susceptibilities and circulation in the local. Some studies have proved that treatment with neuraminidase inhibitors has lessened the mortality rate in the patients. However, there is still less number of therapeutic options available for the treatment of influenza virus. Researches are going on for the innovation of more techniques. One such method which is in the trial phase is mAbs against the proteins of the influenza virus. mAbs generally targets the outermost portions of the virus particles (Moghadami, 2017; Bonmarin et al., 2014; Gasparini et al., 2014).
Prevention from influenza can be done by the vaccination process. This virus has a high rate of mutation and that's why the vaccines are made annually to function against new variants. The procedure of selecting the antigen of influenza which will be included in the vaccine is based on the surveillance performed globally so as to determine novel strains of the viruses in the world (Moghadami, 2017). For the season of influenza in the southern hemisphere, it is recommended that vaccine should be made and given in the month of September and in the northern hemisphere, it should be made available in November. The World Health Organization, 2020, emphasizes the fact that vaccination should be done primarily in individuals who can have severe complications due to influenza and to the women who are pregnant. It should also be given to the patients who are high risk because of their underlying chronic diseases such as diabetes mellitus or renal failure (Moghadami, 2017; Ang et al., 2016; Zhao et al., 2015).
In conclusion, it can be said that the influenza virus is a deadly virus and has caused a lot of deaths worldwide. But looking at the data for the year 2020, a low number of cases has been reported all over the world and also in Australia. It has generally three types, they are type A, type B and type C. Type A and B have cause epidemic whereas type C causes seasonal outbreaks. It is made of RNA and is enclosed within an envelope. It is transmitted by coming in contact with the droplets which have been emitted out by diseased individual by sneezing or coughing. The major populations who are at risk are the ones who have already chronic diseases or the women who are pregnant. Influenza virus targets the epithelium tissues of the respiratory tract. It mainly affects the upper respiratory tract of humans. The signs and symptoms of influenza are fever, headache, malaise, true chills and so on. Diagnosis can be done via molecular tests and rapid influenza diagnostic testing. For the treatment purpose, medicines can be given and also for preventive measures immunization can be done.
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