What are the major influenza infections in humans?

The WHO has classified flu as seasonal, pandemic and zoonotic influenza. The pandemic influenza occurs when new virus emerges to which people lack immunity thus causing huge infections globally (Biggerstaff et al., 2014). These viruses emerge and circulate causing infections outside the normal influenza season. The pandemics may cause severe or mild infections to larger population since majority lack immunity as in Spanish Flu of 1918-19 and subsequent pandemics in 1957 and 1968. The new type A virus known as influenza A(H1N1) emerged and spread around the world in 2009 causing pandemic that was named 2009 H1N1 pandemic. The global occurnece of influenza A(H1N1) is show in figure 1. Since then, no pandemics has been reported.

Figure 1: Global presence of new influenza virus A (H1N1),

Figure 1: Global presence of new influenza virus A (H1N1),


Seasonal influenza cause human disease in certain period of time; in temperate countries, the flu occurs in winter. The three grouping of seasonal influenza is Type A, B and C. The major concern relating to influenza virus is its ability to evolve at a faster rate causing individuals to multiple infections during their life time. The subtypes of Influenza A are A(H1N1) and A(H3N2) named according to specific variety and the protein on their surfaces. ‘H’ denotes for proteins hemagglutinin whereas ‘N” for protein neuraminidase as shown in Figure 2. Influenza A(H1N1) caused influenza pandemic in 2009. The two subtypes of type B flu virus were named according to the places they were first identified hence Yamagata and Victoria lineage (Biggerstaff et al., 2014). Type A and B viruses fatal causing huge disease burned globally.

Figure 2: structure of influenza virion,

Figure 2: structure of influenza virion.The zoonotic influenza also known as variant influenza arises from viruses circulating in animals that cause infections to humans. The common zoonotic influenza viruses are the swine influenza virus (subtype A H5N1 & H9N2) and avian influenza (subtype A H1N1 & H3N2). These viruses rarely infect humans and their infection causes mild to severe pneumonia or even death.

Why flu is a major concern?

Influenza also known as flu is a respiratory illness that is highly contagious caused by virus and spread through sneezing and coughs of infected patient. The virus infect throat, nose and lungs causing mild to severe illness that lead to death in some instances. Huge medical complications associated with flu have been reported such as ear infections, congestive heart failure, diabetes, bacterial pneumonia, sinus infections and asthma (CDC, 2018). Furthermore, approximately 20% of total world population will develop flu though the frequency varies from one region of the globe to another. According to Nordqvist (2017), it is estimated that between 250 and 500 thousand people die annually as a result of flu. A flu epidemic can persist for several weeks when there is large outbreak in a given country causing strain on medical resources. Furthermore, the influenza virus is highly mutative giving rise to drug resistant trains. Various virus types, subtype and lineage has been reported globally including influenza A, A (H1N1), A(H3N2), influenza B, Yamagata and Victoria lineage. Type C influenza causes mild infections.

The clinical symptoms of influenza

According to CDC, the flu symptoms tend to vary from one person to another, however, the most common symptoms include fever, chills, sore throat, muscle aches, fatigue, diarrhea, cough, runny nose, headaches, body aches and vomiting (Belshe, 2005). However, it is important to note that children depict severe symptoms of flu such as vomiting and diarrhea. The people who are at high risk of influenza are the children, pregnant women, elder above 65 years and patients with certain chronic medical conditions. Though many people tend to recover from flu in less than 2 weeks, a significant population may experience serious complications in the lungs due to viral infection necessitating need for urgent medical attention.

During the 1918 pandemic, the patients with influenza reported complaints such as body aches, headache, joint pain, sore throat and harsh breathing. The onset of pandemic was sudden since people were struck with dizziness and weakness that led to sneezing following establishment of the disease. In some patients, cases of hemorrhage of mucous membrane causes bloody nose. The most danger part of influenza infection is its tendency to progress into pneumonia due to secondary bacterial infection (Hsieh et al., 2006).

The secondary complications associated with influenza is therefore deadly especially among children if urgent medical attention is not sought. Though the symptoms described above are clear indication of flu, new diagnostic techniques have been developed to describe the clinical appearance of the disease. Temperature, pulse rate and respiration rate are usually monitored to provide clues of clinical progression of flu infection. Modern diagnostic tools that are also in use involve chest x-ray, analysis of stool, analysis of blood for antibodies and urine analysis to measure albumin since albuminuria is common among influenza patients (Jhung et al., 2011).

Etiology of flu

There has been rapid development in medical researches that has shaped public health through medical responses. The great work of Koch and Pasteur has helped unraveled infectious diseases through the germ theory of disease that links disease to a given specific microbial agent. As a result, various viruses, fungi and bacteria has been characterized and slinked to various specific disease. Influenza is one of the pandemic diseases caused by influenza virus. The deadly 1918 flu estimated to kill around 100 million people generated a lot of interest for many scientists around the globe. Following 1890 influenza pandemic, Pfeiffer was able to determine the bacteria Bacillus influenza as causative agent of bacteria (Eyler, 2010). Identification of the microbial agent is attributed to use of petri dishes to grow and investigate cultures of bacteria. However, many studies conducted between 1907 and 1910 gave conflicting ideas about true causative agent of flu. Some scientist found Bacillus in 15% of patients suffering from flu. Furthermore, bacillus was present in other cases of diseases such Tb, chronic bronchitis, scarlet fever and the measles, similarly Rosenthal found that 16% of healthy patients had Bacillus thus refuting claims that Bacillus causes flu (Eyler, 2010).

The 1918-19 flu pandemic offered great drive for scientist to find the etiological agent responsible for the deadly disease. As a result, it is reported that great studies was conducted in various laboratories using the cultures provided by physicians handling flu patients to help in isolating etiological agent for the flu. There was a great dilemma whether the disease was as a result of new bacteria, virus or unidentified microbe. Though the concept of was virology was known phenomenon, few scientists thought of virus as causative agent of flu. The earliest experiments conducted by the Nicolle and Bailly in France suggested that flu was caused by virus (Pham et al., 2013). The two scientists conducted an experiment where they obtained bronchial expectorations and subjected it to filtration to ensure that it was free of bacteria before injecting the filtrate into the monkeys. Interestingly, the monkeys developed fever; similarly, the volunteer individuals who were injected the filtrate also developed the typical sign of flu. This study proved that flu was caused by virus and not bacteria as initially postulated by Pfeiffer. The advancing virology thus helped in identify the causative agent of flu as the influenza virus.

What are the treatment options  and therapy of flu?

There is varied therapeutic remedies for flu from one country to another ranging from use of oils to drugs and herbs. Early in the 18th century, the treatment of the flu was less scientific since it majored on relieving symptoms such as fever or pain. As a result, aspirin was a common remedy for pain and fever among the flu patients. Furthermore, the oil or powder derived from cinnamon was also a popular remedy for reducing temperatures. Several strategies were used for treating flu patients in 1918 including use of quinine, patients given plenty of nourishment and fluids and cooling the head. All these strategies just minimized symptoms since it had low efficacy in treating the disease. As a result of understanding etiology of flu, modern medical therapies have been described to deal with the disease.

The earliest scientists to incorporate scientific ideas in treatment flu were O’Malley and Hartman who proposed the use of theorized antibodies to boost immunity of patients. Currently there are numerous antiviral drugs for treating flu illness such as osetamivir, peramivir and zanamivir. The antiviral drugs are taken only after prescription by the doctor and exist in various forms such as liquid, powerder, pills and intravenous solution. People at high risk of serious influenza complication are advised to check doctor promptly. The antiviral drugs are effective in treating flu since they act faster in lessening symptoms thus reducing the risk of pneumonia, hospitalization or even death especially when administered early. The flu antiviral drugs are known to work best when administered within 2 days of infection. However, side effects of antiviral drugs that are common include nausea and vomiting.

Current medical advances

There are great medical advances since 1918 that has helped contain the disease. The antibiotics, vaccines and ventilators currently in used has increased patient’s ability to survive flu infection. Though antiviral drugs are effective in treating flu, it is important to get vaccines as the best strategy for preventing seasonal flu. The vaccine is usually administered every year to get best protection. The are two types of vaccines commonly in use against flue; the flu shot vaccine administered with needle for people over six months in the arm and the nasal-spray vaccine given as live attenuated virus that does not cause illness (Hsieh et al., 2006). Due to increased resistance, the vaccines are made to contain three major viruses that is influenza H1N2, H3N2 and B virus. These vaccines are known to offer efficient protection after two weeks of administration.


Belshe, R.B., 2005. The origins of pandemic influenza—lessons from the 1918 virus. New England Journal of Medicine353(21), pp.2209-2211.

Biggerstaff, M., Cauchemez, S., Reed, C., Gambhir, M. and Finelli, L., 2014. Estimates of the reproduction number for seasonal, pandemic, and zoonotic influenza: a systematic review of the literature. BMC infectious diseases14(1), p.480.

CDC, 2018, Key Facts About Influenza (Flu). Retrieved on May 1, 2018 from

Eyler, J.M., 2010. The state of science, microbiology, and vaccines circa 1918. Public Health Reports125(3_suppl), pp.27-36.

Hsieh, Y.C., Wu, T.Z., Liu, D.P., Shao, P.L., Chang, L.Y., Lu, C.Y., Lee, C.Y., Huang, F.Y. and Huang, L.M., 2006. Influenza pandemics: past, present and future. Journal of the Formosan Medical Association105(1), pp.1-6.

Jhung, M.A., Swerdlow, D., Olsen, S.J., Jernigan, D., Biggerstaff, M., Kamimoto, L., Kniss, K., Reed, C., Fry, A., Brammer, L. and Gindler, J., 2011. Epidemiology of 2009 pandemic influenza A (H1N1) in the United States. Clinical Infectious Diseases52(suppl_1), pp.S13-S26.

Nordqvist, C., 2017, All you need to know about flu. Retrieved on May 1, 2018 from

Pham, T., Combes, A., Rozé, H., Chevret, S., Mercat, A., Roch, A., Mourvillier, B., Ara-Somohano, C., Bastien, O., Zogheib, E. and Clavel, M., 2013. Extracorporeal membrane oxygenation for pandemic influenza A (H1N1)–induced acute respiratory distress syndrome: a cohort study and propensity-matched analysis. American journal of respiratory and critical care medicine187(3), pp.276-285.