Orthomyxoviridae

Presented by: Dr. Faghihloo The family Orthomyxoviridae Schematic diagram of particles Influenza virus replication cycle Clinical Features • Adults • Infection with influenza A results in clinical responses ranging from asymptomatic infection to primary viral that rapidly progresses to a fatal outcome.

• The typical uncomplicated influenza syndrome is a bronchitis with some involvement of small airways. The incubation period ranges from 1 to 5 days.

• Physical findings in influenza are confined to the respiratory tract. Nasal obstruction, , sneezing, and pharyngeal inflammation without exudate are common. Clinical Features • Children • The clinical manifestations of influenza in children are similar to those in adults, but there are some distinct differences.

• There is a proportionally greater burden of illness in children than in adults. Children have higher that may be accompanied by febrile convulsions.

• , , pneumonia, and myositis are more frequent in children than in adults Clinical Features

• Lower Respiratory Tract Complications • Three distinct syndromes of severe pneumonia can follow influenza infection in children or adults. Complications are most common in the elderly.

• Primary • Primary viral pneumonia occurs predominantly in individuals at high risk for the complications of influenza virus infection (i.e., the elderly or patients with cardiopulmonary disease) , but 250/o of cases are in individuals without risk factors and an additional 130/o are in pregnant women. Clinical Features

• Combined Viral-Bacterial Pneumonia

• Combined viral-bacterial pneumonia is quite common. The bacteria most often involved are Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae, although other micro-organisms can play a role.

• Clinically, this syndrome may be indistinguishable from primary viral pneumonia, except that the symptoms of pneumonia appear somewhat after the influenza symptoms and chest radiographs are more likely to show pleural effusions. Clinical Features

• Secondary Bacterial Pneumonia

• In this syndrome, an individual recovering from a typical influenza illness develops shaking chills, pleuritic chest pain, and an increase in productive of bloody or purulent sputum.

• Cyanosis and a marked increase in respiratory rate are less common than with primary viral pneumonia. Extra pulmonary Manifestations

• Viremia • Viremia is highly unusual in influenza virus infections. Virus was isolated from the at low levels (present only in undiluted blood specimens) from a patient on the fourth day of influenza illness.

• Myositis • In adults, a diffuse myositis can occur with generalized pain, tenderness, and of muscles, increased serum levels of muscle , myoglobinemia, and myoglobinuria. Extra pulmonary Manifestations

• Cardiac Involvement

• Influenza recovery from the heart of patients with myocarditis associated with fatal pulmonary infection is rare.

• Clinical findings and cardiac function studies in patients with severe pulmonary infection suggest that myocardial dysfunction is not a direct result of infection. Extra pulmonary Manifestations

• Reye Syndrome

• Reye syndrome is a rapidly progressive no inflammatory encephalopathy and fatty infiltration of the viscera, especially the liver, which results in severe hepatic dysfunction with elevated serum transaminase and ammonia levels.

• This syndrome is seen following respiratory, varicella, and gastrointestinal viral infections. Extra pulmonary Manifestations

• The onset of the central nervous system (CNS) and hepatic symptoms usually begins as respiratory tract symptoms wane.

• The varied between 22°/o and 42°/o.

• Salicylate administration is a critical cofactor in the development of Reye syndrome. Extra pulmonary Manifestations • Central Nervous System Involvement • A wide spectrum of CNS disease has been observed during influenza A and infections in .

• Infection During Pregnancy • Pregnant women in the second or third trimester have an increased risk of developing fatal influenza disease.

• Infection in lmmunosuppressed Patients • Influenza viruses can cause severe disease in immunocompromised individuals Antivirals

• Four antiviral compounds the M2 ion channel inhibitors and , and the inhibitors and are currently approved in many countries for use in humans.

• Additional neuraminidase inhibitors such as and received temporary emergency approval during the HlNl pandemic in 2009, and/ or are licensed in Japan and Korea. Vaccines

• Vaccination is one of the most effective methods for preventing influenza virus infections and complications.

• Both inactivated and live attenuated vaccines are available against seasonal influenza viruses. Vaccines

• These vaccines are currently trivalent, that is, they contain influenza A virus components of the H1N1 and H3N2 subtypes, and an component.

• Trivalent inactivated vaccines can be used for persons older than 6 months of age, while live attenuated vaccine is currently approved in the United States for healthy, non pregnant individuals 2 to 49 years of age. Flu vaccine 2019-2020

• Flu vaccines are updated to better match viruses expected to be circulating in the United States. The A(H1N1)pdm09 vaccine component was updated from an A/Michigan/45/2015 (H1N1)pdm09-like virus to an A/Brisbane/02/2018 (H1N1)pdm09- like virus.

• The A(H3N2) vaccine component was updated from an A/Singapore/INFIMH-16- 0019/2016 A(H3N2)-like virus to an A/Kansas/14/2017 (H3N2)-like virus.

• Both B/Victoria and B/Yamagata virus components from the 2018-2019 flu vaccine remain the same for the 2019-2020 flu vaccine. Evolution of influenza A circulating in humans