Influenza: Etiology and Pathology (Pediatric Nursing)

00:00 Now let's talk about influenza.

00:03 Influenza is a highly contagious, viral, respiratory infection that infects the nose, the throat, and the lungs.

00:11 It's caused by influenza viruses that are common in late autumn to early spring.

00:17 And children younger than 5 years, especially those younger than 2, are at a high risk of serious complications from influenza.

00:27 How do we prevent influenza? Well, vaccination.

00:30 That's the best protection.

00:32 Influenza is an RNA virus with a roughly spherical lipid envelope.

00:37 The outside of the virus capsule is covered with spikes of proteins that are involved in the viral docking, endocytosis, and fusion of the viral membrane to the host cell.

00:47 Here is the N protein or neuraminidase.

00:52 Inside the envelope is the capsid, and that's a protein shell that contains the genetic information of the virus.

00:59 At the core, there are about 8 strands of RNA that are patiently awaiting their release into the host cell.

01:06 The H protein, or the hemagglutinin, is another spiky glycoprotein on the surface that helps it bind with the host cell.

01:14 Influenza is a virus that actually has hundreds of different strains.

01:19 The virus mutates frequently, but the strains are classified into 1 of 3 main categories: A, B, or C.

01:27 Now, influenza C does not cause serious illness, so in this lecture, we're primarily focusing on influenza A and influenza B.

01:34 Influenza A.

01:36 You can remember this.

01:36 That is awful.

01:38 It is responsible for frequent, usually annual, local outbreaks or local epidemics that vary in intensity every 2 to 3 years.

01:47 Then occasionally, it will cause pandemics.

01:50 Influenza A causes more severe symptoms than influenza B or influenza C.

01:55 Influenza A viruses can be broken down into subtypes depending on the genes that makeup the surface proteins.

02:02 Over the course of a flu season, different types, A and B, and the subtypes of influenza A circulate around and cause illness.

02:11 Within the type A influenza viruses, there are subtypes based on their H and N antigens.

02:18 This allows for multiple different combinations or strains that circulate within the community each flu season.

02:25 Antibodies to 1 subtype of H or N antigen do not react with the other type of H or N antigens.

02:31 So, unfortunately, a patient can get sick with multiple strains in the same flu season.

02:38 There are 3 antigenic subtypes of the H antigen: H1, H2, and H3.

02:44 And there are 2 antigenic subtypes of the N antigen: N1 and N2.

02:50 Now we'll talk about the B viruses.

02:52 These are a little bit better.

02:54 You can remember them.

02:55 And the outbreaks happen about every 4 years.

02:59 Patients with influenza type B typically have milder disease than those with influenza type A.

03:05 And the other type, type C, that we're not really going to cover much, doesn't cause serious illness in the general population.

03:13 So here we are with Type A.

03:15 Remember, it's awful and responsible for annual outbreaks.

03:20 All influenza A viruses are further broken down into those H and N subtypes.

03:25 So any influenza virus that's described as an H with a number, and then an N with a number, such as H1N1 or H3N2, is a type of influenza A virus.

03:36 Other combinations have been found to infect other species, such as birds and pigs, but they have not caused widespread human infection.

03:45 There are 16 H subtypes and 9 N subtypes, but only 3 of these combinations have actually caused highly contagious illness in humans.

03:54 The 3 combinations that cause almost all outbreaks of flu in humans are the H1N1, the H2N2, and the H3N2.

04:05 Type B strains, remember, do not cause as severe of symptoms as type A.

04:09 And over on the right, type C, those don't really cause any serious symptoms.

04:15 The influenza virus is transmitted through the spread of infected respiratory droplets that are aerosolized, sprayed out into the air, by coughing, sneezing, or talking.

04:26 It can also be spread with direct contact with fomites, and these are phones, doorknobs, countertops, shopping carts.

04:34 And I find it interesting when patients come in during flu season and they always say, "Where do you think I got the flu?" And, "Where could I have possibly come in contact with the flu?" And my answer is, "It's everywhere." It's in the air of the people around you who are coughing and sneezing and spraying their droplets.

04:51 And then it is settling on to all of the objects in the environment just waiting to be touched by you.

04:57 This is going to enter the patient's tracheal bronchial epithelium, where the virus is going to begin to replicate.

05:05 The patient will shed the most of their virus in the first 48-72 hours after they've contracted the virus, and this is when they may not be feeling super symptomatic.

05:14 These patients are still going to school, they're still going to work, and they are spreading the flu around.

05:20 Patients will be contagious for about 5 days after their symptoms begin.