Paramyxoviruses

00:01 The paramyxoviridae viruses.

00:04 The paramyxoviridae are very important viruses.

00:08 They are large, enveloped, with a helical capsule, and they have a linear, single-stranded, negative-sense RNA genome.

00:15 So again, if you remember anything about this particular family of virus, this is a negative-sense RNA virus, which means that it must carry, and it does, its own RNA-dependent RNA polymerase, the RDRP.

00:29 You can see in a transmission electron micrograph in front of you a picture of one of the paramyxoviruses, and it's a very large shaped organism.

00:39 There are many medically relevant species in this family, the paramyxoviridae.

00:44 Measles virus, mumps virus, the human parainfluenza virus, cause of croup.

00:49 Respiratory syncytial virus, a huge cause of bronchiolitis in children, and then the human metapneumovirus, which is very much -- almost like a combination of parainfluenza and respiratory syncytial virus.

01:02 So, a whole bunch of nasties in this particular family.

01:05 So, all of these viruses, the paramyxoviruses, have the same pathogenesis.

01:11 . So they start with a two-step binding process.

01:15 The first is attaching to their target cell via a fusion protein, the F protein.

01:21 And then there's a secondary fusion with the envelope of the virus and the cell membrane of the target cell.

01:29 And then the capsid itself is released into the cell.

01:32 Now, importantly, 1 cell can be be infected with or attacked by multiple of the paramyxoviruses, giving it the appearance of a multinucleated cell.

01:43 It's just a whole bunch of viral capsids inside that cell.

01:48 As that primary infection occurs, it's occurring with the epithelial cells of the upper respiratory tract.

01:55 Kind of makes sense because all these have a respiratory droplet transmission, and so one breathes in the virus, they attack the upper respiratory tract, and one gets these viruses bound to the airway respiratory epithelium.

02:09 In the case of measles and mumps, the first 2 that we'll talk about, there is then a secondary viremic spread, which accounts for the systemic manifestations of those 2 viruses.

02:21 In the case of the parainfluenza, RSV, and human metapneumovirus, there is not a viremia.

02:27 So they account for primarily respiratory symptoms.

02:31 Here, we see an image of a multinucleated cell.

02:36 This is an epithelial cell with the green arrow to make sure you can't miss it.

02:39 But it has multiple capsids, multiple virion capsids inserted into its cytoplasm.

02:46 Now, importantly, this whole family of cells are both sensitive to and inducers of interferon.

02:54 So they almost self-stimulate to create even further impact through the effects of interferon.