Rotavirus and Colorado Tick Fever Virus – Reoviruses

by Sean Elliott, MD

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    00:01 The reoviridae, viruses.

    00:04 The reoviridae are medium-sized, nonenveloped, double-icosahedral capsids.

    00:11 And they are interesting because they have a segmented, double-stranded RNA genome, meaning they have both a positive and a negative-sense RNA strand in their genome.

    00:22 he medically relevant reoviridae viruses are rotavirus, quite a common cause of severe gastroenteritis.

    00:30 And then, less commonly, the Colorado tick fever virus.

    00:34 We can see in the image on the screen a electron micrograph of reo -- in fact, in this case, rotavirus particles, and they look nice and uniform, very pleasant-speaking, until you get sick from them, in which case we're very sad indeed.

    00:50 Pathogenesis of rotavirus, looking specifically at that one now.

    00:54 The virions, partially digested, come through the stomach, where they are partially acid susceptible, but still infectious.

    01:05 nd if they are still infectious, they can directly penetrate the intestinal epithelial cells.

    01:11 There, as they start to replicate, etc., they do several things.

    01:17 One is to secrete a cholera toxin-like protein.

    01:20 And again, the virus doesn't secrete that, but it has a genome, which when transcribed, creates a protein which does these functions.

    01:29 And this cholera toxin protein allows destruction of the villous absorption, so the villi at the surface of that intestinal epithelial cell are destroyed.

    01:41 and they're unable to absorb electrons such as sodium, potassium, which means that water passage does not occur.

    01:50 So, one already has a water loss diarrhea, but at the same time, the act of the rotavirus replicating itself also encodes proteins to increase the proliferation or metabolic machinery of that intestinal epithelial cell.

    02:10 So the cell, in addition to losing water, hypersecretes water.

    02:16 So, rotavirus diarrhea is unusual because it is both a secretory diarrhea, and a malabsorption diarrhea.

    02:25 You get a sense that maybe there's a lot of water loss going on.

    02:29 So, in the diarrhea, when it's occurring, again, both mechanisms for losing water, one is also, of course, shedding tons of virions because these are the viruses being produced by those now ruined intestinal epithelial cells.

    02:44 That means that rotavirus diarrhea is incredibly contagious.

    02:49 Even a small amount can transmit new disease to somebody else.

    02:54 Thus, rotavirus diarrhea occurs in many epidemics every year throughout, especially closed communities, daycares, schools, you name it.

    03:05 It's a very big deal.

    03:08 The immunity derives, again, from those partially digested virions in which, as they're binding to the intestinal epithelial cells, an immunoglobulin A or a mucosal humoral or antibody reaction is occurring, and that starts to derive immunity.

    03:25 However, there are several different serotypes of rotavirus, so in fact, one could get rotavirus several times in one's childhood life.

    03:34 So, what does the disease look like? Well, the incubation period is about 48 hours Transmission, as you've already figured out, is fecal-oral.

    03:43 And the clinical manifestations are incredibly watery diarrhea, some vomiting, low-grade fevers lasting for 4-5 days.

    03:52 The principal problem, because of that water loss, then is dehydration; not gut disruption, but water loss.

    04:00 As an FYI, because my daughter also had rotavirus when she was young, this is an incredibly foul-smelling, green diarrhea.

    04:10 It's just not pleasant to look at at all.

    04:12 And unfortunately, in changing all those diapers, you will look at it a lot.

    04:17 Severity.

    04:19 Almost all patients have a self-limited disease, unless they have some underlying, you know, deficiency.

    04:25 Complete recovery is common, in fact, almost uniform.

    04:29 However, some patients, especially those who are already malnourished or already have underlying gut distress, may develop very severe water loss and they may die from complications of the rotavirus infection.

    04:44 Most children however, and certainly adults if they are are unlucky enough to acquire this, will have, in relative sense, a mild diarrhea, meaning it only lasts 4-5 days.

    04:56 Older children also, and adults, are starting to develop some immunoglobulin A immunity, and so, even if they were not vaccinated, they might actually develop less severe disease because their enterocytes are partially protected.

    05:13 To identify rotavirus, one could look for viral antigens or the virions in the stool, and both a serologic assay exists, as do molecular diagnostics.

    05:24 Prevention, thankfully, now, comes from an attenuated rotavirus vaccine, which when initially created and released, was associated potentially causally with an increased risk of intussusception.

    05:39 Thankfully, a new viral product, antiviral product has come out, 2 vaccines, which, so far, have demonstrated only a mild increase in potentially related intussusception.

    05:51 So, prevention, of course, is the best treatment, but those patients who still get rotavirus will require extensive fluid replacement therapy, starting with oral rehydration therapy, but sometimes, progressing to intravenous therapy.

    06:05 So, the second virus in this category, not to completely ignore it but is the Colorado tick fever virus.

    06:12 And as you imagine, given the name, this is a vector-associated infection.

    06:18 Incubation period is typically 3-6 days after exposure.

    06:23 The vector is the Western or Northwestern wood tick and thus, you might expose yourself to this infection if traveling, hiking, camping, etc., in those parts of the States and Canada.

    06:38 The infection itself is biphasic, meaning that the initial fever, chills, head= ache, viral sensitivity, viral syndrome occurs, there's a period of sometimes 3 to almost 7 days where the patient is feeling better, thinking, "Ha ha, phew. Dodged that bullet," and then they get sick again with the same thing.

    06:59 The full manifestations of Colorado tick fever are severe fever with rigors, chills, bad headaches, which are typically both frontal and temporal, light sensitivity, photo sensitivity, diffuse myalgias.

    07:13 They feel horrible, just generally lie in bed with malaise, and patients may develop gastrointestinal complications with hepatosplenomegaly, nausea, vomiting, occasionally some mild diarrhea.

    07:26 And there occasionally is a rash, which when noted, is flat, erythematous, and macular.

    07:31 It's a very nonspecific rash, unlike some of the other tick-associated infections that we've talked about.

    07:38 The infection itself is self-limited, so at the end of 2 weeks, patients will have recovered from their second part of the biphasic illness.

    07:47 So, in thinking about Colorado tick fever virus, the key to remember here is that it occurs in 2 parts as a biphasic tick-associated illness.

    07:57 And thinking about the rotavirus, remember, it's ubiquitous, it'd quite a significant diarrhea, and the diarrhea is both osmotic and secretory together.

    08:08 To treat rotavirus, prevent it with vaccine, and give lots of fluids, and watch out for those diapers.

    About the Lecture

    The lecture Rotavirus and Colorado Tick Fever Virus – Reoviruses by Sean Elliott, MD is from the course Viruses.

    Included Quiz Questions

    1. Segmented, double-stranded RNA
    2. Segmented, single-stranded RNA
    3. Segmented, single-stranded DNA
    4. Segmented, double-stranded DNA
    5. Circular, double-stranded DNA
    1. ...48 hours.
    2. ...24 hours.
    3. ...36 hours.
    4. ...60 hours.
    5. ...72 hours.
    1. Cholera toxin-like protein
    2. Shiga toxin-like protein
    3. Campylobacter toxin-like protein
    4. Clostridium toxin-like protein
    5. Cryptosporidium toxin-like protein
    1. IgA
    2. IgG
    3. IgD
    4. IgE
    5. IgM

    Author of lecture Rotavirus and Colorado Tick Fever Virus – Reoviruses

     Sean Elliott, MD

    Sean Elliott, MD

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