Thursday, November 24, 2005

Virology: A primer on Viruses and "Bird Flu"

I have recently recieved several questions concerning Viruses in general and the Bird Flu in particular so I thought I would give a short tutorial on the subject. If it's to in depth....sorry, I have a habit of doing that.
More in depth info can be found HERE.
One way to think of viruses in very small microscopic machines that have the ability to invade your cells, reproduce within them and then exit in mass numbers to infect other cells. If you picture this happening you can see why you feel so bad as this is happening. Once a virus gains access to the body (usually through the respiratory system) it attaches to the surface of the respiratory epithelium ( via the "H" protein, Hemaglutinin) and then inserts itself or is absorbed by endocytosis (cellular engulfing). Once within the cell, the virus begins replication protected from attack by the immune system. Once a significant number (crital mass) of viral particles is obtained within the cell, they are expelled (via "N" protein, Neuraminadase) and the process is repeated again. The bodies immune system is in a virtual race with the virus as anti-bodies are produced to the surface proteins and replicated for distribution throughout the body as a defense against the rapidly spreading infection. As you can imagine, if you have never been exposed to a virus before them the immune system is at a significant disadvantage and lags way behind the shear number of viruses produced. If the immune system can't get the upper hand in this fight then you lose to many respiratory cells and you can no longer over. From this you can see why there is such interest in the current "bird flu" and the recent human to human transfer everyone has feared (New Scientist breaking news)Here is a chart on the basic facts about the Orthomyxoviruses of which Influenza is a member.

ORTHOMYXOVIRIDAE: The Influenza Viruses

  • STRUCTURE: ss (-) RNA, segmented, helical nucleocapsid, enveloped.
    • Cell envelope is acquired by budding through plasma membrane.
    • Hemagglutinin (HA) on viral envelope attaches to sialic acid receptor on host cells. One source of antigenic types.
      • There are 15 subtypes of HA. H1, H2, H3 exist in humans.
    • Neuraminidase (NA) is released from infected cells. Another source of antigenic types.
      • There are 9 subtypes of NA. Only N1, N2 are found in humans.
  • REPLICATION: In host nucleus. Cap-snatching transcription. Viral RNA's utilize portions of host-cell RNA to make their own 5' Cap in the host cell nucleus.
    • Antigenic Shift: Major source of antigenic variation, due to re-assortment of the RNA genome segments. It leads to changes of subtype of the envelope glycoproteins.
    • Antigenic Drift: Minor changes in antigenic variation, due to point mutations in the genome.
  • INFLUENZA VIRUS-A: 8 segments.
    • DISTRIBUTION: Found in humans, aquatic birds, swine, horses, seals, whales.
    • EPIDEMIOLOGY: This is the major player in flu epidemics, because of its antigenic variation. Highly contagious, spread by person-to-person contact.
    • MANIFESTATIONS: It targets the epithelial cells of the respiratory tract, upper and lower.
      • Epithelial cells become ciliastatic as a result of infection, which can predispose to more serious bacterial infections.
      • Incubation Period: 1-4 days.
      • Symptoms: Soar throat, fever, chills, myalgia, headache.
      • Normally Self-Limiting infection, lasting 3-7 days. Cough may last 1-2 weeks.
  • INFLUENZA VIRUS-B: 8 segments
    • DISTRIBUTION: Found only in humans
    • EPIDEMIOLOGY: Less serious infection than Type-A. Generally found in children or adolescents.
    • Influenza-B does not undergo reassortments or antigenic shift.
  • INFLUENZA VIRUS-C: 7 segments.
    • DISTRIBUTION: Found in humans and swine.
    • EPIDEMIOLOGY: Rarely causes diseases. Ubiquitous, and we all generally have antibodies by early childhood.
  • INFLUENZA VACCINE: Constantly updated, as CDC keeps track of antigenic types of latest strains.
    • In the past they've used inactivated whole viruses.
    • This year they are using a trivalent subunit vaccine consisting of purified viral HA antigen: (1) Type-A H1N1 and (2) H3N2, and Type-B antigen.
    • Vaccine administered during the fall. Breakouts are in winter.

Sunday, November 20, 2005

Cushings Disease...."does this halter make me look fat ?"

As horses live longer we have to deal with the everymore likely possibility of "cancer".
One of these is a small tumor on the Pituitary gland at the base of the brain. The Pituitary gland is responsible for regulation of Hormone production in the body and as tumors develop they cause an abnormal production of these substances. In the Horse this frequently leads to "Cushings Disease" and a wide array of clinical signs such as Laminitis, a long curly hair coat and excessive drinking. The big problem is the laminitis and hoof abcesses which can spell disaster for your horse, the key is picking up the problem early. To do this we do an extensive physical exam to see if this could actually be Metabolic syndrome (another problem) and then do diagnostic testing for organ function and a dexamethasone suppression test. While the tumor itself is not treatable at this point there are medications we can use to control the clinical signs. Primarily we use Cyproheptidine and Pergolide . The cost of treatment is usually less than $60 dollars a month and can keep your horse is reasonably good health for years to come. Stay alert for any of these symptoms in your horse and watch for the wavy hair that doesn't shed out in the summer.

Tuesday, November 15, 2005

Equine Influenza, Greyhounds and Bird Flu.

Things seem to be heating up on the Bird Flu front ( Great Britain) and (China) and it makes you wonder about the development of persistent cross species transfer. There has recently been a similar event seen in Florida where Equine Influenza has been linked to an outbreak of respiratory disease in Greyhounds ( here ). As is the concern in people with Bird Flu, the Greyhounds had no immunity to this virus, and it was severe. When there is no antibody response to an infection it replicates unchecked through the body damaging any system it is geared to. Influenza is primarily a respiratory virus and replicates in bronchial and alveolar epithelium. When these cells are infected they become swollen and leak cellular fluid and eventually slough into the airway. This causes reduced oxygen exchange and excess fluid in the lungs making breathing difficult. Those that die essentially drown. Not a pretty picture. There have been cases where the current Bird flu
has been transfered to yet another species (cats and pigs ). With the current spread of the virus through Asia, it is reasonable to assume that ferrel cats could work as another vector if there eat infected wild birds. We currently know the virus can infect humans but as of yet no human to human transfer has developed. With these early signs of inter-species transfer we will have to watch closely for signs of human to human spread. This will most likely show up as a village
epidemic either in Asia or Africa.

Tuesday, November 08, 2005

Update: Horse stabbing......CSI -Equine

Curiouser and curiouser. The story about the stabbed horse has legs (sorry bout the pun).
I had a call from the sister in law last night "I think I just saw your stabbed horse on the news". Yup, there he living color , on the 11:00 news. Now, I don't want to down play the significance of the injury but we are rapidly approaching media saturation with an article on the front page of the Metro section in todays paper and another segment on the evening news tonight.
The local station even had a link to a site about the incident that stated that the bills could run as high as $15,000 and could make donations ( NOTE-this wasn't my site). I've looked at my bill and I'm still not sure how you get to that figure. I'm just waiting on the call from Geraldo....... or my attorney.

Monday, November 07, 2005

"Somebody Stabbed my horse!"

Let me start out by saying that this was a new one. I'm never surprized by what some people do to animals (such as HERE ) and I've seen plenty. Like the time someone shot their horse for getting into the garbage, honest I saw it. "I was just tryin' to scare him", sure you were, just tell that to the officer. But last night I got the "stabbed" call. The owner had riden the horse up to the local convienence store and while inside....the deed was done. The horse was tied to a tree and had blood pouring from a wound in the center of the chest while someone(we'll call him the Perp) was running away. It's never a good sign when you arrive to treat an animal and there is a significant police presence, but I did feel better with a "horse-stabber" on the loose. After an exam which revealed a DEEEEP hole in the left pectoral muscle and alot of subcutaneous emphysema (air under the skin along the left side of the body). The good thing was that it did not appear to penetrate the chest cavity. It's said in trauma circles that "chest wounds suck"...for alot of reasons.I couldn't find any sucking sounds around the wound. After packing the wound and closing the skin he was treated with antibiotics and moved to a stall. I wanted to have the horse hospitalized but the owner couldn't get the horse transported. Not sure what actually caused it since I wasn't there so I can't say whether it was accidental or a malicious event, either way the horse was doing OK. After we were finished I said my goodbyes and went to shake hands with the officer in charge " you don't have any blood on your hands do you, doesn't look good for a cop to have blood on their hands". I guess the "detective" didn't notice the clue that I had been wearing surgical gloves. Hmmmmmm.

Tuesday, November 01, 2005

Bird Flu ?

In case you didn't know I also have a degree in Microbiology which is why I'm interested in topics like the current "bird flu" scare. Here are some need to know facts 1. It's not in the USA 2. It has not shown an ability to transmit from human to human 3. It can't infect your horse or you....yet. You can find more on this here and here.
What you see in the news is a discription of the virus as H & N numbers. This is related to surface makers H= hemagglutinin ( 16 subtypes) and N= neuraminidase(9 subtypes), this one is classified as H5N1. This flu infects birds and has spread to humans working with them in about 160 cases in asia. Of these cases about 40% were fatal, making it a serious world health risk. The buzz word is "pandemic", which is a new disease that spreads from person to person. There have been 3 pandemics in the last 100 years , the first being the flu outbreak at the turn of the last century(1918)and most recently in 1968. The concern is that this virus will spread as the birds migrate towards Africa where a significant number of people suffer from AIDS and have a weakened immune system. This provides an environment where the virus can come in contact with others and could mutate into a form that can spread by direct human contact.
The current thought is that should this happen it could be in the US within two months. Hmmmmmm, makes you think. The reason this would be so devastating is that the human immune system has never seen this virus before and has no antibodies directed against it.....
it would be like having AIDS or having had chemotherapy and getting the flu. There would be nothing in your body to stop it. So where do we go from here. Right now it is just wait and see as to what the virus does over the next few years ( you'll hear about it again). The stock piling of drugs such as Tamiflu isn't warranted at this point and the current flu shot won't help ( although it is still a good idea for other reasons). This has the potential to be real bad, but there have always been bugs like this out there and we never heard about them until the 24 hour news cycle, the difference now is the amount of global travel and how fast one can spread around the world. Keep your eyes open for changes and keep reading. I've always thought that it wouldn't be man's violence or stupidity that would do us would be the BUGS.