MicrobiologyBytes

Methicillin-resistant Staphylococcus aureus (MRSA) is usually associated with hospital infections, where it can cause severe illness in the immunocompromised and elderly, particularly people with wounds where the bacteria can get in. In this article in Microbiology Today (pdf) Jodi Lindsay tells us about a novel strain of MRSA found in the USA that is causing concern. Called Community-acquired-MRSA (CA-MRSA), the bacteria can cause infection in healthy people and several outbreaks in contact sports teams have been reported:

Staphylococcus aureus are bacteria that commonly live in the nose, and about 20% of us carry them all the time, with another 50% intermittently coloni-zed. We have all had an S. aureus infection, usually an infected cut or wound that became inflamed and maybe produced some pus. Because of our healthy immune response, predominantly the production of neutrophils, we didn’t need anti-biotics and the infection cleared itself. Very occasionally, a S. aureus infection can become more serious in a healthy person, but we don’t really know why. However, in the USA there have recently been out-breaks of a new type of meticillin-resistant S. aureus (MRSA), to which athletes are particularly vulnerable…

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• MRSA: Methicillin-resistant Staphylococcus aureus
• Novel treatments for MRSA
• Evolution and pathogenesis of Staphylococcus aureus
• Maggots or MRSA?

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1. What is swine flu?
Swine flu is a type of influenza virus. Influenza viruses are named after the proteins on the outside which are recognized by the body, H and N. There are dozens of combinations of these two proteins, each one giving a different type of influenza virus. Swine flu virus is H1N1 influenza. The original swine flu virus was first isolated from a pig in 1930.

2. Can it hurt me?
Influenza viruses infect pigs (swine), birds, humans and a few other species. Most strains of influenza are quite restricted in the host they will infect but occasionally jump from one species to another. Swine flu infects pigs but is also capable of infecting humans.

3. Will there be a swine flu pandemic?
It’s too early to say. Scientists are carefully recording the spread of the current epidemic to see how easily this virus is capable of spreading from person to person. World Health Organization (WHO) Director-General Margaret Chan says the present outbreak “has pandemic potential” but that “it is too early to say whether a pandemic will actually occur”.
Update: This outbreak is now officially a pandemic.

4. How many people have been affected by swine flu?
The number is growing – click here for the latest news.

5. Is there any treatment for swine flu?
Vaccines are available against H1N1 influenza but it is not known how effective they are against this strain. WHO says the virus appears to be susceptible to the influenza drug Tamiflu (oseltamivir), and Relenza (zanamivir). It is not known if resistance to these drugs will occur.

6. How does swine flu spread?
Influenza viruses are transmitted through coughing or sneezing by people infected with the virus. People may become infected by touching something with the virus on it and then touching their mouth or nose, so frequent hand washing is a good idea. You cannot get swine influenza from eating cooked pork or pork products.

7. Has swine flu infected humans before?
Sporadic human infections with swine flu occur regularly but not frequently, e.g. one or two a year in the USA. Most commonly, these cases occur in persons with direct exposure to pigs. There are a few previous cases of one person transmitting swine flu to others.

8. What are the symptoms of swine flu?
The symptoms of swine flu in people are similar to the symptoms of regular influenza, including fever, lethargy, lack of appetite and coughing. Some people with swine flu also have reported runny nose, sore throat, nausea, vomiting and diarrhea.

9. Should I travel to Mexico / the USA?
The World Health Organization (WHO) is not presently advising against travel to Mexico or the USA. National governments may be offering different advice (check locally). Travellers to affected areas are advised to consult a doctor immediately if they show signs of flu-like symptoms.

10. More information:

• CDC
• WHO
• UK HPA
  • UK HPA pandemic influenza FAQ
  • UK national framework for responding to an influenza pandemic
• MicrobiologyBytes: Influenza

11. Are we all going to die?
Probably not. Every year many thousands of people around the world die as a result of influenza, a fact which goes largely unreported. The number of deaths increases in epidemic years. Pandemics (worldwide epidemics) occur unpredictably every 10-30 years. Millions of people die, billions survive.

Update: 10 more things you should know about H1N1 (swineflu)

Bluetongue is a highly infectious virus disease of ruminants. Cattle and goats are major hosts of the virus, but in these species infection is usually asymptomatic despite high virus levels, allowing the disease to circulate in the absence of any symptoms. Sheep and deer are usually the only species to exhibit symptoms of infection. Bluetongue infections are marked by a high fever, excessive salivation, swelling of the face and tongue and cyanosis of the lips and tongue (turning blue). Infected animals become lame and listless. Ulcers appear around the mouth, nose and eyes. Then the neck may start to swell, followed by the head. The animal becomes lame, starts bleeding internally and breathing becomes difficult. The incubation period for bluetongue is 5-20 days. The mortality rate is normally low, but infected animals lose condition and there is a high mortality rate of 70% or more in susceptible breeds of sheep (due to secondary bacterial infections). While infected animals can recover, productivity is reduced with milk yields in dairy herds dropping by about 40%.

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Bluetongue virus (BTV) is a Reovirus of the genus Orbivirus. The virus is transmitted by midges, in particular Culicoides imicola and a few other species. Of more than 1,400 species of midges known world-wide, only around 20 culicoid species are known to be involved in transmission of bluetongue virus. Bluetongue can also be transmitted directly from one animal to another through semen and transplacentally. Bluetongue occurs in Australia, the USA, Africa, the Middle East, Asia and Europe, generally between latitudes 35°S and 50°N. It occurs around the Mediterranean in summer, subsiding when temperatures drop in winter. In Europe the disease has been spreading north since October 1998, possibly as a result of climate change. In August 2006 bluetongue spread to the Netherlands, then Belgium, Germany, Holland, and Luxembourg. The first ever case of bluetongue in the UK was reported in Suffolk on 23rd September 2007. On 28th September 2007 Defra confirmed that bluetongue is now endemic in the UK.

Unlike foot and mouth disease, bluetongue cannot be controlled by culling of infected livestock alone. Since midges form a reservoir of infection in endemic areas, you would also need to kill all the midges to eradicate the disease. Another complication is there are at least 24 distinct serotypes of the virus (based on the lack of cross neutralisation). Vaccination against one serotype does not usually confer protection against any of the other serotypes. The antigenic diversity of Bluetongue virus is due to both antigenic drift (accumulation of point mutations) and antigenic shift (reassortment of individual gene segments). The virus which has affected northern Europe and the UK is known as BTV8.

Live attenuated BTV vaccines containing a weakened form of the live virus are cheap, easy to produce and can be administered in a single dose. They are effective in controlling clinical outbreaks of bluetongue. However, the disadvantages of attenuated BTV vaccines are:

• Risk of reassortment with virulent wild viruses which potentially could give rise to new virulent strains.
• Potential for reversion to virulence both in the vertebrate host and in vector insects.
• Attenuated BTV can cross the placenta and pregnant ruminants vaccinated with attenuated vaccines may suffer foetal loss.
• Existing vaccines are designed for sheep; there is little data on their safety and effectiveness in other species.

There have been attempts to develop inactivated (killed) whole virus vaccines for BTV for the past 25 years, but none have yet been produced commercially. Inactivated vaccines are they more expensive to produce than attenuated vaccines and also require at least two doses with an adjuvant to generate a protective immune response. Bluetongue virus is not usually contagious for humans, and meat and dairy products pose no hazard. However, there is some concern over the potential spread via blood from infected people.

Bluetongue: Latest News

Related:

• Will bluetongue come to the UK on the wind in 2007?
• Sheep virus ‘low risk to the UK’