Category Archives: History of Microbiology

TB or not TB – that is the question?

As usual my delving into family history has prompted a post … I’ve been researching my Great-great-Uncle who was killed in action at Somme, France whilst serving as a WW1 ANZAC and discovered that his father, my great-great-grandfather died from (and I shall quote from the Marlborough newspaper that it was printed in) … “that dread disease consumption“.

Now you may consider TB to be a third world, old-fashioned type of disease and to a degree you would be right however TB remains the second greatest killer globally (HIV/AIDS is number one) due to a single infectious agent.  In 2013, 9 million people fell ill with tuberculosis and 1.5 million died as a result – 480,000 of these cases were MDR-TB (multi drug resistant).  There is an upside to all this in that 37 million lives were saved due to effective diagnosis and treatment between 2000-2013 and the number falling ill to the disease each year is declining albeit slowly.  New Zealand statistics show 305 cases nationwide during 2014 and this number has been relatively stable over the past five years.

MDR-TB is defined as those strains that are resistant to at least Isoniazid and Rifampicin (the two most powerful and standard first line drugs for treatment of TB).   XDR-TB are strains that are extensively drug resistant and are defined as MDR-TB with additional resistance to any fluoroquinolone and at least one of the second line agents (Amikacin, Capreomycin or Kanamycin).  Of the 480,000 MDR-TB cases in 2013 about 9.0% of these were determined to be XDR-TB.  Within New Zealand the rate of resistance is much lower, on average only 1-2% of isolates each year showing this level of resistance.  In the past 10 years there have been 33 cases of MDR-TB in good ol’ NZ and all but two of these cases were born overseas where it has been assumed they contracted it – 29 of these 31 cases were born in an Asian country.  Only one case of XDR-TB has ever been identified in New Zealand, this was in 2010.  I think this is one time were our geographical isolation from a large part of the world is to our benefit.

Tuberculosis was a disease that the WHO considered dropping from their watchlist in the 1960’s/1970’s due to it’s decline however it made a huge resurgence in the 1990’s with the number of HIV/AIDS cases increasing and is certainly a disease which we cannot afford to ignore.

You can view a copy of the 2014 WHO global TB report here.

Nitpicking

I’ve been doing some reading lately, mainly on the subject of World War I and it naturally brings to mind topics for this website ….. this time “lice”.

Why are we not able to eradicate parasites such as lice?  Surely if the little blighters do not have a host to live off then they die therefore minus the hosts and we shouldn’t have issues of lice, yes?

I guess it is the age old problem of compliance … there is always a host somewhere who is not willing or able to get rid of them and therefore continues to spread them to those who spend many hours and much money to de-louse their children (mainly) from these wriggly little pests.  I am referring in general to head lice which seem to be a fact of life throughout most kids journey through primary school however with the very popular “selfie” causing a surge in cases in older age groups also.  It is the sort of nuisance that if everyone cared enough to treat and eradicate then we should be able to get rid of ……

The head louse ( Pediculus humanus capitis) is essentially a harmless pest.  It is a wingless insect which spends its entire life on the head of a host feeding off small amounts of blood.  They cannot fly or jump and do not transmit disease although they can be responsible for secondary infections of the skin due to scratching.  They are simply a nuisance and one that should be able to be eliminated from our society.

Body lice (Pediculus humanus corporis and sometimes Pediculus humanus humanus), common during the Great War, are far more dangerous due to their potential to transmit  diseases such as typhus and trench fever.  The two species are physically very similar, almost indistinguishable, but do not interbreed however they have been known to under laboratory conditions.  Again a parasitic pest that should be able to be eliminated with adequate hygiene practises.

If the world can eradicate smallpox (Variola virus – declared obsolete by the WHO in 1979) then why can we not do the same with our Pediculus friends?  Just as we needed the “buy in” of people to get vaccinated against smallpox we should be able to get their “buy in” to de-louse.

“Adding meaning to methicillin”

 

You will all be familiar with the acronym MRSA (Methicillin Resistant Staphylococcus aureus), but you probably won’t be so familar with the methicillin part, unless you are even older than me.

Methicillin was the first semi-synthetic beta-lactam and was manufactured by Beecham and released commercially in 1959. This antibiotic was a marked improvement on the original penicillins such as Penicillin G (benzylpenicillin). Scientists had discovered that by making the side chain of the beta-lactam ring bulkier, the “steric hindrance” produced made the antibiotic more stable to penicillinases. At that time at least 50% already of all Staph aureus isolates produced penicillinase and were thus resistant to straightforward penicillin.

However a major problem with methicillin is that it is poorly absorbed when given orally and it is broken down rapidly by acid in the stomach. In 1961, Beecham released newer penicillinase stable beta-lactams called oxacillin and cloxacillin (flucloxacillin was first used commercially in the early seventies). These newer antibiotics were much more stable when given orally.

And as with all antibiotics, it did not take long before resistance to methicillin in the human population became prevalent. The first Staphylococcus aureus isolate resistant to methicillin (MRSA) was described in 1961 in the UK.

Clinical use of methicillin tapered off during the 1980s and as far as I am aware the antibiotic is no longer available commercially, but the name Methicillin Reistant Staphylococcus aureus continues to this day.

Maybe we should change the name of MRSA to BRSA… The mechanism of resistance in MRSA (mecA gene encoding for altered PBP2a) confers resistance to not just methicillin, but all beta-lactams. For me, the acronym BRSA makes it clear what antibiotics can be excluded for starters in treatment of an MRSA infection.

Michael

p.s. The taxonomical establishment have since changed the name of methicillin to meticillin, for reasons which are best known to themselves….