Infection transmission

 The COVID-19 pandemic should have got us all thinking about infection transmission and control.  Yet, the virus continues to spread.

I remember the pretty much the first laboratory class we did in Microbiology 101 was a demonstration of how infection transfers within a community.  There were 24 students in the class.

First, everyone wiped their hands with a paper tissue, one of which had been contaminated with a bacterial culture.  This organism was Serratia marcescens, which produces a bright red pigment when grown under the right conditions.  A sequence grid was set up, so that everyone shook hands with one other class member and then plated their hand onto an agar plate.

The second round of hand shakes was then undertaken with different class members, without first washing our hands, and, again, hands were plated.  This sequence continued until, by the end, everyone had shaken hands with about 10 classmates and plated their hands.

The plates were incubated, and a couple of days later were examined for the presence of the bright red colonies.  Scoring the positives against the sequence grid, it was very obvious how the infection had spread throughout the class.  Not everyone became infected initially, but the infection spread exponentially and after six rounds, everyone in the class was positive.

How is this relevant to COVID-19 spread?  This virus is supposedly spread predominantly by droplet inhalation.  However, an individual may become infected by touching their face with infected hands or perhaps by rubbing their eyes.  The virus, like the Serratia, might be picked up on the hands from surfaces like door handles, wash basin surrounds, pens, or from shaking hands with a carrier etc.  "OK, I don't touch my face and eyes".  Are you sure?  I used to lecture to classes of up to 130 students and occasionally counted how many were touching their face at any one time.  (Yes, I know, I had put half of them to sleep and their heads were in their hands).  Up to 60% of the class touched their faces and noses and eyes.  A similar surreptitious survey found that up to 30% of students left the toilets without washing their hands!

The take-home message here is - "Wash and sanitise your hands regularly - many times a day; avoid hand shaking and kissing 😞 and if you are sick, STAY HOME.  In fact, if you don't have to mix with people, stay away from them."  Like in our first year experiment, there was no indication that any particular person was carrying the infection until two days later when the test results were available.

Update:  As of today, 10th July 2021, we have seen over 4 million people die of COVID-19 around the world and it is now obvious that the primary route of transmission is by inhalation of virus particles.  Mask wearing significantly reduces the spread of the virus by trapping droplets and by wearing a mask, you are protecting others.  In countries where people still gather together in crowds, the virus is spreading very fast and the delta variant, which is highly infectious, is ripping through the population.

If you are reading this update and you have the option, please GET VACCINATED, both for your own safety and the protection of your friends and family.

Safe Food in Lockdown

Are you tired of reading and hearing about COVID-19 yet?  Are you totally confined to your home, or are you an essential service worker?  How have things changed for you?

My on-line news service provides the ten top items each day as links.  For the last two weeks, nine out of the ten have been about COVID-19 and mostly they provide depressing reading.  I'm not going to rehash all that.

New Zealand, where I live, has closed its borders. 

The majority of shops are closed, so our food shopping is mostly confined to visits to the supermarket, which may involve long queues and limited numbers of people in the building at any time, so the on-line ordering and collection option is popular. The 2-metre separation rule is now being followed by most people.

How does this affect our eating habits?  Well, restaurants and fast food joints are closed, so we are all preparing many more meals at home from what we have on hand.  This may involve substitution of ingredients, or complete change of menu at short notice.  Not everyone is used to cooking meals at home and there may be a few disasters! 

Do we need to worry about contracting the virus from our food?  The best information I have is that this is a respiratory infection and you can't pick it up from food.  Since it is a virus, it can't replicate in stored food, so the only concern is with contamination of the packaging.  Survival time on surfaces seems to vary, but studies by CDC, researchers at various universities and FDA indicate that the survival time varies from a few hours to about three days, but it is important to remember that the AMOUNT of virus remaining may be as low as 0.01% of the original contamination.  It is unlikely that you can contract the virus from food packaging, but it's a good idea to wipe the packaging down with a 1:48 dilution of household 6% bleach, (5mL 6% bleach into 240mL water) or just leave the packages unopened for a few days.

So, do we need to change our cooking and eating habits?  Essentially, I think the answer is "No" but we do need to be very careful.  Nobody wants to waste food, so it's likely that leftovers will be stored for future use.  We don't want to burden our hospitals with food poisoning cases.  Here are a few tips:

Keep leftovers refrigerated and reheat to at least 75C - use a thermometer
Wash your hands thoroughly and frequently
Don't touch your face
Ensure that food is cooked properly (as you would normally) 
Be very wary of cross contamination of raw and cooked food
Stay home; don't pop down to the corner store just to pick up a bottle of milk - plan your shopping.

Just a couple of final points:
The experts now think that the wearing of masks available to the general public is not going to protect you from infection.  Don't forget that the virus is tiny and if you get it in your eyes, it will run down your tear ducts into your nasal passages and can initiate an infection

I am now washing my hands more thoroughly and frequently than when I was working with green lipped mussels deliberately infected with high levels of Salmonella!

Do antibacterial soaps and wipes have any effect on antibiotic resistance? Should we use them in the home?

Over the Christmas holiday, our kitchen has fed more people than normal and cleaning has therefore increased.  I have been giving a lot of thought to the possible benefits and risks of using antimicrobial cleaners and soaps.  When you get into this subject, you find it is actually quite complex.

I have written about something similar before, but there is now a lot of published work that suggests that in most cases, there is no benefit to using antibacterial soaps in the home - there is no statistically significant reduction in infectious disease if antibacterial preparations are used in preference to soap and water*.  Nevertheless, in the US alone, nearly $1 billion per year is spent on antibacterial soaps**.

Of course, many infectious diseases are caused by viruses; they are probably not affected by antibacterial compounds, which have a definite target in the bacterial cell.  Thus, an antibacterial soap or wipe will be no better at preventing transmission of cold viruses than a thorough cleaning with soap or detergent and water.

I have recently been asked to review a couple of scientific papers in which evidence is presented that suggests cleaning agents commonly used in the food industry may induce antibiotic resistance in bacteria.  Antibiotic resistance results when bacteria develop enzymes capable of breaking down the active component of the antibiotic.  One of the first instances of antibiotic resistance occurred very soon after the introduction of penicillin.  Bacteria developed the ability to break the beta-lactam ring of penicillin with an enzyme called beta-lactamase.  (Antibiotic resistance genes can often be transferred from one bacterium to another, so in time, many bacterial strains become resistant.)

We already know that many of our antibiotics are no longer effective because of resistance.  Overuse of antibiotics is blamed.  It is ironic that our cleaning agents may also be causing resistance.

But there is another potential driver for antibiotic resistance: sub-lethal exposure of bacteria to certain herbicides have been shown to change antibiotic susceptibility of Escherichia coli and Salmonella enterica serovar Typhimurium***.  This is not a straightforward relationship, but it is clear that there is the potential to select for antibiotic resistance in these bacteria, which, if transferred to humans by contact with animals and food, can potentially reduce the effectiveness of antibiotic therapy.

Well, that's fairly heavy for the first post of 2016, but it should cause us to think when purchasing home cleaning agents and soaps, or chemicals for use in agriculture and domestic gardens.




* Effect of Antibacterial Home Cleaning and Handwashing Products on Infectious Disease Symptoms.  Larson, Elaine L;Lin, Susan X;Gomez-Pichardo, Cabilia;Della-Latta, Phyllis.  Annals of Internal Medicine; Mar 2, 2004; 140, 5

** https://www.nrdc.org/health/files/antimicrobials.pdf

*** Kurenbach B, Marjoshi D, Amábile-Cuevas CF, Ferguson GC, Godsoe W, Gibson P, Heinemann JA. 2015. Sublethal exposure to commercial formulations of the herbicides dicamba, 2,4-dichlorophenoxyacetic acid, and glyphosate cause changes in antibiotic susceptibility in Escherichia coli and Salmonella enterica serovar Typhimurium.  
mBio 6(2):e00009-15. doi:10.1128/mBio.00009-15.

Vomiting and Diarrhoea doesn't necessarily mean food poisoning.

If someone reported that they had vomiting and diarrhoea, I would normally suggest that they had contracted food poisoning.  Further questions about recent meals, travel history, etc. would help to clarify the situation.

However, with the current Ebola virus outbreak in West Africa - Sierra Leone, Guinea and Nigeria - and two Americans apparently infected, together with a reported potential case in Sydney, the possibility of a world wide epidemic is not far fetched.  


Ebola viral disease is not new - it first appeared in 1972, just after I qualified as a microbiologist, in the Sudan and Democratic Republic of Congo.  There was then and still is no licenced vaccine and the fatality rate can be as high as 90%.  

Ebola is not transmitted by food.  The reservoir appears to be wild animals and there are documented cases of transmission of the virus to humans through handling or contact with bodily fluids of infected chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead or in the rainforest (WHO, 2014).  Transmission is then human to human, again by contact with bodily fluids through broken skin or mucous membranes.  Contact with environments contaminated with fluids from infected individuals can also result in transmission.

According to staff at the Mayo Clinic, signs and symptoms typically begin abruptly within five to 10 days of infection with Ebola or Marburg virus. Early signs and symptoms include:

• Fever

• Severe headache

• Joint and muscle aches

• Chills

• Weakness

Of course, some other diseases including influenza can produce similar symptoms. However, in the case of Ebola viral disease, symptoms become increasingly severe and may include:

• Nausea and vomiting

• Diarrhea (may be bloody)

• Red eyes

• Raised rash

• Chest pain and cough

• Stomach pain

• Severe weight loss

• Bleeding, usually from the eyes, and bruising (people near death may bleed from other orifices, such as ears, nose and rectum)

• Internal bleeding

There is no need to panic if you or family members have vomiting and diarrhoea, but the application of sensible precautions can help to limit the spread of the virus or any other causative agent.  Air travel is a very rapid way for infections to spread around the world.  If you have been in Central or West Africa within the last few days and start to show the early symptoms listed above, you should immediately contact a doctor and, to be fair to your fellow man, avoid air travel.  If you have been on an aircraft where someone had vomiting and diarrhoea, it might also be a good idea to consult a doctor, even thought the cause is most likely food poisoning.

As with all cases of vomiting and diarrhoea, take great care with personal hygiene and ensure that those people looking after you do the same.  The chances are that you don't have Ebola, but this outbreak looks to be the most widespread so far. 

WHO (2014)  Fact sheet N°103. Updated April 2014.Retrieved from:  http://www.who.int/mediacentre/factsheets/fs103/en/

Safe Food in Troubled Times

On 4th September, 2010, Christchurch was violently shaken by a Magnitude 7.1 earthquake.  On 22nd February 2011, an M 6.1 shock destroyed much of the city centre and since that time, there have been about 3400 shocks of greater than M 3.

After the February earthquake, I expected to read of food and water related diseases spreading through the population - the water supplies were seriously damaged and sewer pipes were destroyed, while liquefaction of the ground allowed mixing of ground water and sewage to occur.  Contamination of water supplies by faecal bacteria and viruses was therefore a serious consideration.  People handling food for themselves and others would have to take great care with personal hygiene and cleaning of food preparation areas.

Amazingly, there were no major disease outbreaks.

New Zealand sits on the Pacific Ring of Fire and is sometimes called The Shaky Isles.  We are taught to look after ourselves during a shake and to make preparations to look after ourselves in the aftermath.  In my rumpus room out back, I have a cache of canned food and bottled water.  But how many of us expected the Christchurch earthquakes to go on for so long?  My cache would last for only a couple of days.  Some people in badly damaged areas had to cook in their gardens on barbeques and open fires for many days.

This set me thinking about security of food supplies after such disasters.  I guess that natural disasters are one thing; what must it be like when those waging civil war deliberately set out to destroy infrastructure?

We can expect that help might take a few days to arrive.  Local emergency services will be overwhelmed by the number of people requiring assistance and their own degraded response capabilities - roads will be damaged and may be impassable for emergency vehicles.  Stores and warehouses may be destroyed, power supplies will be interrupted and food may therefore be scarce, spoiled and possibly contaminated.

The first few days are therefore critical for the population to survive and begin rebuilding their lives.  A secure and safe supply of food and water is essential.  How does the average family prepare for their own and their neighbours' welfare?  Dried and canned foods provide a safe and stable basis for the emergency supply.

There are many websites that will help you plan.  Civil Defence in New Zealand provides lots of valuable information, such as lists of things you need in a survival kit; commercial organisations offer ready-made kits and meals that can be prepared with minimal resources. 

I don't endorse the following sites or products, but you may find them useful.

http://www.pcc.govt.nz/A-Z-Services/Emergency-Management/It-s-Easy---Get-prepared/Emergency-Food-Stores

http://www.prepare.co.nz/default.asp?c=11655

http://www.efoodsdirect.com/

http://whatscookingamerica.net/LeaSchneider/EmergencyFoodPantry.htm

http://www.bt.cdc.gov/preparedness/kit/food/

A quick search on one of the major search engines will provide you with many more links to valuable information.



If you want more information on the Christchurch earthquakes, see the following:

http://www.christchurchquakemap.co.nz/

http://www.geonet.org.nz/var/storage/images/media/images/earthquake/aftershock_decay/58870-7-eng-GB/aftershock_decay.png

Giving bacteria a cold

I hope that title got your attention. I could equally have used "Fight fire with fire" or "Biological warfare".

Food Standards Australia New Zealand is calling for submissions on an application to use viruses to aid in the control of Listeria monocytogenes.  L. monocytogenes is a bacterium found in the environment that can infect food and may cause listeriosis.  The majority of the population is unaffected by Listeria, but it is a hazard for pregnant women, young children and the elderly, in addition to those who are immunocompromised.  Note that you don't have to have had an organ transplant to be immunocompromised - you might just have another infection stressing your immune system.

You might think that deliberately putting viruses into foods is crazy.  However, these viruses are special.  They exclusively target bacteria and are called bacteriophages.  Bacteriophages (or "phages") are extremely common; they occur at levels up to 9×10⁸ per mL in bacterial mats at the surface of the sea.  They were first identified in 1915 by Frederick Twort in England and, independently, in 1917 by Felix d'Herelle in France.

Bacteriophages are deceptively simple - essentially a piece of nucleic acid contained within a protein coat called a capsid.  They can't reproduce independently and have to have a means of infecting a living cell.  Perhaps the most famous phage is the T4 phage that infects Escherichia coli and always reminds me of the lunar lander.  (I sometimes wonder how something like this could have evolved by chance).  See image from Wikipedia below.  

 When a phage infects a bacterial cell, it injects its DNA into the cell.  The viral nucleic acid then takes over the bacterial synthetic machinery and makes copies of itself, and synthesises new phage coat and other components.  The components are then assembled into new phage particles, whereupon the bacterial cell is lysed and releases the phage.  Burst sizes may be around 100 viruses per bacterial cell.  Since these are all infective, the infection of the population proceeds rapidly, resulting in the death of the majority of the bacterial cells.  Phages cause the cheese-making industry a lot of trouble, because they kill the starter bacteria.

The application currently under consideration is for the use of a mixed bacteriophage preparation, sold commercially as LISTEX™ P100, as a processing aid.  This preparation was the first phage product to be classified as Generally Recognized as Safe (GRAS) by the FDA  and USDA.

A number of scientific papers have been published on the efficacy of the P100 preparation, showing that the phage significantly reduces the population of L. monocytogenes on foods, such as salmon fillets or surface-ripened cheeses*.

The use of bacteriophage to control pathogens, such as Listeria and Salmonella, can reduce the risk of food poisoning, though it is unlikly that it can be a total solution, as the pathogen population may not be totally destroyed.  However, when used in an integrated food safety programme, the processing aid can be a valuable tool, reducing the reliance on chemicals to inhibit the bacteria.

*  See:  doi:10.1016/j.yrtph.2005.08.005

Electron micrograph of T4 phage adsorbed to a bacterial cell.

Image by Elizabeth Kutter, Bacteriophage Ecology Group

http://www.mansfield.ohio-state.edu/~sabedon/beg_phage_images.htm

Odd Spot:  When I was researching this post, I searched on "Listeria virus".  I got many hits, predominantly in popular press and websites, where the Listeria bacteria were described as "viruses".  In modern microbiology terms, this is totally wrong.  However, "virus" is derived from the Latin word for poison and this apparently appeared in the English lexicon in 1392. "Virus" was also used in 1728 to describe an "agent that causes infectious diseases".  I'm sure that most of those press writers didn't know this, but, strictly, they were correct.

Sarah Carter - confusion reigns

On 12th March, 2011, I wrote about the tragic death in Chiang Mai of Sarah Carter.

Originally, her death was blamed on consumption of toxic seaweed.  At the time, I suggested that this was a highly suspect conclusion, based on the symptoms and the circumstances.

A short while later, it was claimed that Sarah and her two friends had been infected by an ECHO virus.  The symptoms matched.

However, more information came to light - a Thai tourist guide had died in the next room in the same hotel and a week earlier, two other tourists had died in a room one floor below. 

The New Zealand TV3 channel discovered that a total of seven tourists had died in Chiang Mai in similar circumstances.  Sara Hill, an investigative reporter for TV3, went to Chiang Mai and made a programme screened here a couple of weeks ago.

In an interview with Sarah Carter's friend, Sara Hill discovered that none of the three girls had eaten seaweed and had eaten two different meals.  They all developed sore stomachs and vomiting and were hospitalised.  According to a Thai cardiologist, Sara Carter suffered very low blood pressure, dehydration and low blood flow to the kidneys, with ultimate kidney failure.

The reporter managed to obtain swab samples from the room occupied by Sarah and returned them to New Zealand for testing.  Traces of chlorpyrifos, an organo-phosphorus insecticide used in corn and cotton farming, were found in the swabs.  Dow Chemical Company voluntarily withdrew the registration of chlorpyriphos for domestic use in 2001.  Mr. Ron McDowell, a UN scientist, hypothesised that Sarah had been exposed to chlorpyrifos as a result of over-zealous spraying of the hotel room to control bed bugs by a pest control operator.  McDowell claimed that the symptoms and pathology all fitted with chlorpyrifos poisoning.

However, the swabs were taken three months after the room was occupied by Sarah, so spraying could have occurred at any time during those three months. The report form was shown in the programme.  The level in Sarah's room was given as <0.1 microgram/sample, which probably means "below the limit of detection".  A sample from an air conditioner was 0.24 micrograms/sample, but the film of the sample being taken suggested that the area swabbed was uncontrolled.

The half life of chlorpyrifos in the human body is about one day, so, although it is absorbed quickly, it also disappears from the body quickly.  Thus tests at the hospital may not have shown its presence in Sarah's body.

I'm not convinced that we are much further forward.  The Thai authorities were not being particularly cooperative with the TV3 investigation and recently refuted the chlorpyrifos theory.  Three toxicologists in New Zealand have issued a statement criticising the programme and the conclusions drawn by the experts consulted by Sarah Hill.


It looks as though seaweed is off the hook and food poisoning seems a bit unlikely, as the three girls ate different meals, but suffered similar symptoms not commonly seen in microbial food poisoning.  Food contamination is not completely ruled out, as several meals could have been contaminated with a chemical.

I don't know if we will ever know the true story

Toxic seaweed was a red herring

The tragic death of beautiful Kiwi backpacker, Sarah Carter, in Thailand last month was initially blamed on a meal containing toxic seaweed.  Sarah and two other women suffered vomiting and heart complications while they were staying in Chiang Mai.  Privately, I thought that this explanation was highly unlikely, partly because of the symptoms and partly because it appeared that only these three were poisoned.

It now seems that Sarah had been infected with an ECHO virus.  These Enteric Cytopathic Human Orphan viruses are found in the gastrointestinal tract and primarily cause disease in children.  (Their name originated in the 1950s, when cell culturing allowed the viruses to be identified, but no disease was associated with them). 

ECHO viruses are highly contagious and exposure to them can result in an infection of the lower intestine, which then spreads to other organs.  Death is usually the result of overwhelming liver failure or myocarditis (inflamation of the heart muscle).

Because of their association with the gastrointestinal tract, ECHO viruses are usually transmitted by unhygienic conditions and person-to-person transmission via the faecal-oral route.  Respiration of infected droplets and contact with fomites (contaminated objects) may also be important in transmission.  I believe that it is significant that three other people died of heart problems in the same hotel in the space of two weeks, though a doctor from the Thailand Department of Disease Control said that the elderly British couple who died both had blocked arteries.

I guess that the messages we can take from this tragedy is that foreign travel is wonderfully mind-broadening, but that visiting areas where environmental and food hygiene are poor can be hazardous to health.  We should be careful, however, before thinking that Asia is the only
place we can contract ECHO viruses - poor hygiene can be found in any country.