Malaria deaths: twice what we thought

In the book we suggest that deaths from malaria, mainly from Plasmodium falciparum infection, could be far greater than those recorded by the World Health Organisation (WHO), due to the recording methods used and the large errors inherent in estimating deaths from sometimes limited data. In the lecture in January I suggested that actual deaths from malaria may well be twice that recorded by WHO.  Now, in a paper published today in The Lancet (details below) a team from the Institute for Health Metrics and Evaluation, University of Washington, Seattle, USA present an analysis of malaria mortality over the last 30 years, and indeed suggest that the world-wide death toll from malaria in 2010 was 1.24 million, around twice the figure of 655,000 estimated by the WHO in their World Malaria Report 2011.

Of course, this figure is also only an estimate, and the methods used are likely to come under intense scrutiny in the coming months, but the data in this paper does lead to a number of important conclusions.

  1.  Global malaria deaths increased from 995,000 in 1980 to a peak of 1,817,000 in 2004, and have fallen since to 1.24 million in 2010.  This almost doubling of the death rate over 24 years gives stark confirmation of the scale of the collapse in efforts to eradicate the disease and the increasing resistance of the plasmodium to drugs and the vector mosquitoes to pesticides.  More positively, it also demonstrates the great progress that has been made in the last few years, with the widespread use of bed nets, artemisinin-based treatments etc.  But it should be realised here that these were both available in 1980, yet it took over 20 years for them to be fully utilised.
  2. Malaria deaths in those over 5 years old in 2010 was much higher than previously thought: 524,000 deaths compared to 91,000 estimated by WHO.  Current trials of vaccines are aimed at the under-fives, and bed nets are also being targeted at this age group. Greater consideration must now be given to older members of at-risk populations, who outside of sub-Saharan Africa make up over two-thirds of the deaths from malaria, and make up approximately 40% of deaths even within this region.  This emphasises even more the economic burden of malaria in afflicted countries.
  3. Malaria accounts for many more child deaths in subSaharan Africa than previously thought: estimated at 24% of total child deaths compared to 16% previously calculated in 2008.

Murray, CJL, Rosenfeld, LC, Lim, SS, et al. (2012)  Global malaria mortality between 1980 and 2010: a systematic analysis.  The Lancet 379, 413-431.  This paper is available electronically through our library for those who are registered, and for students registered on Exploiters and Exploited I have placed a link to it on Blackboard.

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The Kraken ate my homework

The Kraken is or was a gigantic sea monster said to have dwelt in the North Atlantic, off the coast of Iceland and Norway.  Although sea-dragons and worms have been reported since the ancient world, the term Kraken was not used until the mid-18th century, when Bishop Pontoppidan used it to refer to a sea monster, a species that Linnaeus briefly recognised and gave a Latin name to. In the lectures and book we discuss the rise of this mythology used to explain mysterious marine occurrences at a time when much of the marine world was unknown and often downright terrifying.  During the 18th and 19th centuries many reports of Kraken (in modern German the Kraken is both singular and plural) were published, often with excellent and fanciful illustrations. It was not until the 1870s when a number of the hitherto unknown giant squids (Architeuthis dux) were washed ashore near Newfoundland and could be examined that a possible explanation of the Kraken was forthcoming.  That did not stop popular authors, screenwriters etc. invoking the Kraken wherever possible, but at least halted the use of the expression in the scientific literature.  Or did it?

Fast forward to this October, when Mark McMenamin (of Mount Holyoke College, Massachusetts USA) presented a paper at the Geological Society of America Annual Meeting in Minneapolis.  In this (abstract available here) he hypothesised an explanation for an unusual assemblage of ichthyosaur bones found in a Nevada State Park; bones from nine ichthyosaurs, predatory marine reptiles about 15 m long, deposited about 228 million years ago. This assemblage has occasioned much interest since it was discovered in 1928 and many questions remain unanswered, including why are so many dead ichthyosaurs found in one place?  McMenamin suggests that these bones are the remains of the lair of a gigantic predatory cephalopod, which he terms the Triassic Kraken, twice the size of the modern colossal squid, which caught and brought back the reptiles to its den to dismember and eat. 

Although octopods have lairs, squids, including the giant squid do not, but the kraken at least as imagined by Alfred, Lord Tennyson in The Kraken, does, living ‘Far, far beneath in the abysmal sea’ in ‘many a wondrous grot and secret cell’ where he is ‘battening upon huge seaworms in his sleep’.

If that was not sufficient, McMenamin then proposes that this Kraken was the world’s first artist, arranging the reptile vertebrae in a pattern that resembles the pattern of sucker discs on a cephalopod tentacle, and thus that this cephalopod ‘which could have been the most intelligent invertebrate ever’ created the earliest known self-portrait.  I think he has been reading far too much H.P. Lovecraft!

As you might expect, this story has caught the imagination of the media: a quick Google search of ‘McMenamin Kraken’ today came up with ‘about 121,000 results’, and the title of some of the articles says it all:

‘Kraken versus ichthyosaur: let the battle commence’

‘Artistic mega-octopus may topple ichthyosaur from top of Triassic’

‘Unleash the Kraken!’

‘Seeing a Cephalopod in ancient bones’

‘Giant sea monster discovered in desert’

‘Triassic Park – the last word in nothing’

‘Kraken or Krakpot?’

‘Giant prehistoric Kraken may have sculpted self-portrait using ichthyosaur bones’

‘Smokin’ Kraken’

‘The giant, prehistoric squid that ate common sense’

You can easily follow some of the reactions to this story on the web.

Part of the role of science is to occasionally think the unthinkable, and see if the resultant idea has any merit before one’s peers, and this is what McMenamin has done, along with providing a great story.  I think it would be fair to say, in this case, that few of his peers agree with McMenamin’s hypothesis.  And, for those of you taking the module, I am afraid I won’t be accepting (unless backed up by very good evidence) the excuse given in the title of this piece as a valid reason for you not handing in your end of term essay on time at the end of the week!

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Silkworm Update 4

Soon after my last update the first of the silkworms started to show signs of wanting to spin a cocoon.

Growm worms ready to pupate

  I had prepared an insect rearing cage for them, and placed the plastic boxes containing the larvae into the cage and added some ‘mountages’, in this case some twigs of cherry and apple.

The silkworm cage ready for mounting and pupation

  I hoped that the silkworms would like to climb these and spin their cocoons away from the leaves and detritus in the containers.

A silkworm starting to spin its 'bave'. This is a loose weaving of silk fibres used to make a rough cage in which the cocoon is formed. It does not form part of the cocoon.

Well, it sort of worked.  Some larvae did mount the sticks, but most then climbed up the inside of the cage and pupated in the corners of the cage, at least they were out of the containers.  Many, however, did not bother to move and pupated close to the ground, in their containers.  As the density of larvae was not high, they were not too crowded and all the larvae that survived (again many died during pupation) managed to find somewhere to pupate.  There is obviously a lot of experience necessary to produce good mountages for these larvae.


Silkworms starting to form their cocoon inside the bave, morning.


By afternoon the worms were well on the way to producing their cocoons.


By the following morning the cocoons were fully formed


Interestingly, all but one of the cocoons was yellow.  I’m not sure why this was, was this due to the variety of silkworms, or the food that they were fed upon?

After a week, many of the silkworms had pupated, all around the cage.

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Ammonite feeding

A painting of a reconstruction of an ammonite. Apart from the shape of the shell, the rest is entirely conjecture! Illustr. Paul Hatcher

Although ammonites were the most species-rich group of cephalopods and are among the most abundant fossil animals to be found, in many ways they remain an enigma.  For example, what did they feed upon and why did they all die out at the end of the Cretaceous, about 65 million years ago?

The major problem in trying to answer the first question is that very few non-‘shell’ remains of ammonites exist, and although it is tempting to make comparisons with the still-extant (just) nautiloids, this is dangerous, as we do not know how similar these two groups really are.  Jaws have been found in 43 ammonite genera, but radulae in only 9 genera.  One view, which we put forward in the book, is that ammonites were largely bottom-feeders, pushing their shovel-like lower jaws along the sea bed and thus sweeping up detritus and small creatures.

Recently Isabelle Kruta and colleagues in France and USA (Kruta et al. 2011) have examined the upper and lower jaw and radula (together termed the buccal mass) from the ammonite Baculites, using, for the first time, synchrotron x-ray microtomography.  This has enabled them to produce a three-dimensional reconstruction of the jaws and radula apparatus.  They conclude that the buccal mass of these ammonites, including small delicate teeth on the radula, is most consistent with these creatures feeding by capturing and eating small organisms in the water column – plankton.  This view is strengthened by the finding of possible planktonic prey in the buccal mass of this specimen.

Can this new information be used to answer the second question above?  Kruta and colleagues think so.  They postulate that plankton feeding may have contributed to the extinction of the ammonites, as several groups of plankton also suffered a severe decline at the end of the Cretaceous, and they compare this with the nautiloids which fed on other food sources and did not become extinct.  This may be taking the results from the study of one fossil a bit far: ammonites, at least in shell shape and size, were a very diverse group, and it is certainly possible that they had a range of feeding habits, and yet they all went extinct.  However, in a useful commentary to this report, Kazushige Tanabe (Tanable 2011) has developed this idea, suggesting that ammonites laid a large number of small eggs, producing small larvae that would be plankton feeders, and thus the late Cretaceous decline in plankton abundance would have affected both the adult plankton feeders, and the possibly greater numbers of larval plankton feeders.  We now need an examination of further ammonite fossils to add support, or otherwise, to this argument.

Kruta, I, Landman, N, Rouget, I, Cecca, F, Tafforeau, P (2011)  The role of ammonites in the Mesozoic marine food web revealed by jaw preservation.  Science 331, 70-72

Tanabe, K (2011)  The feeding habits of ammonites.  Science 331, 37-38

Links to these papers will be available on Blackboard for students registered on the module.

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Insight into eel decline

I talked in the lecture on ‘Sargassum and the Sargasso Sea’ about the mysterious migration of the European eel (Anguilla anguilla): its putative spawning in the Sargasso Sea and then the return of the young eels (Leptocephali) to European rivers. Over the past few decades the population of the European eel has entered a steep decline, and although this is associated with over-fishing, diseases and changes to natural watercourses, the reasons are not fully understood. The problem has become so acute that the European eel is now classified as a critically endangered species.

The worrying decline in eels numbers is being investigated by Danish scientists, who captured 50 silver eels on their journey back from a river in Denmark to the sea, attached an acoustic transmitter to each, and then released them. The migration of the eels was monitored and the mortality rates at different parts of the river and fjord were estimated. Most of the eels survived the river part of the journey, but didn’t make it out of the fjord, suggesting that fishing is an important contributor to their demise. Read all about it here  and the primary paper is here .

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Silkworm update 3


Fifth instar silkworms having just finished all their food, again

I think I was a little premature last week in saying that most of the larvae were entering their fifth and final instar, as larvae have been moulting all this week, although I think now they are all in the fifth instar.   Some larvae are now 10-12 cm long and have bulked out, being 1 cm in diameter.  They certainly eat even the low quality food I have now for them (mainly yellow and senescing leaves) with relish, not stopping until the leaf is consumed.  I can understand why silkworm rearers say that the large larvae need feeding six times a day – there is only so much food you can give them at once, and they soon finish it.  At Reading, the larvae are fed three times a day during the week, and twice at the weekend.  In between they sit patiently waiting for more food to be provided.

Close-up of a fifth instar silkworm larva feeding. How many of the silkworm structures visible can you name?

Having larvae at different stages makes management of them difficult, and is certainly something that should be avoided when rearing silkworms commercially.  In our case it was probably not helped by having some of the larvae feeding slowly on artificial diet before being transferred to mulberry leaves.

Another fifth instar silkworm larva feeding

We have had continued, but luckily low levels of, mortality through the week, and this seems to strike particularly during the moulting process. This could be for a number of reasons, poor food, getting trampled by other larvae, or damaged during the daily cleaning of the rearing containers.  When I have noticed that a larva is about to moult I have tried to remove it to a separate container, so it can be left in peace and this usually has resulted in the caterpillar moulting successfully.

The photos below show part of the moulting process for one caterpillar, which seemed to be stuck with half the old skin still covering it. 

Silkworm larva with remains of old skin still attached to it. The little 'mask' that can be seen at the top right is the moulted head capsule from the larva - these tend to be moulted in one piece

I watched this larva thrashing around for 15 to 20 minutes and I thought it would not make it, but in the end it managed to extract itself form the skin, and was OK afterwards.  It is really apparent that moulting for these large caterpillars can be rather difficult.

The larva has now finally managed to finish its moult into the fifth instar

I hope that they will stop feeding soon, as there are virtually no even slightly green leaves left on the mulberry now, and that in my next update I can report on their pupation and cocoon formation.

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Silkworm update 2

It is almost two weeks since the silkworms arrived at Reading as first or early second instar larvae. 

Silkworms on Monday 31st October feeding on mulberry. Most have just entered their fifth and final instar.

The larvae feeding on mulberry leaves are now entering the fifth and final instar, and some are over 5 cm long and about 7mm in diameter.  I’m trying to rear them now at about 23C, which is a bit difficult as the rearing room, with assorted fridges and freezers, is not well ventilated and tends to build up heat. Still, I can keep the door open.

Some fifth instar silkworms on 31 October.

In the practical last week some people asked me what the moulted skin looks like, and I have a couple of photos below which shows this.

This silkworm has just moulted to the fifth instar, its moulted skin can be seen above it.


Two skins from silkworm larvae that have just moulted into the fifth instar. You can see the outline of their prolegs and body segmentation. The large black lump to the left of the skin on the left is the remains of the gut contents: the larvae moult their gut lining and their gut has to be completely empty before moulting.


 Unfortunately, the larvae feeding on artificial diet fared less well last week. Although I was careful to move them onto new food and sterilise the containers, many died.  I moved some more on to mulberry leaves, and they seem to be growing now, but although some of the remainder on artificial diet were growing and had entered the fourth instar, most were not and seemed to die during moulting.

Silkworms feeding on artificial diet on 31 October. These are the same age as those above, but are much smaller. A dead one can be seen top left.

  Thus, yesterday I decided to kill these larvae and preserve them while I still could, so that there are at least some demonstration silkworm larvae available in the coming years, if we cannot get live silkworms.

It will now be a race for the silkworms to complete growth before the mulberry leaves become unsuitable: yesterday there were not many leaves that were still green, and I picked most of them.  Also, I will have to prepare the mountages for them to spin their cocoons.

Close-up of a fifth instar larva feeding on mulberry 31 October.

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Medicinal honey

The medicinal properties of honey have been known for many thousands of years, the oldest records of medicinal use being from a Sumerian clay tablet of 2000 BC.  Indeed, in cultures where other sweeteners were available the main use of honey was in medicine.  For example, there are over 500 treatments listed in ancient Egyptian records in which honey is an important ingredient, it being used in wound dressings, for gut problems and even to cure tooth decay.  It was also used as a preservative in mummification: Alexander the Great (356-323BC) is said to have requested to be covered in honey after his death, to stop putrefaction before mummification, and small corpses have been found in Egyptian tombs preserved in large jars of honey.

Although honey continued to be used medicinally, especially in wound dressings for burns, with the rise of modern medical practices the use of honey became sidelined and it became considered an unsubstantiated folk remedy.  However, recent research has validated many of the originally described benefits of honey.  First, in the 1960s, the enzyme glucose oxidase was discovered in honey.  This is secreted by the bees’ hypopharyngeal gland and catalyses the oxidation of glucose in water, liberating hydrogen peroxide, a mild antiseptic.  Honey, being acidic and a very concentrated sugar solution, is already an inhospitable place for many microbes to grow, and glucose oxidase will further enhance the keeping properties of honey, important in the hive.

More recently, we have come to realise how little we know about the constituents of honey as further compounds with an anti-microbial property have been found in honey in the last 10 years or so.  For example, Bee Defensin 1 (BD1) is also secreted by the honey bees’ hypopharyngeal gland into some honeys; this is a peptide which has anti-microbial properties.  Furthermore, the antimicrobial compound methylglyoxal (MGO) can also be present in honey.

With increasing marketing and use of honey for medicinal purposes it becomes important to try and quantify and standardise their anti-microbial properties, as it is clear that these vary greatly, sometimes even within the same type of honey from the same area.  To this end, Kwakman et al (2010) have investigated the medicinal properties of two widely-available medicinal honeys, Revamil and manuka honey.  Revamil is made from honey produced in controlled conditions in The Netherlands from selected pesticide-free hives, and the honey is gamma-irradiated to ensure that it is sterile.  The honey is made into a soft hydrophilic gel which, their website claims, has beneficial effects in the treatment of burns, stimulating granulation, enabling wound closure, reducing swelling and pain and reducing scar tissue.  Manuka honey is produced by bees foraging on the manuka bush, Leptospermum scoparium, indigenous only in New Zealand and SE Australia.  Manuka honey is very variable in its antimicrobial activity, but some has been found to contain very high concentrations of MGO (this is formed from the high concentrations of dihydroxyacetone found in the nectar from manuka bushes, although we don’t know how or why).  The anti-microbial activity of manuka honey is tested, and only honeys with a high level of activity are able to be sold as active manuka honey, with anti-microbial properties.

Kwakman et al (2010) tested these two honey products against a range of medically-important bacteria, and measured the concentration of anti-microbial compounds.  They found that the two products had quite different properties. Revamil honey contained high concentrations of hydrogen peroxide and BD1 and killed Bacillus subtilis, Escherichia coli and Pseudomonas aeriginosa within 2 hours, and killed methicillinin resistant Staphylococcus aureus (MRSA) within 24 hours.  Manuka honey, on the other hand did not contain hydrogen peroxide or BD1 but did have 44-fold higher concentrations of MGO than Revamil. While it was not so effective as Revamil against some of the bacteria after 2 hours, it was more potent after 24 hours and retained its activity at greater dilutions than Revamil.

There are still unknown anti-microbial compounds in honey:  Kwakman et al (2010) neutralised the MGO activity of the manuka honey and found that it still had a greater anti-microbial activity than an equivalent sugar solution.  As manuka honey hoes not have detectable amounts of BD1, this suggests that it has some other anti-microbial agents.

p.s. those who wish for more information on medicinal honeys might like to check out this link, which I found after writing the above.

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Silkworm update

The silkworms are growing well and some have now entered the third instar.

A third-instar silkworm, 24 October

It is now clear that the ones feeding on mulberry leaves are growing faster; many of these are now in the third instar, whereas few of those feeding on artificial diet are. The largest larvae are now almost 20 mm long, and will soon really start to feed and put on weight.

Silkworms feeding on mulberry, 24 October


It is interesting to watch the behaviour of the larvae on the two foodstuffs.  Those feeding on mulberry leaves are quite lively, wandering around over the leaves and each other and rearing up when the lid of the container is removed.  By contrast, those on the artificial diet are quite still with their heads down, feeding away. 

A group of silkworms feeding on artificial diet, 24 October

Now, to grow fast and produce large caterpillars with lots of silk, we don’t want very mobile caterpillars, wasting their energy and time on silly things such as moving; they should just be feeding – yet these are the ones growing fastest.

I was a bit concerned that although the temperature at 24-26C is OK, the humidity might be a little low in the rearing room.  Low humidity can impede moulting, with the larva dying in the process.  Thus, I have put some trays of water in the room, and the worms seem to be managing to moult to the third instar.

The caterpillars feeding on mulberry are quite well behaved, they soon move onto new food added on top of the old, and then the old food can be removed and the rearing container cleaned.  In contrast the artificial diet presents some problems.  The larvae seem reluctant to leave it for days, even when it has dried out and is covered with webbing, and I don’t want to move any more than absolutely necessary by hand, in case I damage the larvae.  I have tried adding new food on strips of margarine tub (food-grade plastic and thus can be sterilised), which works quite well, and can then be moved with the larvae to a clean container.  I have also tried placing the new food on a wire mesh above the old.

Placing new artificial diet on wire mesh over the silkworms in the hope that they will move to the new food has so far proved unsuccessful

  Unfortunately, the larvae are too small to be able to move onto this, and so I had to help them.

You might also like to have a look at this posting on another University of Reading blog where I talk about the mulberry species that we are feeding to the silkworms.

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Silkworms at Reading

Every year we try and obtain some silkworms, Bombyx mori, for the insects practical in Exploiters and Exploited, but we usually cannot find any for sale, as they are usually reared in the spring.  This year we were luckier; I found a supplier with some in stock and they arrived on Wednesday, less than 90 minutes before the start of the first practical!  Interestingly, these silkworms are not sold for silk production but to be reared as live food for pet reptiles. 

Our silkworms on 20 October, feeding on artificial diet

The larvae arrived as first and early second instars (the instar is the stage in between moulting, in which the larvae feed and put on weight), only about 5mm long.  They were supplied with ‘silkworm chow’ an artificial diet based on mulberry leaf powder.  This is often used in rearing, and means that you can rear the silkworms when mulberry leaves are not available.

Close-up of the 2nd instar silkworms feeding on artifical diet, 20 October

However, at Reading we do have mulberry trees, having established a small plantation of black and white mulberry a couple of years ago, and the bushes are now a reasonable size.

Our mulberry plantation on campus

  Thus, I have decided to try and rear some silkworms on their proper food, mulberry leaves.  This is a tricky decision at this time of the year – mulberry is deciduous and it will not be long before the leaves senesce and fall from the tree (although they are pretty healthy at the moment), yet mulberry leaf is a much better food for rearing larvae to pupation, and thus for silk production.  The problem comes if the mulberry leaves run out, as larvae then can be reluctant to go back to silkworm chow

So, on Wednesday afternoon I placed a couple of young mulberry leaves in the rearing container, and within minutes the larvae detected these leaves and started to move towards them. 

Silkworms being reared on black and white mulberry

The leaves were soon covered in larvae, and I removed them to a separate box and gave them more mulberry leaves. These are the first silkworms we have tried to rear on our own mulberry leaves. By Thursday morning it was clear that they had accepted this food (a mixture of black and white mulberry leaves), and to my eye the ones feeding on mulberry already looked larger and somehow healthier, dare I say ‘happier’ –what do you think?

Silkworms feeding on black mulberry, 20 October

If you have read the chapter on silkworms, or attended the lecture you will realise that silkworms are rather difficult to rear, and can catch all manner of diseases. 

Close-up of silkworms feeding on mulberry, 20 October. These are 2nd instar larvae and are starting to look recognisably like silkworms, although they are still less than 10mm long. Some are too small to eat through a leaf, instead they scrape the surface cells

To try and stop this from happening I am making sure that I scrub and then disinfect all containers and equipment that I use in rearing, and I am trying to keep them at a hot enough temperature.  At the moment I am rearing them at 24oC, when they are older this temperature can be reduced a bit, but should still be above 20oC. If the temperature is too low they become very sluggish, fail to feed, and are much more likely to die.

I shall report on their progress here, and you can always pop into the Wednesday practical over the next two weeks to see how they are growing.

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