CABI Blogs: hand picked... and carefully sorted

Did the dinosaurs die of malaria?

The other week I heard about a recently published book ('What bugged the dinosaurs? Insects, Disease and Death in the Cretaceous', by George and Roberta Poinar) which argues that disease-transmitting insects played an important role in the extinction of the dinosaurs. I have ordered a copy of the book so it can be indexed in CAB Abstracts, and in the meantime I have investigated some blogs, book reviews and news items that discuss it, and looked to see what else I can find on the subject in CAB Abstracts.

Most people reading this will probably be aware of the well-known theories that the dinosaurs became extinct as a result of the worldwide effects of an asteroid impact or large-scale volcanic activity. The book apparently argues that this cannot be the whole explanation as they had already been in decline for some time before the final extinction. This is consistent with what I had read before, although this news item from Science Daily refers to research suggesting the opposite, and the National Geographic news item about the book quotes others who say that there was no such decline.

A search of CAB Abstracts for articles by one or both of the authors of the book (whose work helped inspire the book and film Jurassic Park) revealed numerous studies on fossil insects preserved in amber. One¹, published in 2004, describes the investigation of an early Cretaceous sandfly; its gut contained both reptilian blood cells and protozoan parasites similar to the modern genus Leishmania, which is transmitted between hosts by sandflies. A number of others describe the finding in biting insects of protozoa similar to modern insect-borne pathogens; and another², of fossilized dinosaur faeces rather than insects, reports the presence of protozoan and helminth (trematode and nematode) parasites.

The suggestion is that insect-borne diseases emerged in the late Cretaceous period and had a significant effect on populations that had not previously been exposed to them; according to this blog entry at Science Blog, the authors compare the situation to the arrival of avian malaria in Hawaii, which killed off many of the native bird species. It is also suggested that insect pollinators may have promoted the evolution of flowering plants (an idea supported by several articles cited in a review with the intriguing title 'Did dinosaurs invent flowers?'³, which answers that question in the negative), which may have been less suitable for dinosaurs to eat. A further suggestion is that intestinal parasites may have been spread by non-biting insects. All these factors would have made dinosaur populations more vulnerable to asteroid impact, climate change and other likely causes of extinction.

Not everyone is convinced by the idea; see for example this blog entry by Daniel Cressey on nature.com -- although the identification of the parasites does not depend on the DNA evidence criticized there -- as well as some of those mentioned above. From what I have seen so far, it seems to me that it is an interesting idea, but that it would be difficult to prove. It is not clear to me why insect-borne pathogens would have suddenly developed virulence in the hosts in which they evolved (as opposed to being introduced to a previously unexposed host population as in the Hawaiian example). Also, the examples of parasites in fossilized insects are from the early Cretaceous period, tens of millions of years before the dinosaurs became extinct, so I don't know what the evidence is that they became more important in the late Cretaceous. I hope that we will be able to obtain a copy of the book to shed some light on this.

1: Poinar, G., Jr. and Poinar, R.: Evidence of vector-borne disease of early Cretaceous reptiles. Vector-Borne and Zoonotic Diseases (2004) 4 (4), pp. 281-284. doi:10.1089/vbz.2004.4.281.

2: Poinar, G. Jr. and Boucot, A. J.: Evidence of intestinal parasites of dinosaurs. Parasitology (2006) 133 (2), pp. 245-249. doi:10.1017/S0031182006000138

3: Barrett, P. M. and Willis, K. J.: Did dinosaurs invent flowers? Dinosaur-angiosperm coevolution revisited. Biological Reviews (2001) 76 (3), pp. 411-447. doi:10.1017/S1464793101005735.

Of cows and sweet potatoes

The sweet potato Ipomoea batatas has been used throughout the world as a food source for hundreds of years. Byproducts used as animal feed as a result of sweet potato processing include cannery wastes and sweet potatoes culled during the packing process due to damage, off size or oversupply.

The Veterinary Record [1,2] and the Guardian [3] recently discussed an incident in which six cows died as a result of consuming sweet potatoes. As far as is known this is the first recorded case of sweet potato poisoning in animals in the country. Five days before the first death, the cows had been fed 7 kg sweet potatoes per head per day. The sweet potatoes used were considered unfit for human consumption due to bruising. Examination of the remaining tubers showed the presence of the fungus Fusarium solani, amongst other species, on the skins and broken surfaces. The cows died over a period of four days, following signs of rapidly progressive dyspnoea. The deaths occurred within hours of the first respiratory symptoms. Necropsy examination showed severe interstitial pneumonia with extensive interlobular emphysema. On the basis of the evidence gathered, ipomeanol toxicity due to consumption of mould-damaged sweet potatoes was believed to be responsible for the deaths of the cows [4].

Over the years, reports from the USA, Japan, Australia and Brazil have implicated sweet potatoes in the deaths of cattle from a pulmonary disease known variously as pulmonary oedema, pulmonary adenomatosis, acute bovine pulmonary emphysema and atypical interstitial pneumonia as a result of eating mould-damaged sweet potatoes. The sweet potato is one of several plants able to form stress metabolites (also referred to as abnormal metabolites or phytoalexins) when subjected to an injurious stimulus which could take the form of mechanical injury, insect invasion, exogenous chemicals and microbial pathogens such as fungi. Several species of fungi, including F. solani and Ceratocystis fimbriata, have been found to stimulate the sweet potato to produce toxins. These toxins, 3-substituted furans, are hepatotoxins and pulmonary toxins, and are products of the sweet potato tissue, rather than of the fungus. The pulmonary toxins can cause lesions in the lung tissue of cattle, rats, rabbits and guinea pigs. These pneumotoxins, referred to as lung oedema factors include 1-ipomeanol, 4-ipomeanol, 1,4-ipomeanol, 1,4-ipomeadiol and ipomeanine, and are responsible for the acute pulmonary oedema and emphysema observed following consumption of Fusarium-infected sweet potatoes. Although the toxicity of damaged sweet potatoes is well-documented in cattle, a case of pigs dying from sweet potato poisoning has also been reported in Papua New Guinea [5]. Th effects of these sweet potato toxins on humans are not known; there is at present growing interest in the use of 4-ipomeanol as a potential prodrug for P450-directed gene therapy of liver and brain cancers.

There have been no reported cases to date of acute human poisoning following the consumption of sweet potatoes containing either hepatotoxins or lung toxins. Nevertheless, it is important to only select undamaged sweet potatoes for both human and animal feeding. Some reports suggest that neither baking nor boiling eliminates the toxins. Every effort, should, however, be made to maintain conditions to prevent these toxic metabolites from forming in the first place.

References
[1] Ipomeanol poisoning in cattle fed sweet potatoes. Veterinary Record (2007) 161:771-774.
[2] Mawhinney I, Woodgear N, Trickey S, Payne J. Suspected sweet potato poisoning in cattle in the UK. Veterinary Record (2008) 162 (2):62-63.
[3] Meikle, J. Six cows killed by sweet potato poisoning. The Guardian (Tuesday January 15, 2008). Accessed 21 January 2008. http://lifeandhealth.guardian.co.uk/food/story/0,,2240987,00.html
[4] Veterinary Laboratories Agency Monthly Surveillance Report October 2007. Accessed 21 January 2008. http://www.defra.gov.uk/corporate/vla/science/documents/end-survreport-1007.pdf
[5] Low SG, Grant IM, Rodoni B, Bryden WL. Sweet potato (Ipomoea batatas) poisoning of pigs in Papua New Guinea. New Zealand Veterinary Journal (1993) 41 (4): 218.

Suggested reading
Poore MH, Rogers GM, Ferko-Cotten BL, Schultheis JR. 2000. Sweet potatoes and associated byproducts as feeds for beef cattle. In Food waste to animal feed. Westendorf MC (ed), Iowa State University Press, Ames, Iowa, USA, pp. 163-183.
Wilson BJ, Burka LT. 1983. Sweet potato toxins and related toxic furans. In Handbook of natural toxins. Volume 1. Plant and fungal toxins. Keeler RF, Tu AT (eds), Marcel Dekker, New York, USA, pp. 3-41.
Woolfe, JA. 1992. Sweet potato: an untapped food resource. Cambridge University Press, UK, 659 p.

To search the VetMed Resource database for records on sweet potato poisoning use the terms (poisoning:de and sweet potatoes:de)

Northern Circumpolar Soil calendar 2008

Supporting the International Polar Year, March 2007 to March 2009 (two years are needed to cover all the seasons in northern and southern hemispheres), the European Union have published a rather smart 2008 calendar on Northern Cirumpolar Soils (9MB pdf).
Each month is dedicated to a different soil type, for example January covers Cryosols (from the Greek, kraios, meaning cold or ice). A distribution map, centred on the north pole, shows the approximate location of each soil type. In addition, a soil profile and a brief description of the soil are provided.      

The Nutrition Delusion

Sorry to harp back to Gary Taubes' Diet Delusion again. I make no pretence at having read the book, just Taubes' own 'teaser' in New Scientist last week. Rather than be 'teased' by the 'comment & analysis' piece, I have been left somewhat annoyed.

To accuse the nutrition profession of creating 'a field of clinical medicine that functions more like a religion than a science' is to shoot down all the hard work that nutritionists around the world have been doing to wrestle the science of nutrition out of the exclusive hands of the medical field, while trying to persuade those medics to adopt a greater understanding of nutrition and incorporate this into their pharmacologically dominated practice.

As this article was winging its way to my desk last week, I was enjoying a very interesting discussion with Dr Barrie Margetts, who runs Southampton University's Masters course in Public Health Nutrition. This is the field that brings the latest fundamental science from the laboratory to the populous and feeds back the results of the interventions that have been tried. Or at least that's the theory. Margetts and his colleagues in public health nutrition are not practising a straightforward science. There was a time and a place, briefly, when experimental human nutrition was approached in much the same way we study animal nutrition today. But we don't like to talk about that nowadays.

The problem is people.

Joined up science

Usually, when the urge to blog comes over me, I can wait until the urge goes away and bothers someone else, or until enough time has passed to make the reason for the blog obsolete.

On this occasion, however, the urge hasn't gone away and I hope you'll forgive me for alerting your attention to an issue of New Scientist that you've probably already recycled.

In last week's (19th January) edition, there were 3 clippings that I didn't just collect, but stapled together. And they have been distracting me ever since.

Omega-3 fatty acids – what have we learned?

It’s well known that omega-3 fatty acids are crucial to the development of the brain. Animal studies have suggested that a specific fatty acid, docosahexaenoic acid (DHA), plays a role in the development of cognitive abilities. So will taking extra DHA as a child make you cleverer? A paper in CAB Reviews by Carol Cheatham at the University of Kansas Medical Center looks at the evidence from both animal and human studies.

Animal studies have shown clearly that DHA deficiency affects memory and learning, and that providing extra DHA can restore these abilities to some extent. However, in humans, fewer than half the randomised clinical trials report effects on cognition from DHA.

Babies born early miss out on the final weeks of DHA they would receive from their mothers via the placenta. Studies show that providing preterm babies with DHA does improve memory and attention relative to controls. However, for babies born at term, providing extra DHA has not given the same clear outcome, with different trials giving different results.

Cheatham looks at three possible reasons. One is that the doses of DHA may not have been high enough to work. Also, the trials used a wide variety of measures of learning and memory. Looking at more specific measures of cognition could give less mixed results. Few studies have looked at the long- term impacts, and so studying children some years after taking DHA supplements in more sophisticated tests may reveal differences.

The paper,Omega-3 fatty acids and the development of cognitive abilities: a review of DHA supplementation studies, by Carol L. Cheatham appears in CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2008, 3, No. 001.

The new HIV or just an outbreak of boils?

An aggressive and drug resistant version of the hospital superbug MRSA is spreading through the gay community in San Francisco. The infection rate is doubled in areas with a high gay population compared to the whole of the city. A study in Annals of Internal Medicine raised the alarm but some newspapers were way over the top reporting this comparing it to the HIV epidemic. Although the outbreak is worrying because of the high drug resistance of the MRSA strain involved and the HIV status of the community no way is it comparable to HIV. The infections are skin infections and there are still drugs to treat them as well as surgical methods.

Cryptosporidium and Giardia in drinking water: not just a problem for industrialised countries

Dr. Lucy Robertson, a speaker at the 8^th Central American and Caribbean Congress on Parasitology and Tropical Medicine 2007, points out that as countries strive to improve their standards of public health, we should find it intolerable to accept the transmission of these infections via drinking water anywhere.

 

Of the parasitic infections with a global impact, both cryptosporidiosis and giardiasis come relatively low on the list. However, acute infections with both can be extremely debilitating in the short-term, the paucity of chemotherapy for cryptosporidiosis can mean that it may be a fatal infection for the immunocompromised, and refractory giardiasis can be associated with prolonged morbidity, even after apparent recovery from the infection. Both infections most surely contribute to the global death toll from diarrhoeal infections, particularly in children. Currently this stands at 2.2 million children annually; one every 14 seconds.

 

The high excretion rate, low infective dose, and robust transmission stages of both parasites lend themselves to dissemination by drinking water, and there have been many extensive waterborne outbreaks of both parasites in which hundreds or thousands of individuals have been infected. On the whole, outbreak reports are usually from industrialised countries (Karanis et al, 2007). For example, in 1993 over 400,000 people developed cryptosporidiosis in Milwaukee, USA due to contamination of the drinking water supply (MacKenzie et al, 1994) and, more recently, in 2004, in Bergen, Norway, over 1500 people suffered from giardiasis due to water supply contamination (Robertson et al, 2006). 

 

At the 8^th Central American and Caribbean Congress on Parasitology and Tropical Medicine* in Havana, Cuba (4^th - 7^th December 2007), various groups gave presentations concerning different aspects of cryptosporidiosis and giardiasis, but only one plenary session was devoted to the detection of these parasites in water and other environmental matrices.  YET many of the delegates come from countries or regions in which drinking water supplies are more vulnerable to contamination, or where water treatment is minimal: these populations are obviously at greater risk from these diseases, and, in addition, the exposed populations are often more likely to be susceptible to more severe symptoms from both infections. Though drinking water transmission must occur, for these communities cryptosporidiosis and giardiasis are rarely seen as a pressing problem and outbreaks go unreported.

There are various possible reasons for this situation, including:

where drinking water infrastructure is poor, both infections could be so widespread that outbreaks cannot be identified against background infections

persistent exposure has resulted in some degree of immunity amongst the adult populations in such communities.

Nevertheless, as countries strive to improve their standards of public health, we should find it intolerable to accept the transmission of these infections via drinking water anywhere.

 

Over 490 delegates attended the Congress, 290 from Cuba, and 202 from other countries, particularly Latin America, but also including Japan, Europe, Africa, and Central Asia, in an impressive programme organised by the Pedro Kourí Institute of Tropical Medicine in Havana. In my presentation I was attempting to describe the reasons for assessing water and food as vehicles for these infections, and the various methods and approaches by which this could be accomplished. By illustrating the web of interactions between water, food, parasites, and human health, I hoped to demonstrate that by having knowledge of contamination, suitable strategies could be implemented to reduce or eliminate these routes of transmission. The enthusiasm and dedication of the many delegates at the Congress was notable, but from the questions after my talk it was clear that to many of them the technical and political aspects of analysing water supplies for parasites seemed insurmountable. This is understandable; as the parasites cannot be cultured like bacteria, detection of both parasites in drinking water involves separating the individual transmission stages from the water. It is a costly procedure with multiple steps, including immunomagnetic separation and detection by immunofluorescent microscopy. Nevertheless, identification and interruption of transmission routes for these parasites is essential in their control, and with the 2015 Millenium Development Goals deadline approaching (MDG 4, 6 & 7 indicators are relevant here, see MDG progress chart), the time is ripe for global players to step in and ensure that drinking water supplies everywhere are parasite-free.

 

 

*The Central American and Caribbean Congress on Parasitology and Tropical Medicine is a biennial event: Cuba 2007 included 32 plenary sessions, and over 350 poster presentations, as well as 4 pre-congress workshops, 11 symposia, and 9 round table discussions. The next Congress is scheduled for 2009 in Costa Rica.

 

References:

1. Karanis, P., Kourenti, C. & Smith, H. 2007. Waterborne transmission of protozoan parasites: a worldwide reveiw of outbreaks and lessons learnt. J. Water Health 5(1), 1-38.

2. Mac Kenzie W.R., Hoxie N.J., Proctor M.E., Gradus M.S., Blair K.A., Peterson D.E., Kazmierczak J.J., Addiss D.G., Fox K.R., Rose J.B., & Davis, J.P. 1994. A massive outbreak in Milwaukee of Cryptosporidium infection transmitted through the public water supply. N. Eng. J. Med. 331(3), 161-7.

3. Robertson L.J., Hermansen, L., Gjerde, B.K., Strand, E., Alvsvåg, J.O. & Langeland, N. 2006. Application of genotyping duirng an extensive outbreak of waterborne giardiasis in Bergen, Norway during autumn and winter 2004. Appl Environ Microbiol 72, 2212-2217.

 

4. UN MDG progress chart, indicators for MDG 4, 6 and 7:  namely reducing under 5 child mortality by 2/3, the combat of malaria, HIV/AIDS and other diseases, halving the proportion without improved drinking water.

Editors note:

1. To view relevant Global Health content which is freely available on Google, use this link:

http://www.google.com/coop/cse?cx=011480691189790707546%3Azwixxwtzvyu&hl=en

 

Then enter this search:  (giardiasis or cryptosporidiosis) AND outbreaks

2. CABI will publish in August 2008 a new book, Giardia and Cryptosporidiosis, edited by M. G. Ortega-Pierres et al. Read more at: http://www.cabi.org/bk_BookDisplay.asp?PID=2109

Dr. Lucy Robertson is based at:

Seksjon for Parasittologi

Institutt for mattrygghet og infeksjonsbiologi

Norges veterinærhøgskole

PO boks 8146 Dep

0033 Oslo

NORWAY.

 

Biofuel – the burning issues

The development of biofuel has been hailed as a sustainable way to combat dependency on declining oil reserves, but a new study suggests there are substantial obstacles to large-scale deployment of biofuels. It is still an open question whether biofuel can meet a significant proportion of the world’s energy needs, say John Fike and co-authors in a paper in CAB Reviews. There are numerous practical questions about biomass systems, from feedstocks to logistics to pretreatment/process technologies, to be addressed. While policies aimed at reducing carbon emissions may support biofuel, other environmental impacts are also of concern, say Fike and his colleagues at Virginia Polytechnic Institute and State University.

The cost of hauling the feedstock to the refinery is a key issue, and so a high proportion of farms within a given radius of the refinery would have to commit to producing the feedstock, as a need to transport the feedstock over long distances would make bioenergy production uneconomic. The distance of the refineries from the energy user is also an important factor. There are many logistic and socio-economic issues that will need to be resolved along with the purely technical issues, say the Virginia Tech team.

Policy is critical, and if US policies were to create a value for carbon sequestration, this would of course change the economics of bioenergy production. Tax levels on biofuel relative to fossil fuel are another central issue. Fike and his co-authors question whether the US government would allow a switch from food to bioenergy production to allow large increases in food prices, as some models have predicted. Some residents may oppose the dramatic industrialisation of the countryside that comes with bioenergy, but others may feel that this is a price worth paying for renewable energy.

The paper, Challenges for deploying dedicated, large-scale, bioenergy systems in the USA by John Fike, David Parrish, Jeffrey Alwang and John Cundiff appears in CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources2, No. 064, 28 pp.

Review of 2007

Happy New Year and a big thank you to all those who subscribe or read our blog.

It was a good 2007 for the hand picked ... and carefully sorted with a full calendar year of blogging under our belt, turning 1 year old on 2nd November. We posted 167 articles on a variety of topics and had one of our posts, "Bluetongue virus:knocking at the door" by Robert Taylor, nominated for consideration towards the new edition of the Science Blogging Anthology, "Open Laboratory 2007".

Please read on for a monthly breakdown of all our posts.