Leishmania parasites: neglected tropical killers

Later this year I will be visiting The Gambia in West Africa to work on a GirlGuiding community project. Before I go I will need to have some vaccinations to protect me from several of the diseases found there. Unsurprisingly, this has rekindled my interest in tropical diseases. This week, I have strayed from my usual subjects to write about the leishmaniases, a group of tropical diseases found across Africa, Asia and the Americas. Included in the World Health Organisation’s (WHO) list of Neglected Tropical Diseases, the leishmaniases are a big burden on public health services in many countries, and were responsible for an estimated 50,000 deaths worldwide in 2010 alone.

Leishmaniases are caused by parasitic single-celled organisms of the genus Leishmania. The parasites are carried between mammal hosts by several species of blood-sucking sandflies. The parasites live within the mouthparts of the sandflies and can be transmitted to mammals when the sandflies bite. The parasites exist in different forms in sandflies and mammalian hosts. In the sandfly, Leishmania cellsbecome promastigotes and move around the insect gut using string-like structures called flagella. Within a mammal host, the parasites “hide” within host immune cells (called macrophages) and lose their flagella to become amastigotes.

Leishmania parasite lifecycle requires sandfly and mammalian hosts. This image is a work of the Centers for Disease Control and Prevention (US Federal Government). The image is in the public domain (via Wikipedia).

The Leishmania parasite lifecycle requires both sandfly and mammalian hosts. This image is a work of the Centers for Disease Control and Prevention (US Federal Government). The image is in the public domain (via Wikimedia Commons).

In more minor Leishmania infections, the parasites infect the skin, leading to sores and ulcers. Usually the infection is confined to the area around the insect bite, and clears up either by itself or in response to treatment. In some cases, the parasites can spread and cause sores on the skin in other parts of the body. The parasites can also move to the linings of the nose and throat and cause permanent tissue damage. In the second, more serious form of leishmaniasis, the parasites infect internal organs including the spleen and liver. The infection is usually fatal if left untreated.

Ulcer formed due to Leishmania skin infection.

Ulcer formed due to Leishmania skin infection.

No vaccines against Leishmania are currently available, so control of the diseases focuses on reducing the risk of people being bitten by infected sandflies. Several strategies are used including: the early diagnosis and treatment of disease cases, control of sandfly populations using insecticides and bed nets, monitoring of disease cases and control of populations of other host mammals e.g. dogs and rats (1). Efforts are also being made to educate local communities about the diseases and how they can alter their lifestyles to reduce their risk.

Unfortunately, our understanding of where the leishmaniases are found is poor, so it is difficult to target control efforts to those most at risk. In a research paper recently published in eLife, researchers compiled a database of disease cases across the globe from many sources including published literature, and online reports. The spread of diseases can be affected by environmental factors, such as climate, and by socioeconomic factors such as poverty, or whether an area is rural or urban. The researchers brought together disease case data with environmental and socioeconomic information and used statistics to create global risk maps for the leishmaniases.

The global risk maps highlight areas where leishmaniases are common, and also reveal areas at high risk that currently have few or no reported cases. This could be because the diseases are not present, or because cases are not being reliably reported. The information provided by the global risk maps can help target disease monitoring to at risk areas, identify target areas for disease control and help inform estimates of the burdens that may fall on public health systems in future.

Fortunately for me, leishmaniases are rare in The Gambia so my risk is minimal. Hopefully, the information provided in the risk maps can help to reduce the risks to people in regions that aren’t so lucky.


1) World Health Organisation (WHO) Media Centre. Fact Sheets http://www.who.int/mediacentre/factsheets/fs375/en/ (retrieved 17/07/14)

2) Pigott et al (2014) Global distribution maps of the leishmaniases. eLife

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Sabotage of plant cell communication by invading bacteria

Leaf speck on a tomato leaf caused by Pseudomonas syringae infection. Image by Alan Collmer via Wikimedia Commons (CC0).

Leaf speck on a tomato leaf caused by Pseudomonas syringae infection. Image by Alan Collmer via Wikimedia Commons (CC0).

To protect themselves from infection by disease-causing microbes, plants have systems that detect potentially harmful microbes and activate defence responses. Disease-causing microbes can overcome these defences by producing proteins called effectors that can enter host plant cells and disrupt them. Understanding what these effectors do in host plants could be useful for the development of more disease-resistant crop plants. Unfortunately, the roles of many effector proteins are not yet understood.

One of the ways effector proteins can interfere with plant defence responses is to prevent the relay of danger messages from the site of microbe detection at the plasma membrane to other locations in the cell. For the signal relays to function, the various protein components need to be located in the right places in the cell (plasma membrane, cytoplasm, nucleus, vacuole etc.). The cytoskeleton, consisting of filaments of the protein actin, is required for this organisation and moves proteins contained within (or on) small membrane-bound structures called vesicles. Continue reading

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Making waves at the Plant Calcium Signalling meeting

Last week I went to the Plant Calcium Signalling Meeting in Münster, Germany. I really enjoyed the meeting and it was a great opportunity to get an update on the most recent research in the area.

I have a guest blog on Annals of Botany blog about my personal highlights of the conference click the link to read it.

If you haven’t seen it already, read the article I posted earlier this week about a new drought-tolerant barley variety that has been developed by some of my colleagues at the John Innes Centre in collaboration with researchers at the University of Jordan.

And don’t forget that the Organism of the Month here at Plant Scientist is the poppy. There are still loads in flower in the UK at the moment to take a look if you can. If you want to know more read Kirsty Jackson’s article.


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Why we should all be interested in drought-tolerant barley

Image by Gerste Ähren (licenced under CC BY-SA 3.0)

Image by Gerste Ähren (licenced under CC BY-SA 3.0)

Last week, it was announced that researchers from the John Innes Centre, UK and the University of Jordan have developed a variety of barley that is four times more drought-tolerant than other barley varieties. Why do we need drought-tolerant crops, and what is so significant about this barley?

All plants need water to grow. Consequently, agriculture is highly dependent on water and accounts for 70% of global water consumption. This is a massive amount of water. To put it another way, it takes around 2000-3000 litres of water to produce the food that one person typically eats in a single day! In many regions, not enough rain falls to provide sufficient water to crops and the fields have to be irrigated with water taken from rivers and underground sources. Continue reading

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Guest Post. Poppies: A blessing, a curse and a moment of reflection

Papaver dubium in Norfolk, UK. Photo by the author.

Papaver dubium in Norfolk, UK. Photo by the author.

A week early, the red poppy is the Organism of the Month of July here at Plant Scientist. I didn’t want to delay the publication of this post since there are loads of red poppies in flower in Europe at the moment!

By Kirsty Jackson (@kjjscience)

At this time of year poppies seem to spring out of anywhere and everywhere they can. In the last few weeks I have seen them in gardens, motorway central reservations and even poking out of Norwich’s medieval city wall.

Opium poppy (Papaver somniferum). From Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885

Opium poppy (Papaver somniferum). From Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885 (via Wikiemedia Commons).

Humans have used poppies in food, medicines and beauty treatments for around 6,000 years. The opium poppy (Papaver somniforum) was widely used by the Greeks, Romans and even thought to be used by Neolithic tribes. When looking upon the pretty flower of the opium poppy, you could be forgiven for thinking that it is harmless. In fact, the opium poppy has been both a blessing and curse for humanity.

During the ripening of the opium poppy seed capsule, the head produces a milky sap, which is the source of the drug opium. In the 18th Century, China suffered greatly due to the addictive properties of opium. Britain, in an attempt to gain trade from China, supplied the Chinese with opium (from Bengal), despite resistance from the Chinese government. The effects of opium began to destabilise China and enabled the British to prosper in Opium Wars of the mid-19th Century. It was at this time (~1842) that Hong Kong became a colony of the British Empire and it was not returned to China until 1997. Continue reading

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The GM debate is distracting us from the real issues in agriculture

Image credit: Photograph by Dako99 (CC BY-SA 3.0)

Image credit: Photograph by Dako99 (CC BY-SA 3.0)

The debate over the use of genetically modified (GM) crops has been going on for a long time. Despite the controversy, GM crop production has grown rapidly since 1996, and GM crop varieties are now planted on 3.5% of the World’s total agricultural land (1). In an article published his week in PLOS Biology, Ottoline Leyser argues that this debate is distracting us from addressing the real challenges facing modern agriculture: global food security and environmental sustainability (2).

Leyser starts by discussing how GM is considered by many to be the epitome of all that’s bad in modern agriculture: the dominance of profit-driven multinational corporations, high-intensity monoculture farming and the accompanying use of large quantities of environmentally-damaging chemicals. As a plant scientist and nature-lover, I am also concerned about these farming practises. However, as Leyser points out, they have nothing to do with GM technology. It is a situation that was reached long before GM-crops were first grown commercially and is prevalent all over the world, including in the EU, where GM-crops have never been widely grown. Continue reading

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The food, magic and medicine of the elder tree

Elderflowers in Norfolk, UK. Image by the S. Shailes. Licenced under CC BY-SA 4.0.

Elderflowers in Norfolk, UK. Image by S. Shailes. Licenced under CC BY-SA 4.0.

One of the advantages of living in a small, green city with easy access to the countryside is that there are quite a few opportunities to forage wild things to eat. As a relative newcomer to a small city (I grew up in London) I’m only just starting to explore these opportunities. This week I used some flowers from some local elder trees to make elderflower cordial. It is only fitting that I feature the elder (Sambucus nigra) as the Organism of the Month.

The S. nigra is a deciduous shrub or small tree native to Europe and Asia (1). There are several other very closely-related species native to Asia and North America, such as the Mexican elderberry Sambucus mexicana. S. nigra is common in the UK and is found in woodland and hedgerows. Elder wood is soft, so not well-suited for construction, but is used to make traditional European flute instruments. Continue reading

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