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Biological water quality – part 1

Watch Professor Jo Cable describe waterborne pathogen, diseases and other kinds of widespread infections are transmitted via contaminated water.
Welcome to the first of two talks on biological water security. My name is Jo Cable, and I’m based in the School of Biosciences at Cardiff University. There are three main categories of biological threats to freshwater– parasites, invasive species, and population explosions of animals or plants. And of course, these three categories are not mutually exclusive. So invasive species– for instance, the invasive signal crayfish can bring with it pathogens when it’s introduced into new environments. In the case of the signal crayfish, it can bring in a disease causing crayfish plague, which is particularly problematic for endemic species. All of these three categories of biological threats can interact together, and they also can interact within changing environments or conditions.
So the challenge, then, is water quantity and quality affecting waterborne diseases. Around the world, 2.5 billion people lack access to improved sanitation. And 780 million people lack access to purified water source. As a result, water-related diseases cause 3.4 million deaths every year as a result of poor sanitation and hygiene. And to put this into very stark terms, every 90 seconds around the world, somewhere a child dies from a waterborne disease. And the third leading source of childhood death is diarrhoea caused by waterborne pathogens. But it’s not just humans that are affected by waterborne pathogens. Our animals, our farmed animals, and certain wildlife can also suffer significantly from waterborne diseases. So what are the threats and problems?
Well, it really is a diversity of pathogens that are causing these issues, ranging from viruses to worm-like organisms called helminths. Many of them are cryptic, and some of them are unidentified species. So finding these very small parasites, most of which are microscopic. And very small doses of these pathogens can cause my life threatening diseases to humans and/or animals.
The ways in which we can acquire these pathogens can be broadly categorised into four different groups. Firstly, we can acquire these waterborne pathogens by consuming contaminated water or eating food that’s been contaminated in this way. We can inhale infective agents. We can acquire pathogens by dermal contact– so parasites in water can penetrate to our skin or mucous membranes. And finally, we can acquire pathogens from biting insect vectors, vectors which either breed in water or some other part of their biology is dependent on being near water. So lots of different routes at which we can acquire these pathogens. One particular waterborne pathogen which you might have heard of is called Cryptosporidium.
It’s a protozoan parasite, otherwise known as a blue-marble pathogen because it occurs in so many countries around the world. Almost like the sort of blue veins of a cheese, making its way in lots of different environments. It occurs in domestic animals, and animals infected Cryptosporidium can release a large number of infective stages, or oocysts, into faecal matter, which is then washed into water bodies. And even though the pathogen is exposed to water treatment, certainly in developing countries, the parasite is resistant to chlorine. And filtration is not always successful in removing this small pathogen. We do know that it is destroyed by UV, so that is an effective way of taking it out of our drinking water.
But it’s a really expensive way of actually treating the water. So in developed countries, the presence of Cryptosporidium as a constant threat makes our water processing very expensive. And because we don’t have UV facilities on all of our water supplies, it can actually appear in the water supply. And for those individuals who are immunocompromised or sick in advance, this can prove potentially fatal. In developed countries, a large number of children on a global basis are affected by this pathogen. And sadly, over 200,000 die each year due to this pathogen.
So to summarise this example of a waterborne pathogen– Cryptosporidium– which occurs in both temperate and tropical climates, it infects both humans and animals and is especially dangerous for humans who are already sick, and might have HIV or some other pathogen. They might be malnourished. And then this makes them more vulnerable to the effects of Cryptosporidium infection. It also has a massive economic impact on our farming. And these animals can produce large numbers of parasites that are shared in faeces. And because the parasite has a very thick, protective outer shell, this promotes its survival in the environment and makes it very difficult for us to get rid of the pathogen. So for instance it can persist in chlorinated pools.
And there have been various outbreaks, particularly in the states, of Cryptosporidium, people acquiring the pathogen from swimming pools. So it’s very much an opportunistic pathogen. And often when you have shortages in water treatment, problems of sanitation, you then have epidemics of this disease. So that’s just one human pathogen which some of you might have heard of before. Water pathogens also great risk to our livestock– I’ve just included a few more examples here. Giardia, another protozoan pathogen like cryptosporidium. You’re probably familiar with lots of bacterial infections in water. And we can also have a lot of incidents of worms, parasitic worms, being transmitted in water.
In the lifecycle of one particular pathogen, a liver fluke, otherwise known as fasciola, is shown in this life cycle. Important point I want to make here is that animals infected with these pathogens can release large numbers of the pathogen in faecal matter. And although this may not go directly into water, often with runoff it very quickly makes its way into freshwater. And this is a huge problem for infections– infections both of animals, but also humans too. And of course, parasites in agriculture and wild fish stocks is really problematic. You have some parasites which are very large and obvious.
You have other pathogens which have given sort of rather general names like black spot, and there many, many different diseases that cause black spot in fish. This is rather ambiguous. And then you can have whole outbreaks of disease– large, mass mortality of fish stocks. And even then it becomes really problematic to actually identify the cause of this. And some of these parasites are amazing to look at, but also quite horrific. Here we have the classic example of the parasite crustacean organism that actually attaches to the fish’s tongue and takes over the tongue. A rather alien-like creature. A fungal like organism here that’s literally taken over the entire tail of the fish– these mycelial growths.
And then a very large parasite occurring on large numbers on the fish. So something hugely problematic and a major cause of loss of animals within agriculture. Parasites really are problem on a global level. There are lots of abiotic and biotic factors aside from the parasites and the host themselves that will infect the host-parasite interaction. Weather and climate, particularly, has huge impact. Runoff of soil contaminated with parasites into water bodies can alter the distribution of parasites, also vectors. And droughts can create transmission hotspots, where you have aggregation of parasites in waters. Other factors associated with global change– urbanisation, water connectivity, and pollution– are also important.
And these interplay with the natural, spatial and temporal variation that we see in the presence of waterborne pathogens. And next time that I talk, I’m going to focus on this spatial and temporal variation of pathogens.
In the meantime, do read yourself a little bit about waterborne pathogens. And until then, I look forward to talking to you next time.

In this video, Professor Jo Cable explains how waterborne pathogen, diseases and other kinds of widespread infections, reach people and animals through contact with contaminated water.

These are some of the largest causes of illness and even death across the world.

Many organisms present in freshwaters can cause illness and even death when consumed by humans and animals. These organisms, mainly bacteria, protozoa, virus and algae, enter into streams, rivers and lakes either naturally, or during the release of improperly treated sewage or waste waters.

Biological quality is an important factor to determine the quality and therefore security of water. It’s more important than chemical quality in terms of direct effect on human health. Waterborne parasites, in particular, are a serious concern across the world.

They’re incredibly abundant and diverse, to the extent that added together their biomass is equivalent to that of all birds on our planet.

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The Challenge of Global Water Security

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