Parasite Problem for Creationists

Stone Age worm egg hints at origins of modern scourge - health - 20 June 2014 - New Scientist

News that the earliest known evidence of the parasitic flatworm which causes schistosomiasis in human has been found, reminds me how rarely we see creationist pseudo-scientists discussing parasites, least of all parasites on humans. Maybe they are just sensitive to the subject for understandable reasons given their generally parasitic lifestyle but that would require a social conscience. It's much more likely that it's impossible to fit them into a biblical model where a magic, benevolent god created everything for humans because it loves us.

Parasites, by definition, take from their hosts but give little or nothing in return. They also often make their hosts sick in the process.

As for schistosomiasis, according to the World Health Organization:

Symptoms
Intestinal schistosomiasis can result in abdominal pain, diarrhoea and blood in the stool. Liver enlargement is common in advanced cases, and is frequently associated with an accumulation of fluid in the peritoneal cavity and hypertension of the abdominal blood vessels. In such cases there may also be enlargement of the spleen.

The classic sign of urogenital schistosomiasis is haematuria (blood in urine). Fibrosis of the bladder and ureter, and kidney damage are sometimes diagnosed in advanced cases. Bladder cancer is another possible complication in the later stages. In women, urogenital schistosomiasis may present with genital lesions, vaginal bleeding, pain during sexual intercourse and nodules in the vulva. In men, urogenital schistosomiasis can induce pathology of the seminal vesicles, prostate and other organs. This disease may also have other long-term irreversible consequences, including infertility.

The economic and health effects of schistosomiasis are considerable. In children, schistosomiasis can cause anaemia, stunting and a reduced ability to learn, although the effects are usually reversible with treatment. Chronic schistosomiasis may affect people’s ability to work and in some cases can result in death. In sub-Saharan Africa, it has been estimated that more than 200,000 deaths per year are due to schistosomiasis.

WHO Fact sheet N°115 (Updated February 2014)

The parasite enters the human body when the laval form of the parasite penetrate the skin when people are in contact with infected water. The worms then take up residence in various tissues where the females lay eggs. Some of these are passed out in urine and faeces to contaminate water whilst some remain in blood vessels where they cause blockages and immune responses responsible for damage to the organs. The eggs hatch in water and are ingested by water snails where they mature into the water-borne lava to infect humans again.

By far the commonest locations for this cycle to become established is in the tropical areas of the world where crop irrigation systems creates standing water, such as paddy fields, creating ideal conditions for the water snails to live as intermediate hosts and where people work often knee-deep in water. Transmission can occur in natural pools but human agriculture has created by far the commonest means of transmission.

The Tell Zeidan site is about 48 feet high at its tallest point and covers about 30 acres. It sits in an area of irrigated fields at the junction of the Euphrates and Balikh Rivers in what is now northern Syria.

Credit: Gil Stein, Oriental Institute, University of Chicago

The team led by Piers Mitchell of Cambridge University, UK, which discovered the fossil worm eggs, found them when they examined the sediment from beneath the pelvises of 26 skeletons dated to between 6500 and 6000 years old from Tel Zeidan. The fossil egg was found under a 6200 year-old specimen. The previous oldest evidence of the disease in humans was in a 5200 year-old Egyptian mummy.

Of course, it's probably a long stretch to read too much into one egg found under one body, certainly so far as the origin of the water in which the transmission occurred is concerned, though it is evidence that humans at that time and in that location suffered from the parasite. However, given the generally arid conditions in northern Syria away from the Euphrates and Balikh Rivers themselves, hence the need to irrigation, it is highly likely that the few areas of standing water able to maintain a population of water snails would have been man-made floods. This area of the Fertile Crescent was where crop irrigation was invented about 1000 years earlier. The evidence for that is the archaeological evidence for water-hungry crop plants.

The spread of this parasite probably coincided with the spread of crop irrigation as human society developed from hunter-gatherers into agriculture and urbanized settlements, illustrating how a changed environment creates opportunities for other forms of life, and not always to the benefit of those who changed the environment. Before then it was already in Africa, and Southeast Asia. Genetic and cladistic studies on the various species of Schistosoma genus as well as the snails it uses as intermediate host suggest it evolved in Gondwanaland between 140 million dnd 70 million years ago probably as a parasite on hippopotami, which were present in Southeast Asia in the Cenozoic era. It may then have spread to rodents in Southeast Asia. When humans created the right conditions the parasite crossed the species barrier into us and now affects some 210 million people worldwide, being second only to malaria in it economic and health impact.

And this is all perfectly well explained, even predicted, by the genetic theory of evolution.

Is it worth asking a creationist to try to fit schistosomiasis into their model of creation by an omnibenevolent god who made everything just for his special creation, humans? Probably not, but I will anyway.

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