Friday, 19 March 2021

Malevolent Designer News - Making the Leishmania Parasite Better at Making You Sick

Leishmania infantum life cycle

Dogs infected with Leishmania parasites smell more attractive to female sand flies | Lancaster University

Here is one of those papers that leave intelligent [sic] design creationists with two choices: they can either pretend that a designer who can come up with these sorts of designs is not really malevolent and being ever-more inventive in its endeavour to make us sick, or they can absolve it of any culpability by accepting that these things are the inevitable result of a purely natural, amoral, undirected natural process, operating under nothing more than the laws of physics and chemistry.

Cutaneous leishmaniasis ulcer
Credit: Layne Harris
Wikipedia
It is the discovery that female sand flies, Lutzomyia longipalpis, which are the main vectors for transmitting the parasite that causes Leishmaniasis to humans, are more attracted to dogs which are carrying the parasites than those which are healthy, so increasing the probability of infecting humans.

The discovery is the work of two scientists, Professor Gordon Hamilton and Monica E. Staniek, of Lancaster University.

The new release from Lancaster University explains:
Dogs infected with the Leishmania parasite smell more attractive to female sand flies than males, say researchers.

The study published in PLOS Pathogens is led by Professor Gordon Hamilton of Lancaster University.

In Brazil, the parasite Leishmania infantum is transmitted by the bite of infected female Lutzomyia longipalpis sand flies.

In this study we showed that infected dog odour is much more attractive than uninfected dog odour to the female sand flies. Only the females can transmit the pathogen and male sand flies, which do not transmit the parasite, are not affected by the changed odour.

This clear-cut difference in attraction of female and male sand flies suggests that the females are preferentially attracted by parasite infected hosts and this could lead to enhanced infection and transmission opportunities for the parasite.

Domestic dogs are the reservoir of infection, therefore understanding how the infection affects the attractiveness of dogs to the insect vector is important in understanding the epidemiology of the disease and offers opportunities for new control and diagnostic methodologies.

Professor J ames G. C. Hamilton, Lead author
Lancaster University
Globally over 350 million people are at risk of leishmaniasis, with up to 300,000 new cases annually. In Brazil alone there are approximately 4,500 deaths each year from the visceral form of the disease and children under 15 years old are more likely to be affected.

Leishmania parasites are transmitted from infected dogs to people by sand flies when they bite. Visceral leishmaniasis affects the internal organs and is fatal if not treated.

As only female sand flies transmit the parasite, researchers wanted to understand if infection made dogs more attractive to the insect.

Professor Gordon Hamilton of Lancaster University said: “In this study we showed that infected dog odour is much more attractive than uninfected dog odour to the female sand flies. Only the females can transmit the pathogen and male sand flies, which do not transmit the parasite, are not affected by the changed odour.

“This clear-cut difference in attraction of female and male sand flies suggests that the females are preferentially attracted by parasite infected hosts and this could lead to enhanced infection and transmission opportunities for the parasite.”

The researchers had previously found that dogs infected with Leishmania parasites smelled different compared to uninfected dogs.

Professor Hamilton said: “Domestic dogs are the reservoir of infection, therefore understanding how the infection affects the attractiveness of dogs to the insect vector is important in understanding the epidemiology of the disease and offers opportunities for new control and diagnostic methodologies.”
The research is published open access today in PLOS Pathogens:

Abstract


Globally visceral leishmaniasis (VL) causes thousands of human deaths every year. In South America, the etiologic agent, Leishmania infantum, is transmitted from an infected canine reservoir to human hosts by the bite of the sand fly vector; predominantly Lutzomyia longipalpis. Previous evidence from model rodent systems have suggested that the odour of infected hosts is altered by the parasite making them more attractive to the vector leading to an increased biting rate and improved transmission prospects for the pathogen. However, there has been no assessment of the effect of Le infantum infection on the attractiveness of dogs, which are the natural reservoirs for human infection. Hair collected from infected and uninfected dogs residing in a VL endemic city in Brazil was entrained to collect the volatile chemical odours present in the headspace. Female and male Lu. longipalpis sand flies were offered a choice of odour entrained from infected and uninfected dogs in a series of behavioural experiments. Odour of uninfected dogs was equally attractive to male or female Lu. longipalpis when compared to a solvent control. Female Lu. longipalpis were significantly more attracted to infected dog odour than uninfected dog odour in all 15 experimental replicates (average 45.7±0.87 females attracted to infected odour; 23.9±0.82 to uninfected odour; paired T-test, P = 0.000). Male Lu. longipalpis did not significantly prefer either infected or uninfected odour (average 36.1±0.4 males to infected odour; 35.7±0.6 to uninfected odour; paired T-test, P = 0.722). A significantly greater proportion of females chose the infected dog odour compared to the males (paired T-test, P = 0.000). The results showed that the odour of dogs infected with Le. infantum was significantly more attractive to blood-seeking female sand flies than it was to male sand flies. This is strong evidence for parasite manipulation of the host odour in a natural transmission system and indicates that infected dogs may have a disproportionate significance in maintaining infection in the canine and human population.

Author summary


Visceral leishmaniasis (VL) is a disease caused by the Protist parasite Leishmania infantum. In Brazil and other South and Central American countries, the parasite is transmitted by the bite of infected female Lutzomyia longipalpis sand flies. The disease leads to thousands of human deaths every year. Domestic dogs are the reservoir of infection therefore understanding how the infection affects the attractiveness of dogs to the insect vector is important in understanding the epidemiology of the disease. Golden Hamsters infected with Le. infantum are more attractive than uninfected hamsters to Lu. longipalpis however, it is not known if the attractiveness of infected dogs is similarly altered. In this study we showed that the odour of infected dogs is significantly more attractive to female sand flies, that can transmit the pathogen, than it is to male sand flies which can not. This clear-cut difference in attraction of female and males suggests that the females are preferentially attracted by parasite infected hosts and may lead to enhanced infection and transmission opportunities for the parasite.
Here we have another example of a parasite manipulating its host in a way which is advantageous to the parasite - making its odour more attractive to the parasite's vector species. According to Creationists, none of this happens by accident or even by the operation of natural laws, but is the result of deliberate design by a putative intelligent [sic] designer, who is one and the same as the supposedly all-loving god of the Abrahamic religions.

Interestingly too Leishmania infantum has one of those flagella that the Creationist inventor of the intelligent design notion, Michael J. Behe, made his name with by arguing, against the evidence, that it must have been designed by an intelligence because it is 'irreducibly complex'. So, in the fantasy world of Creationism, here we have an example of an organism that was supposedly deliberately designed and which looks just like it was designed for the sole purpose of killing people and making them suffer, with an added refinement to make it more likely that the sand fly vector will transfer it from the reservoir in domestic dogs to its intended victims - human beings.

For some, as yet unexplained reason, fundamentalist Christians and Moslems prefer that view, which refutes the notion that their putative designer is an all-loving, designer god, and makes it look like a malevolent, pestilential, misanthropic monster who hates its creation, rather than admit that the natural world is the inevitable result of the operation of basic laws of nature. But, as we so often observe in online 'debates' with fundamentalists, they will often prefer to denigrate their god and reduce themselves and their religion to absurdity than admit they are wrong.








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