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article imageInsight into parasite transmission from tsetse fly bites

By Tim Sandle     Jul 28, 2016 in Science
Tsetse flies can infect people, and other animals, with parasites via their bite. Little has been known about the number of parasites needed for an infection to occur. This has changed with a new study.
The study has looked at Trypanosome parasites, which cause sleeping sickness. The infection is common to parts of Africa. Sleeping sickness refers to a range of different parasitic diseases. The recent study has looked into African trypanosomiasis. This is caused by a single-celled animal (protozoa) called Trypanosoma brucei. The only medication that can treat all forms of the disease is Melarsoprol (due to the parasite developing resistance to other drugs.) However, the chemical carries a risk of toxicity.
The research has revealed that very few parasites are needed to colonize the host. The study has also show that the multiplication of parasites at the bite site creates a reservoir. Here the parasites can be transferred to a new host via subsequent tsetse fly bites.
The life-cycle of the parasites is complex, involving several stages in hosts. Studies have been hampered by the need to inject animal models with the parasites. This type of research is regarded as limited because it does not exactly replicate what happens with a fly bite. Being able to replicate transmission by flies involves the natural inoculation of what are called “metacyclic trypanosomes.”
Transmission of the parasite by flu bites has recently been studied using mice, by researchers from the Institute of Tropical Medicine in Antwerp. With this the parasites were fluorescently tagged. This has allowed for a clearer visualization of trypanosomes.
With this it was found that metacyclic trypanosomes are highly infectious, seemingly more infectious than those artificially introduced in other studies. The number of parasites required to infect a mouse are found to be as low as seven (compared with upwards of 200 in ‘test tube’ studies.)
The study further found that the parasites congregate around the site of the original bite for at least seven days. This allows some of the parasites to be picked up by another fly (should it bite the infected host), enabling transfer to a new host. Around this site inflammation was notable and the region was warmer than with other parts of the mouse body.
The research has been published in the journal PLOS Pathogens. The research paper is titled “The Dermis as a Delivery Site of Trypanosoma brucei for Tsetse Flies.”
More about Parasites, tsetse fly, Sleeping sickness, Africa
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