Friday, 17 June 2016

The early bird catches the parasite

Frigate Bird by ryanlerch
by Luisa Harper
Are insects the key to saving birds?
Red-banded Partridge chick.
Dr Carly Benefer from the University of Plymouth is researching nematode parasites that infect a large variety of birds, though they have a huge impact on game and poultry in particular. The parasite causes gape, a disease that obstructs the trachea of the birds and causes them to gasp for breath. If it’s not treated with ivermectin (a drug) the parasite causes death, and is particularly deadly in chicks.
The drugs used to treat gape are not pleasant and are hard to implement in wild populations. Problems become more apparent when parents feed their chicks soil invertebrates, such as slugs and earthworms, and it has been suggested that gape is more prevalent in areas where there is higher precipitation. However, most of the current knowledge is about the bird epidemiology rather than the parasite.

Gapeworm (Syngamus trachea) is a parasitic nematode worm that infects the trachea of birds, and the ‘gape’ condition is caused when the worms obstruct the airway. It is known that the parasite spends most of its life cycle encysted in soil invertebrates, which are paratenic hosts (the nematode does not develop while in this host). Birds cough out spores that fall into the soil, invertebrates pick the spores up when moving around and these spores then remain here until picked up by the birds, where they spend the remainder of their life cycle, finally developing into adults which migrate to the trachea. What we don’t know is how the ecology of these infected invertebrates affects the transmission to the birds.

Gape worm in trachea of a bird.
Carly often uses molecular techniques to answer questions on the ecology of important invertebrate taxa that are otherwise difficult because the methods traditionally available require a high level of expertise, are difficult, time consuming and/or costly. Her work particularly focuses on species identification and interactions.

Here she aims to look at which soil invertebrates harbour the gapeworm parasite, and how invertebrate distribution affects the transmission to birds and the incidences of the disease. This is particularly important for game birds which are kept in pens in which there are often congregations of invertebrates around feeding areas. So far the work carried out has only been observational, partly because it is very difficult and time-consuming to dissect insects to discover the parasite.

A new method is currently being developed using qPCR, a molecular technique which can detect very small quantities of parasite DNA within invertebrates. This involves extracting DNA from the invertebrate and using specific primers, developed from DNA sequences previously obtained from the gapeworm parasite, to detect the parasite (but not the host) DNA using PCR. Initially the aim is to develop this method to detect small quantities of gapeworm DNA in mixtures of host and parasite DNA, but in the longer term it is hoped this can be used to assess which invertebrates are most likely to have the parasite and to focus on these in future larger projects.

This issue is of conservation importance as it affects a number of birds of conservation concern, such as the red partridge. It is also commercially important as it affects game birds and poultry, as well as other wild birds, which potentially interact with those that are commercially reared. Having a method which allows a quick and easy assessment of which invertebrates are involved in disease transmission should help focus future work on methods to prevent them passing on the parasite.

Syngamus trachea (gapeworm) in the trachea of a ringnecked pheasant.
By Milton Friend at the Geological Survey National Wildlife
Health Center [Public domain], via Wikimedia Commons

This article was originally submitted as a science communication assignment, for part of the BSc (Hons) Conservation Biology degree. It has been edited before posting here.

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