TDK conference 2019

The larvae of protostrongylid worms, which cause nodular lungworm disease in rabbits, reach their third larval stage in terrestrial snails. Only this stage of larvae is able to infect the rabbit. In Hungary, usually the common heath snail, (Xerolenta obvia), carries protostrongylid larvae, including larvae of rabbit lungworms. It is relatively easy to understand and experimentally verify the way how the snail becomes infected by the larvae getting from the rabbit faeces, but no one has yet proved the way how infectious larvae enter the rabbit.

To date, there is no consensus among scientists whether the predominantly herbivorous rabbit eats the snails or the larvae crawl out of the snail onto the grass and thus enter the animal's mouth. This issue is of practical importance because other animals that do not regularly eat snails, such as dogs and cats, and humans also can become infected with larvae that develop in land snails. Therefore, we wanted to obtain data on the relationship between larvae and snails. We examined whether there is a correlation between the development of snails and their larval content in one of the meadows of the Tétényi Plateau and whether the frequency of larvae shows any seasonality.

From spring to late autumn, we collected a total of 1701 X. obvia snails at fortnightly intervals and determined the number of worms in each specimen. The development of the snails was estimated on the basis of their shell size. Simultaneously with the collection of the snails, the larvae content of the rabbit faeces collected on the ground was examined, and we also collected approximately 200-200 litres of grass samples twice in those places where Xerolenta snails crawled on the plants. The degree of larval development was also determined by microscopic examination.

The size of the snails did not significantly affect the number of larvae settled in the snail, but since most larvae were collected in the summer months and in early autumn, the frequency of infection suggests seasonality. The rabbit faeces collected at the same time as the snails also contained larvae mainly during the same period, but not at all during the winter months. Third-stage larvae that could infect rabbits could not be isolated from herbaceous plants in either the summer or winter months.

We presume that during the summer activity of snails, more and more larvae intrude into them, but the larvae can penetrate snails of all ages. Therefore, by the time the snails are crawling in large numbers on the leaves of grass, both smaller and larger snails will be infected. Since there are no snails on the soil surface in winter, the peaking in the number of larvae should be related to the way the rabbits are infected, which seems to be a seasonal phenomenon.