Do larvae of trichobilharzia szidati and echinostoma revolutum generate behavioral fever in lymnaea stagnalis individuals?

Abstract

The objective of this study was to determine whether individuals of Lymnaea stagnalis naturally parasitized with Trichobilharzia szidati and Echinostoma revolutum can generate the behavioral fever against larvae of those parasites. Thermal preferences of each snail were examined in an oblong thermal gradient during 48 h observation. Uninfected animals under study chose higher temperatures than those releasing cercariae of parasites. Infected snails kept in constant temperature lived shorter than uninfected ones. At high temperature, they released more cercariae per day than at low temperature. Temperature had a great influence on the longevity of emerged cercariae. The thermal behavior of infected snails is not a symptom of behavioral fever but probably can play a therapeutic role in the host.

Avian Schistosomes and Outbreaks of Cercarial Dermatitis

“…As an example, 90% of L. stagnalis snails infected experimentally with a single miracidium of T. ocellata (North American isolate) were alive at 28 weeks of age (three infected snails were alive for 19 months), whereas all uninfected snails were dead (168). In contrast, L. stagnalis or Planorbarius corneus snails naturally infected with T. szidati or Bilharziella polonica, respectively, lived a shorter time, on average, than the corresponding uninfected individuals (169,170).…”

“…In this regard, temperature strongly affects cercarial survival. For example, the half-life of T. szidati was 16 h at 16°C but only 7.8 h at 25°C (169), and the life span of Trichobilharzia arcuata was 72 h at 4°C but only 48 h at 26°C (277). Infected snails change their thermal microhabitat selection, e.g., Lymnaea stagnalis infected with T. szidati prefers a colder water temperature than that preferred by uninfected snails (19.97°C versus 25°C).…”

“…Infected snails change their thermal microhabitat selection, e.g., Lymnaea stagnalis infected with T. szidati prefers a colder water temperature than that preferred by uninfected snails (19.97°C versus 25°C). This may be an adaptation for either the snail or the schistosome, because at these temperatures larval development is slower and the rate of cercarial emission is lower, leading to less tissue damage in the snail (169,170).…”

“…Most cases of cercarial dermatitis correlate with high air and water temperatures during the summer months, when schistosome development in snails is amplified and emission rates of cercariae are stimulated by sunlight (4,11,279,280,304,305,309,314). Production can reach several thousands of cercariae/snail/day (169,300,315), and these emission rates may even counterbalance the loss of cercarial capability to survive and infect hosts at high temperatures (see above). Irrespective of the season, outbreaks of cercarial dermatitis have been reported in geothermally heated lakes and ponds in Iceland (71).…”

“…Thus, Trichobilharzia and some other genera infecting aquatic birds leave the snail host during the light period of the day, mainly in the morning hours (2,4,280,305). Increased illumination, temperature, and snail locomotory activity trigger cercarial emergence (169,211,316,317). Patterns of cercarial emergence can be changed almost immediately by reversing the dark-light regimen, suggesting that light has a decisive influence on the direction of the process (317,318).…”