Anomotaenia brevis


Anomotaenia brevis is a tapeworm which has been found to be one of many parasite species able to manipulate their host's behavior. Host manipulation is commonly observed in parasites with complex life cycles reliant on multiple hosts for development. While the definitive host for A. brevis is the woodpecker, their intermediate host is the Temnothorax ''nylanderi, a species of ant located in the oak forests of western Europe. The tapeworm alters the appearance and behavior of the T. nylanderi ant in order to ensure transmission to the woodpecker, where it can complete its life cycle.
The tapeworm affects the behavior, life history, and morphology of the T. nylanderi ant, as well as indirectly affects its uninfected nest-mates. The ant larva is infected after feeding on bird faeces contaminated with A. brevis'' eggs. The tapeworm penetrates the ant's gut wall and develops into a cysticercoid within the haemocoel. As the parasitic tapeworm larvae develops in the ant's body, the ant begins to change. They smell different from and are smaller than their nest-mates, their cuticles turn yellow instead of the usual brown color, and they tend to stay sitting in the nest. They also have a higher survival rate compared to their uninfected nest-mates, which allows the parasite to have a higher chance at reaching the definitive host.
Morphology
Adult Anomotaenia brevis are small cestodes typically measuring 5–15 cm in total length. Like other cyclophyllideans, the worm possesses:
1. Scolex with hooks used for attachment to the intestinal mucosa
2. Series of proglottids that mature toward the posterior end
3. Reproductive system contained in each proglottid, allowing high egg production
Eggs contain an oncosphere larva and are shed in the feces of infected birds. Their morphology is similar to other members of Dilepididae, with thick-walled capsules adapted for survival in the external environment.
Life Cycle
The life cycle of A. brevis is indirect, requiring at least one intermediate host. In short eggs passed in bird feces contaminate the environment. There are two different types of host that this parasite moves through and that is the definitive host which is known as the Pied flycatcher and the intermendiate hosts which are suspected to be beetles and other small incescts consumed by flycatchers. Research on A. brevis in Scandinavian bird populations indicates variable prevalence between years, with infection intensity influenced by food availability and insect population changes.
  • Intermediate host ingestion:
studies suggest arthropods such as small insects or myriapods act as intermediate hosts. The oncosphere penetrates the gut and develops into a cysticercoid larva.
  • Definitive host infection:
the pied flycatcher becomes infected by consuming the infected arthropod during foraging.
  • Maturation:
in the intestine of the bird, the cysticercoid develops into an adult tapeworm and begins producing eggs.
This life cycle structure is consistent with most Dilepididae species that parasitize passerine birds.
Effects on the Host
In pied flycatchers, infections with A. brevis have been associated with:
  • Reduced body condition
  • Altered immune responses
  • Decreased reproductive output in heavily parasitized birds
A study by Tomás et al. found that experimentally dewormed females produced larger clutches compared to untreated controls, suggesting A. brevis imposes measurable fitness costs.
Ecology
The pied flycatcher is migratory, A. brevis distribution spans Europe, particularly Scandinavia, where most research has been conducted. Environmental conditions that affect insect abundance indirectly alter parasite transmission rates.
Research has examined whether cestode infections influence host testosterone or behavior. While results are mixed, some studies suggest potential trade-offs between immune activation and reproductive investment in infected males.
Diagnosis in wild bird populations is generally performed through: Fecal egg counts, Post-mortem intestinal examination, and Molecular identification of eggs or proglottids. Cestode eggs are morphologically similar across species, molecular markers improve identification accuracy.
Treatment
In experimental studies, birds are often treated with praziquantel, which effectively clears cestode infections and allows researchers to study the physiological effects of parasite removal.