# Contributions to Knowledge of the Dictyocaulus Infection of the Red Deer

## TL;DR

This study identifies new Dictyocaulus worm species infecting red deer in Spain and highlights genetic diversity and potential species mixing.

## Contribution

First-time identification of D. cervi and D. eckerti in the region and evidence of genetic introgression between Dictyocaulus species.

## Key findings

- Molecular analysis confirmed three genetic groups of Dictyocaulus in red deer.
- D. cervi and D. eckerti were newly identified in the study area.
- Genetic introgression between D. cervi and D. eckerti was suggested.

## Abstract

The genus Dictyocaulus comprises eighteen species of worms, but only four of these infect red deer. Infection results in damage to the respiratory tract, ranging from emphysema or edema to microscopic inflammatory and hemorrhagic lesions. Larvated eggs are expelled externally through coughing or feces, leading to the release of L1 into the environment. Worms from positive lungs collected in Extremadura (Spain) were examined using morphological identification, along with analyses of anatomopathological lesions and molecular barcode identification. The presence of three genetic groups was confirmed through significant subdivision using the ɸST measure, but D. cervi and D. viviparus exhibited their respective matrilineal ancestry, while D. eckerti and D. cervi showed matrilineal sharing. Consequently, the need to evaluate introgression between these two species was highlighted. D. viviparus was discarded despite having been previously reported in the same Spanish location using morphological methods, and D. cervi and D. eckerti were identified for the first time in the geographical area explored.

Dictyocaulosis is a parasitic disease that affects ungulate species, including red deer (Cervus elaphus). The genus Dictyocaulus comprises eighteen species, but only four have been reported to infect red deer. The disease is characterized by respiratory tract infection, particularly in the lungs, bronchi, and bronchioles, leading to inflammatory and hemorrhagic microscopic lesions, as well as emphysema and edema. The biological cycle involves a female ovipositing larvated eggs in the bronchi and trachea, which are expelled to the exterior through coughing or feces, releasing L1 into the environment. In this study, 106 adult red deer were collected from seven locations in Extremadura (Spain). Eight positive lungs were initially assessed by morphological identification, revealing a mean intensity of 13.3 adult worms per infected lung, with a global decrease to an average of 1.8 adult worms per sampled lung. The presence of adult worms in the upper and middle respiratory tract was confirmed through anatomopathological analysis. Molecular identification was performed by sequencing the COI gene. The results indicated the presence of three genetic groups, supported by significant subdivision using the ɸST measure. D. cervi and D. viviparus exhibited their respective matrilineal ancestry, while D. eckerti and D. cervi demonstrated matrilineal sharing. Consequently, the possibility of introgression between these two species was suggested. Although D. viviparus had previously been identified in the same Spanish region based on morphological characteristics, D. cervi and D. eckerti were reported for the first time in the explored geographic area.