Identification of the Pathogen Dorcadia ioffi Smit and Evaluation of the Effect of Different Drugs

TL;DR

This study identifies a flea species affecting sheep in Xinjiang and finds that cypermethrin and dichlorvos are highly effective against it.

Contribution

The study identifies Dorcadia ioffi Smit as the prevalent Vermipsyllid species and screens effective anthelmintic drugs for it.

Findings

Dorcadia ioffi Smit was identified as the prevalent Vermipsyllid species in Xinjiang's Altai region.

Cypermethrin and dichlorvos pour-on treatments achieved 100% flea population reduction and cure rates.

Avermectin, ivermectin, and moxidectin showed poor efficacy against D. ioffi.

Abstract

Vermipsyllid parasitize the surface of livestock, feeding on blood and transmitting diseases, which causes severe economic losses to the livestock industry. An outbreak of sheep Vermipsyllid fleas occurred in the mountain pastures of the Altai region, Xinjiang, with clinical treatment revealing significant resistance of this flea species to multiple commonly used anthelmintic drugs. This study identified the local Vermipsyllid species through morphological observation and molecular biological analysis and compared the deworming effects of different drugs via pharmacodynamic experiments. The results showed that the prevalent local species was Dorcadia ioffi Smit (D. ioffi); cypermethrin and dichlorvos exhibited high insecticide activity. This study clarified the species of sheep Vermipsyllid in the region, screened highly effective anthelmintic drugs, and provided a scientific basis for the diagnosis of such parasitic diseases, selection of anthelmintic drugs in pastures, and reduction in drug resistance risks and prevention and control.

Vermipsyllid parasitize the body surface of sheep, feeding on blood and transmitting diseases, causing severe economic losses to the livestock industry. An outbreak of sheep Vermipsyllid fleas in the mountain pastures of Xinjiang’s Altai region showed that several commonly used commercial anthelmintic drugs had poor therapeutic effects on the prevalent flea species. This study first conducted species identification of Vermipsyllid through morphological analysis of 200 female and 40 male specimens collected from the Altai region, followed by molecular biological identification of 6 randomly selected fleas (3 females and 3 males). Finally, pharmacodynamic experiments were performed to screen for highly effective anthelmintic drugs. Ninety Altai multiparous ewes infected with Vermipsyllid were divided into six groups (fifteen sheep per group): an untreated control group (Ctr), avermectin injection group (Group I), ivermectin injection group (Group II), moxidectin pour-on group (Group III), cypermethrin pour-on group (Group IV), and dichlorvos pour-on group (Group V), with a 14-day trial period. On Day 0, each group received a single treatment according to drug instructions and specified dosages. The number of fleas, flea population reduction rates, and cure rates were measured on Day 0, Day 3, Day 7, and Day 14 to screen for effective anthelmintic drugs. Results showed that unfed female and male fleas were grayish-brown. Engorged females reached 14.15 mm in size, appearing pale white or yellow, with their sterna maintaining the original size and shape despite abdominal distension. Female fleas had 20–21 segments on the labium, while males had 16–19 segments. The hind tibiae featured four notches, and each side of the tergite had 13 ± 1 cup-like indentations. Molecular biological identification indicated that the identified fleas belonged to D. ioffi (Vermipsyllidae, Dorcadia Ioff), showing 99.13% sequence similarity with D. ioffi from Xinjiang, China. In pharmacodynamic experiments, the number of D. ioffi in Groups IV and V decreased to zero on both Day 7 and Day 14, which was extremely significantly lower than other groups (p < 0.01). The flea population reduction rates in Groups IV and V reached 100% on both days. By Day 14, the cure rates of Groups I, II, and III were 0%, while those of Groups IV and V were 100%. Avermectin injection, ivermectin injection, and moxidectin pour-on showed poor anthelmintic effects, whereas cypermethrin and dichlorvos pour-on exhibited high anthelmintic activity against this flea species.

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