Haematobium irritans and Haematobium titillans as potential vectors of Parabronema skrjabini in camels (Camelus bactrianus) in Inner Mongolia, China.

Parabronema skrjabini is one of the most harmful nematodes to camels and is responsible for economic losses in animal husbandry industry. There is an urgent need for in-depth studies of potential vectors of the nematode due to its scant regarding information. As previous studies indicated that flies may be the vectors of P. skrjabini, we captured flies in the main camel-producing areas of Inner Mongolia. After autopsy of the specimens of two species of horn flies, we observed the morphology of the suspected nematode larvae found in them. Internal transcribed spacer ribosomal-DNA gene sequences were considered the best candidate to confirm the species of the larvae found. Our results showed that the homology compared with P. skrjabini was 99.5% in GenBank. Subsequently, we preliminarily identified two species of horn flies through morphological observation and then sequenced the mitochondrial-DNA-gene cytochrome oxidase subunit I obtained from two species of horn flies, with 100 and 99.2% similarity to sequences deposited in GenBank, respectively. Thus, we identified Haematobia titillans and Haematobia irritans and provided evidence for their potential role as vectors of parabronemosis. Our study provides reference for future research on the life history of the nematode and the vectors of parabronemosis.

Parabronema skrjabini (Nematoda: Habronematidae) infection and development in the intermediate host-Haematobia irritans (Linnaeus, 1758) in Inner Mongolia, China.

Parabronemosis is a disease that severely threatens camel health, causing huge economic losses to industries involved in camel husbandry. Previous studies have reported that horn flies (Haematobia irritans) act as intermediate hosts of Parabronema skrjabini; however, the infection and developmental processes of P. skrjabini in horn flies remain unclear. In the present study, the infection rates of P. skrjabini were determined in morphologically and molecularly identified horn flies collected from Bactrian camels (Camelus bactrianus) producing regions in Inner Mongolia, China that have high P. skrjabini infection rates. The horn flies were dissected to obtain the nematode larvae at various instar stages. The P. skrjabini found in the different instar stages of horn fly instars were counted and identified to assess the infection and developmental status. Nematode larvae at different developmental stages were obtained from the horn fly instars for further molecular analysis. Sequencing results confirmed that the nematode larvae were P. skrjabini. Furthermore, we found that the mean growth rate of the nematode larva increased as the horn fly instars develops. The results suggested that P. skrjabini infected the horn flies at the larval instar stage, and that the nematode larvae developed simultaneously with the horn fly instars stages. Our findings provide useful information into the elucidation of P. skrjabini infection and life history by studying horn fly development.