Abstract
Background:
Filariasis is a parasitic disease caused by filarial nematodes. The life cycle involves vertebrates host and hematophagous arthropods. Filarial nematodes are viviparous, and their larvae (microfilaria) are produced into the blood circulation. Microfilariae are widely studied in humans and small animals, but are rarely found in domestic chickens.

Aim:
We aimed to study the prevalence, morphology, and molecular characteristics of microfilariae in village chickens raised in Thailand.

Methods:
Sixty thin blood smears were prepared for parasite detection and morphotype observation. A total of 60 genomic DNA were used for nested-PCR amplification of the cytochrome c oxidase 1 (COX1) gene. The amplicons were then sequenced and used for Bayesian phylogenetic analysis.

Results:
The prevalence of microfilariae in domestic chickens raised in Northeastern Thailand was 36.66%. Three morphotypes of microfilariae were identified. Eleven out of 22 samples exhibited a single morphotype infection. Of these, only two samples were identified as single-strain infections. One sequence isolated from unsheathed microfilaria was phylogenetically grouped with other Eufilaria spp., with 9.95%–10.57 % genetic divergence. Thus, this unsheathed microfilaria was identified as Eufilaria sp. (GenBank accession no: PQ564658).

Conclusion:
The prevalence of microfilariae in Thai chickens was high. This report highlighted that the sequence of the COX1 gene and morphological characteristics confirmed Eufilaria infection. This study sheds light on the identification and diagnosis of microfilaria and filarial nematode infection in chickens. However, the sensitivity of the available nested-PCR was limited. Further design of primers using our reported sequences may resolve this problem. Thus, the data from this study can be considered as baseline information for further studies.

Key words: Eufilaria, COX1, Morphotypes, Onchocercidae, Thailand