Insects as vectors of blackhead disease

Are darkling beetle’s carriers of Histomonas?
calendar icon 5 April 2023
clock icon 2 minute read

Histomonas meleagridis is commonly found in broiler breeder pullet farms, where it can cause disease characterized by typical lesions in ceca and liver, known as histomoniasis or blackhead disease. Histomonas can use the eggs of the cecal worm Heterakis gallinarum as vectors and reservoirs. Moreover, cecal worm eggs are not only very resistant in the environment but can also be carried by arthropods.

However, little is known about which arthropod species are the most robust vectors. A study was done to define relevant arthropod vectors of H. meleagridis and H. gallinarum in broiler breeder pullet flocks. The research was done by Maria Tereza Terra-Long and colleagues at Auburn University and Wayne-Sanderson Farms and presented at the 2023 International Poultry Scientific Forum.

Over a period of one year, four broiler breeder pullet farms were sampled every four months. On each farm, three types of traps were set inside and outside two houses and remained for a period of one week. Trapped insect specimens were morphologically identified at order level. Fifty-one hundred ninety-nine individual insects from 11 orders were counted and attributed to 319 different types.

Traps kept outside had a higher abundance of arthropods with 3,459 individuals from 10 orders than inside traps with 1,740 individuals from eight orders. Alpha diversity of the insect populations was significantly higher in traps kept outside and beta diversity analysis showed that individuals were clustered together based on their location and seasons.

Diptera was the most common order and darkling species the most common type with 1806 specimens. Almost all (99%) of the darkling beetles were found inside the houses and only one was found on a hanging glue trap, which suggests that darkling beetles are unlikely to carry diseases from house to house or even farm to farm.

There was an outbreak of histomoniasis at one farm during the second collection. PCR analysis showed that 50% of the darkling beetles were positive for Histomonas DNA four months after the outbreak. H. gallinarum DNA was sporadically detected in beetles on all farms.

In addition, 170 other insects were selected for DNA extraction based on their detection at several time points inside as well as outside the houses. Out of those, four samples were positive for Histomonas and one for Heterakis. Three of these insects were also collected four months after the blackhead outbreak.

The role of these insects as potential vectors for Histomonas should be further investigated, noted the researchers.

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