#18,041
A little over 17 years ago in this blog - in Cats and Dogs and Flies, Oh My! - we looked at a 2006 study (see Detection and isolation of highly pathogenic H5N1 avian influenza A viruses from blow flies collected in the vicinity of an infected poultry farm in Kyoto, Japan, 2004 by Kyoko Sawabe et al.) that found that at least 2 types of flies could carry the H5N1 virus.
While flies weren't believed infected with the virus, they could ingest (and subsequently regurgitate or defecate) infected material, or potentially spread it mechanically by their feet or body, thereby spreading the disease.
The authors wrote:
The H5 influenza A virus genes were detected from the intestinal organs, crop, and gut of the two blow fly species, Calliphora nigribarbis and Aldrichina grahami, by reverse transcription-polymerase chain reaction for the matrix protein (M) and hemagglutinin (HA) genes. The HA gene encoding multiple basic amino acids at the HA cleavage site indicated that this virus is a highly pathogenic strain. . . . . Our results suggest it is possible that blow flies could become a mechanical transmitter of H5N1 influenza virus.
Four years later Dr. Sawabe and his team would publish (Blow Flies Were One of the Possible Candidates for Transmission of Highly Pathogenic H5N1 Avian Influenza Virus during the 2004 Outbreaks in Japan) where they conclude:
We have suggested here that blow flies are likely candidates for mechanical transmission of HPAI because of their ecological and physiological characteristics as reviewed here. In fact, blow flies have already been recognized as important vectors for mechanical transmission of several serious infectious diseases, that is, poxvirus [28], rabbit hemorrhagic disease [29], and paratuberculosis [30]. Recently, it has been reported that the H5N1 viral gene was detected in house flies [31] and engorged mosquitoes [32].
Last December, we looked at a brief synopsis of an upcoming study (see Kyushu University: The Return Of The Fly), which revisited this topic; testing blowflies for HPAI at the national wildlife reserve in Izumi City, Kagoshima Prefecture, which is the overwintering home for thousands of endangered Hooded Cranes.
`Until now, countermeasures have been taken based on the assumption that small animals and people will bring the virus. There was no improvement, and when we suspected it was a fly, a virus was detected.
We will conduct a more detailed investigation, take measures to prevent fly intrusion, and verify their effectiveness."
Given that American dairy farmers are now having to worry about HPAI biosecurity, and flies tend to be abundant around both cows and poultry, this research is certainly timely. We now have the full, English language version, which was published today in Science Reports.
I've only posted some excerpts, so follow the link to read it in its entirety.
Article
Open access
Published: 04 May 2024
Blowflies are potential vector for avian influenza virus at enzootic area in Japan
Ryosuke Fujita, Takuji Tachi, Masato Hino, Kosuke Nagata, Masahiro Saiki, Mizue Inumaru, Yukiko Higa, Kentaro Itokawa, Nozomi Uemura, Ryo Matsumura, Izumi Kai, Kyoko Sawabe, Mutsuo Kobayashi, Haruhiko Isawa, Takahiro Kusakabe, Kazunori Matsuo & Shinji Kasai
Scientific Reports volume 14, Article number: 10285 (2024) Cite this article
Abstract
High pathogenicity avian influenza (HPAI) poses a significant threat to both domestic and wild birds globally. The avian influenza virus, known for environmental contamination and subsequent oral infection in birds, necessitates careful consideration of alternative introduction routes during HPAI outbreaks.
This study focuses on blowflies (genus Calliphora), in particular Calliphora nigribarbis, attracted to decaying animals and feces, which migrate to lowland areas of Japan from northern or mountainous regions in early winter, coinciding with HPAI season. Our investigation aims to delineate the role of blowflies as HPAI vectors by conducting a virus prevalence survey in a wild bird HPAI-enzootic area.
In December 2022, 648 Calliphora nigribarbis were collected. Influenza virus RT-PCR testing identified 14 virus-positive samples (2.2% prevalence), with the highest occurrence observed near the crane colony (14.9%). Subtyping revealed the presence of H5N1 and HxN1 in some samples. Subsequent collections in December 2023 identified one HPAI virus-positive specimen from 608 collected flies in total, underscoring the potential involvement of blowflies in HPAI transmission.
Our observations suggest C. nigribarbis may acquire the HPAI virus from deceased wild birds directly or from fecal materials from infected birds, highlighting the need to add blowflies as a target of HPAI vector control.
(SNIP)
Blowflies represent a potential vector of HPAI, particularly in enzootic regions. The effectiveness of virus detection from flies relies heavily on the prevalence of infected and deceased wild birds. C. nigribarbis is widespread in human-populated areas across Japan, including semi-rural regions with poultry farms.
Like other insects, C. nigribarbis intermittently disperses its feces, leading to environmental contamination. In this study, we focused on C. nigribarbis because it was the dominant blowfly species in our study field and the season, but we could not exclude the contribution of other necrophagous blowflies in HPAI propagation, especially in geographical areas.
Although the extent of blowfly intrusion into poultry houses and their role as infection sources has not been extensively studied, it is important to pay equal attention not only to the intrusion of small animals or birds but also to the entry of flies into poultry houses15. Unfortunately, due to the lack of comparable data on virus prevalence in each vector and their invasion rates into poultry farms, we could not determine which vector poses a higher risk for HPAI transmission on poultry farms.
Unlike house flies, which often originate within poultry houses and are visibly active, C. nigribarbis does not exhibit such behavior. While they may appear elusive, they can be readily captured in winter using baits or traps. Considering the possible involvement of blowflies in HPAI transmission, it would be advisable to implement fly control measures in poultry settings, such as utilizing fine mesh nets, fly traps, or insecticides.
(Continue . . .)
