Pilot study on the efficacy of paromomycin as a histomonostatic feed additive in turkey poults experimentally infected withHistomonas meleagridis

Advances in riboswitch-based biosensor as food samples detection tool

Food safety has always been a hot issue of social concern, and biosensing has been widely used in the field of food safety detection. Compared with traditional aptamer-based biosensors, aptamer-based riboswitch biosensing represents higher precision and programmability. A riboswitch is an elegant example of controlling gene expression, where the target is coupled to the aptamer domain, resulting in a conformational change in the downstream expression domain and determining the signal output. Riboswitch-based biosensing can be extensively applied to the portable real-time detection of food samples. The numerous key features of riboswitch-based biosensing emphasize their sustainability, renewable, and testing, which promises to transform engineering applications in the field of food safety. This review covers recent developments in riboswitch-based biosensors. The brief history, definition, and modular design (regulatory mode, reporter, and expression platform) of riboswitch-based biosensors are explained for better insight into the design and construction. We summarize recent advances in various riboswitch-based biosensors involving theophylline, malachite green, tetracycline, neomycin, fluoride, thrombin, naringenin, ciprofloxacin, and paromomycin, aiming to provide general guidance for the design of riboswitch-based biosensors. Finally, the challenges and prospects are also summarized as a way forward stratagem and signs of progress.

Retrospective Investigations of Recurring Histomonosis on a Turkey Farm

The ban of effective feed additives and therapeutics in the European Union and in other parts of the world led to a dramatic increase of histomonosis in turkeys. Despite the impact of the disease on the health and welfare of poultry, many questions remain open regarding the epidemiology of the pathogen. In this study, we retrospectively monitored a farm with recurring cases of histomonosis to identify possible routes of pathogen introduction and predisposing factors that may influence the disease development. We included 32 consecutive turkey flocks, which were fattened between 2007 and 2021 on the same farm under the same management and housing conditions. During this period, Histomonas meleagridis was detected in eight flocks of toms and four flocks of hens with a high variability in disease development. Outbreaks in toms led to significantly (P ≤ 0.05) higher mortality rates (5.3%-98.3%) than in hens (2.6%-6.1%). Most of the outbreaks (9/12) were diagnosed between June and September with a peak in August, suggesting a possible impact of higher temperatures either on the host or on the pathogen and pathogen-transmitting vectors. Further investigation is necessary to determine why hens might cope better with histomonosis than toms. Continuous flock and hygiene management is important to prevent an introduction of the causative pathogen and to control potential vectors.

Histomonosis in Poultry: A Comprehensive Review

Histomonas meleagridis, the etiological agent of histomonosis, is a poultry parasite primarily detrimental to turkeys. Characteristic lesions occur in the liver and ceca, with mortalities in turkey flocks often reaching 80-100%. Chickens and other gallinaceous birds can be susceptible but the disease was primarily considered sub-clinical until recent years. Treating and preventing H. meleagridis infection have become more difficult since 2015, when nitarsone was voluntarily removed from the market, leaving the poultry industry with no approved prophylactics, therapeutics, or vaccines to combat histomonosis. Phytogenic compounds evaluated for chemoprophylaxis of histomonosis have varied results with in vitro and in vivo experiments. Some recent research successes are encouraging for the pursuit of antihistomonal compounds derived from plants. Turkeys and chickens exhibit a level of resistance to re-infection when recovered from H. meleagridis infection, but no commercial vaccines are yet available, despite experimental successes. Safety and stability of live-attenuated isolates have been demonstrated; furthermore, highly efficacious protection has been conferred in experimental settings with administration of these isolates without harming performance. Taken together, these research advancements are encouraging for vaccine development, but further investigation is necessary to evaluate proper administration age, dose, and route. A summary of the published research is provided in this review.

Maximum levels of cross-contamination for 24 antimicrobial active substances in non-target feed. Part 2: Aminoglycosides/aminocyclitols: apramycin, paromomycin, neomycin and spectinomycin

The specific concentrations of apramycin, paromomycin, neomycin and spectinomycin in non-target feed for food-producing animals, below which there would not be an effect on the emergence of, and/or selection for, resistance in bacteria relevant for human and animal health, as well as the specific antimicrobial concentrations in feed which have an effect in terms of growth promotion/increased yield, were assessed by EFSA in collaboration with EMA. Details of the methodology used for this assessment, associated data gaps and uncertainties, are presented in a separate document. To address antimicrobial resistance, the Feed Antimicrobial Resistance Selection Concentration (FARSC) model developed specifically for the assessment was applied. However, due to the lack of data on the parameters required to calculate the FARSC for these antimicrobials, it was not possible to conclude the assessment until further experimental data become available. To address growth promotion, data from scientific publications obtained from an extensive literature review were used. Levels in feed that showed to have an effect on growth promotion/increased yield were reported for apramycin and neomycin, whilst for paromomycin and spectinomycin, no suitable data for the assessment were available. It was recommended to carry out studies to generate the data that are required to fill the gaps which prevented the calculation of the FARSC for these four antimicrobials.

Critical Review: Future Control of Blackhead Disease (Histomoniasis) in Poultry

Blackhead disease (histomoniasis) currently has no efficacious drug approved for use in poultry in the United States. Both chickens and turkeys can get the disease, but mortality is most often associated with turkeys. The lack of any approved therapies for blackhead is of concern, especially in the case of valuable turkey breeder candidate flocks. Due to the availability of efficacious drugs for many years, research focused on blackhead was minimal. However, without any drugs or reliable additives, blackhead will continue to be an issue in turkeys and broiler breeder chickens. The American Association of Avian Pathologists annual meeting in San Antonio, Texas, August 6-9, 2016, held a mini-symposium on blackhead. The mini-symposium included university researchers and industry veterinarians discussing blackhead in the United States and Europe including insights on the disease pathogenesis and epidemiology, as well as an update on the current state of blackhead in the United States since the removal of nitarsone from the market in January 2016. This review summarizes the information presented at the mini-symposium and discusses current control measures in an era without efficacious drugs.

Quantification of parasite shedding and horizontal transmission parameters in Histomonas meleagridis-infected turkeys determined by real-time quantitative PCR

To gain more insight into the within flock transmission of Histomonas meleagridis, the shedding of parasites was quantified by a newly developed real-time quantitative (q)PCR and the basic reproduction number (R0) and the mean number of secondary infections per infectious bird per day in a susceptible population (β) of H. meleagridis in the absence of heterakis were assessed. Forty turkeys were divided into two groups of 10 and 30 birds at 14 days of age. Birds of the first group were inoculated with 200,000 histomonads each, the second group served as a susceptible contact group. Cloacal swabs were taken at -1, 1, 4, 7, 9, 11, 14, 18 and 21 days post inoculation (p.i.) to assess the shedding of the parasite by the qPCR (detection limit 330 histomonads/ml droppings). The experiment ended at 28 days p.i. Mortality was 100% in the inoculated birds and started at day 12 p.i., while in the contacts, it was 83% and started at 16 days p.i. Shedding started 1 day after the inoculation in both groups. The mean shedding levels (and 95% CI) expressed as parasite equivalents per gram cloacal content on a log10 scale in the inoculated, contact birds that died and contact birds alive were 2.0 (1.6-2.4), 1.6 (1.4-1.9) and 1.2 (0.5-2.0), respectively. Birds that died shed histomonas more often and were infectious for 13.4 days; in contrast, those that recovered were infectious for 5.7 days. R0 was estimated to be 8.4 and β 0.70. Simulations made with the parameters obtained were in agreement with the experimental results, confirming their validity.

Histomonosis in poultry: previous and current strategies for prevention and therapy

Histomonosis is a parasitic disease of poultry with worldwide prevalence. The disease can cause morbidity and mortality in chicken and turkey flocks entailing severe economic losses. In the first half of the last century, there was a high demand to control histomonosis as the turkey industry was severely affected by the disease. Consequently, numerous chemical compounds were tested for their efficacy against Histomonas meleagridis with varying outcomes, that are summarized and specified in this review. At the same time, preliminary attempts to protect birds with cultured histomonads indicated the possibility of vaccination. Several years ago antihistomonal drugs were banned in countries with tight regulations on pharmaceuticals in order to comply with the demand of consumer protection. As a consequence, outbreaks of histomonosis in poultry flocks increased and the disease became endemic again. New approaches to prevent and treat histomonosis are, therefore, needed and recently performed studies focused on various areas to combat the disease, from alternative chemotherapeutic substances to plant-derived compounds until vaccination, altogether reviewed here. Considering existing regulations and the overall outcome of experimental studies, it can be concluded that vaccination is very promising, despite the fact that various challenges need to be addressed until the first ever developed vaccine based upon live flagellates in human or bird medicine can be marketed.

Histomonosis - an existing problem in chicken flocks in Poland

Histomonosis (histomoniasis, blackhead), beside coccidiosis, belongs to the most important parasitic protozoan diseases in poultry. So far Histomonas meleagridis infections with varied mortality rates have been mainly diagnosed in young turkeys. Recently an increasing number of cases have been reported in chicken flocks in Europe resulting in economic losses. It is thought that this situation is predominantly caused by a complete withdrawal of the effective antihistomonals in the EU. Authors listed the selected outbreaks of histomonosis in 10 chicken flocks originated from different farms of 4 regions in Poland: 8 broiler breeder flocks (at mean age of 33 weeks) and 2 commercial layers flocks (at mean age of 38 weeks). This study reported here naturally occurring case of H.meleagridis infection in commercial broiler breeder (BB) flock line ROSS 308 at the age of 16 weeks. We showed acute form of infection with characteristic necrotic foci in the liver, and ulcerative typhilitis. Beside the liver and caeca, the multiple histomonads, lymphoid tissue depletion and heavy destruction in the bursa of Fabricius were observed. Additionally, the absence of systemic diffuse histomonads and lack of Heterakis gallinarum, caecal worm eggs in faecal samples were noted. PCR technique enabled to detect the presence of H.meleagridis genetic material in the investigated tissue samples. Authors indicate that histomonosis can be considered as re-emerging infectious diseases in chicken flocks of intensive production system.

Histomonas meleagridis--new insights into an old pathogen

The protozoan flagellate Histomonas meleagridis is the etiological agent of histomonosis, first described in 1893. It is a fastidious disease in turkeys, with pathological lesions in the caeca and liver, sometimes with high mortality. In chickens the disease is less fatal and lesions are often confined to the caeca. The disease was well controlled by applying nitroimidazoles and nitrofurans for therapy or prophylaxis. Since their introduction into the market in the middle of the previous century, research nearly ceased as outbreaks of histomonosis occurred only very rarely. With the ban of these drugs in the last two decades in North America, the European Union and elsewhere, in combination with the changes in animal husbandry, the disease re-emerged. Consequently, research programs were set up in various places focusing on different features of the parasite and the disease. For the first time studies were performed to elucidate the molecular repertoire of the parasite. In addition, research has been started to investigate the parasite's interaction with its host. New diagnostic methods and tools were developed and tested with samples obtained from field outbreaks or experimental infections. Some of these studies aimed to clarify the introduction of the protozoan parasite into a flock and the transmission between birds. Finally, a strong focus was placed on research concentrated on the development of new treatment and prophylactic strategies, urgently needed to combat the disease. This review aims to summarize recent research activities and place them into context with older literature.

Antihistomonal effects of artemisinin and Artemisia annua extracts in vitro could not be confirmed by in vivo experiments in turkeys and chickens

Five different Artemisia annua-derived materials (i.e. dry leaves, pure artemisinin, and hexane, dichloromethane or methanol extracts of leaves) were screened for their in vitro activities against six clonal cultures of Histomonas meleagridis. Except for the methanol extract, all tested materials displayed in vitro activity against all tested protozoal clones. Neither the dry plant material, extracts nor artemisinin showed any antibacterial activity against the xenic bacteria accompanying the six H. meleagridis clones at concentration levels identical to the antihistomonal setting. The dichloromethane extract of dry leaves (Ext-DCM) (minimal lethal concentration=1.0 mg/ml) and artemisinin (half-maximal inhibitory concentration=1.295 mg/ml) had the most promising antihistomonal properties and were therefore subsequently tested in a standardized experimental infection model in both turkeys and chickens infected with clonal H. meleagridis. There were no differences between treatment groups, where all infected turkeys showed severe clinical histomonosis and demonstrated severe typhlohepatitis typical for histomonosis. Consistent with the infection model used, the infected chickens did not show any adverse clinical signs but contracted severe lesions in their caeca 7 and 10 days post infection (d.p.i.), liver lesions were absent to mild after 7 d.p.i. and progressed to severe lesions at 10 d.p.i.; thus no differences between treatment groups were observed. In conclusion, neither artemisinin nor Ext-DCM was able to prevent experimental histomonosis in turkeys and chickens at the given concentrations, which is contrary to the antihistomonal effect noticed in vitro even though the same clonal culture was used. The results of this study therefore clearly demonstrate the importance of defined in vivo experimentation in order to assess and verify in vitro results.