Asymptomatic Carriage of C. botulinum Type D/C in Broiler Flocks as the Source of Contamination of a Massive Botulism Outbreak on a Dairy Cattle Farm

Navigating the Complexities Involving the Identification of Botulinum Neurotoxins (BoNTs) and the Taxonomy of BoNT-Producing Clostridia

Botulinum neurotoxins are a varied group of protein toxins that share similar structures and modes of activity. They include at least seven serotypes and over forty subtypes that are produced by seven different clostridial species. These bacterial species are not limited strictly to BoNT-producers as neuro-toxigenic and non-neuro-toxigenic members have been identified within each species. The nomenclature surrounding these toxins and associated bacteria has been evolving as new isolations and discoveries have arisen, resulting in challenges in diagnostic reporting, epidemiology and food safety studies, and in the application of therapeutic products. An understanding of the intricacies regarding the nomenclature of BoNTs and BoNT-producing clostridia is crucial for communication that allows for accurate reporting of information that is pertinent to each situation.

Exposure of waterfowl to Clostridium botulinum in France

Botulism in wild birds is a widespread and potentially lethal disease raising major conservation issues. Botulism is also of public health concern. Due to the action of botulinum neurotoxins, mostly produced by Clostridium botulinum, botulism can affect wild birds, livestock, and humans. This study is part of a project aimed at improving our understanding of the pathogenesis of botulism in wild avifauna, which is still poorly understood. Indeed, the prevalence and dynamics of C. botulinum in the digestive tract or in bird tissue, whether as intermittent carriage related to environmental contamination or as part of the normal avian microbiota, is still unknown. In this study, we specifically addressed the presence of a healthy carrier status of wild birds, and its role in outbreaks. To answer this question, we monitored the estimated prevalence of C. botulinum in wild birds through samples from banded and swabbed birds as well as from hunted bird organs. Our results do not support the hypothesis of a healthy carriage outside of outbreaks, which raises the question of the bioavailability of the bacterium and toxin in the environment. Finally, the gene encoding botulinum neurotoxin type E was detected in keel muscle from a hunted bird, showing that recommendations on the consumption of wild bird meat are needed following a botulism outbreak.

Clostridium botulinum type C, D, C/D, and D/C: An update

Clostridium botulinum is the main causative agent of botulism, a neurological disease encountered in humans as well as animals. Nine types of botulinum neurotoxins (BoNTs) have been described so far. Amongst these "toxinotypes," the A, the B and E are the most frequently encountered in humans while the C, D, C/D and D/C are mostly affecting domestic and wild birds as well as cattle. In France for instance, many cases and outbreaks are reported in these animal species every year. However, underestimation is very likely at least for avifauna species where the detection of dead animals can be challenging. Knowledge about BoNTs C, D, C/D, and D/C and the diseases they cause in animals and humans is still scarce and unclear. Specifically, the potential role of animal botulism outbreaks in cattle and poultry as a source of human illness needs to be further assessed. In this narrative review, we present the current knowledge about toxinotypes C, D, C/D, and D/C in cattle and poultry with, amongst various other aspects, their epidemiological cycles. We also discuss the zoonotic potential of these toxinotypes and some possible ways of risk mitigation. An adapted and effective management of botulism outbreaks in livestock also requires a better understanding of these less common and known toxinotypes.

Prevalent toxin types of Clostridium botulinum in South Korean cattle farms

•

C. botulinum types B, C/D, and D are prevalent in South Korean cattle farms.

•

Botulinum toxin type B is dominant in cow feeds in South Korean cattle farms.

•

Botulinum toxin type D is dominant in cow feces in South Korean cattle farms.

Clostridium botulinum produces neurotoxic substrates that can cause fatal flaccid paralysis called botulism. These neurotoxins are classified into types A–G. Several botulism cases were recorded in 2012–2013 in the Gyeonggi province, South Korea. We assessed the distribution of C. botulinum types B, C, and D in several South Korean farms. A total of 184 samples collected in 2012–2013, including feces (n = 72), hay and silage (n = 50), soil (n = 26), water trough (n = 21), and stomach contents (n = 15), were subjected to multiplex polymerase chain reaction (PCR) to screen for types B, C, and D. Twenty-four samples tested PCR-positive as follows: type B (n = 11), type C/D (n = 4), and type D (n = 18). Eight of the 11 type B samples were detected in hay and silage. Sixteen of the 18 type D samples were detected in fecal and stomach content samples. PCR-positivity was observed in fecal (n = 9, 12.5%), hay and silage (n = 10, 20.0%), water trough (n = 2, 9.5%), and stomach content (n = 12, 80.0%) samples. Fourteen (42.4%) C. botulinum-positive samples were isolated from the PCR-positive samples (type B [n = 8], type C/D [n = 1], and type D [n = 5]). Our findings demonstrate that C. botulinum types B, C/D, and D were prevalent in South Korean cattle farms between 2012 and 2013.

Candidate vectors of horizontal transfer of BovB retrotransposon

The horizontal transfer of retrotransposons has a significant impact on the regulatory system of a multicellular organism, but the biological basis of horizontal transfer has been sufficiently studied up to date. Earlier, we identified the conserved sequence of retrotransposons recombination products of the bovine chromosome 1 nucleotide sequence region. This conserved sequence has a high percent identity with LINE BovB, which is widely known as horizontal transfer participant. The current study analyzes the presence of the conserved sequence of retrotransposons recombination products of cattle in members of different taxonomic groups to detect potential vectors of horizontal transfer. It was shown that the conserved sequence with a high percent identity can be found in 43 members of different species, including eukaryotes, prokaryotes and viruses. The identified potential vectors of horizontal retrotransposon transfer associated with various diseases of farm animals are of particular interest. Such potential vectors are hemiparasites Babesia ovata and Babesia bigemina (pathogens causing babesiosis), bacterium Clostridium botulinum (the causative agent of botulism), Jaagsiekte sheep retrovirus (the causative agent of lung cancer in sheep). They all have regions with a high percent identity (not lower than 95%) to the studied bovine conserved sequence. Thus, we identify new potential vectors of horizontal retrotransposon transfer as well as the possible influence of retrotransposons on regulatory networks affecting host protection from infectious diseases.

A Four-Monoclonal Antibody Combination Potently Neutralizes Multiple Botulinum Neurotoxin Serotypes C and D

Human botulism can be caused by botulinum neurotoxin (BoNT) serotypes A to G. Here, we present an antibody-based antitoxin composed of four human monoclonal antibodies (mAbs) against BoNT/C, BoNT/D, and their mosaic toxins. This work built on our success in generating protective mAbs to BoNT /A, B and E serotypes. We generated mAbs from human immune single-chain Fv (scFv) yeast-display libraries and isolated scFvs with high affinity for BoNT/C, BoNT/CD, BoNT/DC and BoNT/D serotypes. We identified four mAbs that bound non-overlapping epitopes on multiple serotypes and mosaic BoNTs. Three of the mAbs underwent molecular evolution to increase affinity. A four-mAb combination provided high-affinity binding and BoNT neutralization of both serotypes and their mosaic toxins. The mAbs have potential utility as therapeutics and as diagnostics capable of recognizing and neutralizing BoNT/C and BoNT/D serotypes and their mosaic toxins. A derivative of the four-antibody combination (NTM-1634) completed a Phase 1 clinical trial (Snow et al., Antimicrobial Agents and Chemotherapy, 2019) with no drug-related serious adverse events.