The Latent Threat in Wild Birds: Clostridium botulinum

Avian botulism caused by Clostridium botulinum emerged in 1910, affecting birds across North America, leading to severe outbreaks exacerbated by climate change, decreasing water levels, and inadequate wastewater management. While deadly for birds, its epidemiological impact on humans and other animals remains limited. Despite its significance, understanding and controlling the disease remain challenging. This review delves into the pathogen's epidemiology in wild bird populations, exploring the transmission, pathogenicity, clinical symptoms, diagnosis and treatment. The disease's growing concern in wild birds relates to the bacterium's adaptability and expansive spread, evident through genetic similarities among strains across countries. Outbreaks are influenced by environmental factors such as temperature and soil characteristics. Wild birds inadvertently transmit the bacterium, perpetuating the cycle through carcasses and flies. Some species suffer severely, while others, like scavengers, show resistance. Understanding disease mechanisms, involving potential toxin ingestion or internal production, remains ongoing. Clinical signs vary, affecting diverse bird orders. Diagnostic methods evolve, with treatment success varying among affected populations. Prevention and surveillance take precedence due to treatment challenges, emphasising population-based strategies and preventive measures to manage the widespread presence of C. botulinum.

Analysis of free and metabolized microcystins in samples following a bird mortality event

In the summer of 2012, over 750 dead and dying birds were observed at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island, Maryland, USA (Chesapeake Bay). Clinical signs suggested avian botulism, but an ongoing dense Microcystis bloom was present in an impoundment on the island. Enzyme-linked immunosorbent assay (ELISA) analysis of a water sample indicated 6000 ng mL^-1 of microcystins (MCs). LC-UV/MS analysis confirmed the presence of MC-LR and a high concentration of an unknown MC congener (m/z 1037.5). The unknown MC was purified and confirmed to be [D-Leu¹]MC-LR using NMR spectroscopy, LC-HRMS and LC-MS², which slowly converted to [D-Leu¹,Glu(OMe)⁶]MC-LR during storage in MeOH. Lyophilized algal material from the bloom was further characterized using LC-HRMS and LC-MS² in combination with chemical derivatizations, and an additional 24 variants were detected, including MCs conjugated to Cys, GSH and γ-GluCys and their corresponding sulfoxides. Mallard (Anas platyrhynchos) livers were tested to confirm MC exposure. Two broad-specificity MC ELISAs and LC-MS² were used to measure free MCs, while 'total' MCs were estimated by both MMPB (3-methoxy-2-methyl-4-phenylbutyric acid) and thiol de-conjugation techniques. Free microcystins in the livers (63-112 ng g^-1) accounted for 33-41% of total microcystins detected by de-conjugation and MMPB techniques. Free [D-Leu¹]MC-LR was quantitated in tissues at 25-67 ng g^-1 (LC-MS²). The levels of microcystin varied based on analytical method used, highlighting the need to develop a comprehensive analysis strategy to elucidate the etiology of bird mortality events when microcystin-producing HABs are present.

Minimizing an outbreak of avian botulism (Clostridium botulinum type C) in Incheon, South Korea

An outbreak of botulism occurred over a two-month period beginning July 20, 2016. In all, 697 wild birds were found paralyzed or dead at the Namdong reservoir and 11 Gong-gu. Using a mouse bioassay, type C botulinum toxin was identified in the bird serum, liquid cultures of soil samples, and maggot extracts. To minimize further infection of wild birds, we opened the floodgates of the Namdong reservoir adjacent to the Yellow Sea; this decreased the water temperature and the nutrient load such as nitrogen and phosphorus. The outbreak stopped shortly after taking these actions. It is not known if these efforts decreased the number of dead and diseased wild birds. Our study demonstrates one potential approach to minimize future botulism outbreaks among wild birds and their habitats.