Botulism

Therapeutic Applications of Botulinum Neurotoxins in Veterinary Medicine

Botulinum neurotoxins (BoNTs) are emerging as multipurpose therapeutic compounds for the treatment of several different syndromes involving peripheral and central nervous systems, and muscular and musculoskeletal disorders both in human and veterinary medicine. Therefore, the study of BoNTs is rapidly developing and identifying newly produced BoNT variants. Efforts should be made to clarify the biological and pharmacological characteristics of these novel BoNTs as well as the natural ones. The high potential of BoNTs as a therapeutic compound for medical syndromes lies in its ability to reach a specific cell type while bypassing other cells, thus having mild or no side effects. In this paper the recent developments in BoNTs are reviewed with the aim of analyzing the current knowledge on BoNTs' biological mechanisms of action, immunogenicity, formulations, and therapeutic applications in the veterinary field, highlighting advantages and drawbacks and identifying the gaps to be filled in order to address research priorities.

Clostridial Diseases (Botulism and Tetanus)

Botulism and tetanus are the 2 primary manifestations of neurologic disease caused by clostridial toxins. Only a small dose of clostridial toxin is required to induce severe, and often fatal, disease. Consequently, definitive diagnosis of either disease is nearly impossible to achieve antemortem or postmortem; presumptive diagnosis is usually made based on physical and neurologic examination findings. Because the severity of clinical signs can worsen rapidly, prognosis worsens when therapeutic intervention is delayed. Highly effective vaccines are available against both botulism and tetanus and are critical in preventative approaches to control.

Pathologic Conditions of the Nervous System in Horses

The variety of neurologic diseases which affect horses makes pathologic examination of the nervous system a complex and lengthy process. An understanding of the common causes of neurologic disease, antemortem neurolocalization, and supplementation of the necropsy examination with ancillary testing will help to diagnose a large number of causes of neurologic disease. A general understanding of neuropathology and collaborative relationship with your local pathologists will aid in the definitive diagnosis of neurologic diseases.

Public Health Risk Associated with Botulism as Foodborne Zoonoses

Botulism is a rare but severe neurological disease in man and animals that is caused by botulinum neurotoxins (BoNTs) produced by Clostridium botulinum and atypical strains from other Clostridium and non-Clostridium species. BoNTs are divided into more than seven toxinotypes based on neutralization with specific corresponding antisera, and each toxinotype is subdivided into subtypes according to amino acid sequence variations. Animal species show variable sensitivity to the different BoNT toxinotypes. Thereby, naturally acquired animal botulism is mainly due to BoNT/C, D and the mosaic variants CD and DC, BoNT/CD being more prevalent in birds and BoNT/DC in cattle, whereas human botulism is more frequently in the types A, B and E, and to a lower extent, F. Botulism is not a contagious disease, since there is no direct transmission from diseased animals or man to a healthy subject. Botulism occurs via the environment, notably from food contaminated with C. botulinum spores and preserved in conditions favorable for C. botulinum growth and toxin production. The high prevalence of botulism types C, D and variants DC and CD in farmed and wild birds, and to a lower extent in cattle, raises the risk of transmission to human beings. However, human botulism is much rarer than animal botulism, and botulism types C and D are exceptional in humans. Only 15 cases or suspected cases of botulism type C and one outbreak of botulism type D have been reported in humans to date. In contrast, animal healthy carriers of C. botulinum group II, such as C. botulinum type E in fish of the northern hemisphere, and C. botulinum B4 in pigs, represent a more prevalent risk of botulism transmission to human subjects. Less common botulism types in animals but at risk of transmission to humans, can sporadically be observed, such as botulism type E in farmed chickens in France (1998-2002), botulism type B in cattle in The Netherlands (1977-1979), botulism types A and B in horses, or botulism type A in dairy cows (Egypt, 1976). In most cases, human and animal botulisms have distinct origins, and cross transmissions between animals and human beings are rather rare, accidental events. But, due to the severity of this disease, human and animal botulism requires a careful surveillance.

The First Case of Botulism in a Donkey

Botulism, a severe neuroparalytic disease that can affect humans, all warm-blooded animals, and some fishes, is caused by exotoxins produced by ubiquitous, obligate anaerobic, spore-forming bacteria belonging to the genus Clostridium and named botulinum neurotoxin (BoNT)-producing clostridia. This report presents the case of a 3-year-old donkey mare referred for progressive and worsening dysphagia of four days’ duration. Her voluntary effort in eating and drinking was conserved, and she was able to slow chew without swallowing. A complete neurological examination was performed, and botulism was strongly suspected. The ability to swallow feed and water returned on the tenth day of hospitalization and improved progressively. The jenny was discharged from the hospital after fifteen days. During the hospitalization, the Italian National Reference Centre for Botulism confirmed the diagnosis: mare’s feces were positive for BoNT/B and Clostridium botulinum type B.

Equine feed contamination and toxicology

Feed as a cause of poisoning in horses can occur on small or large scales. It is challenging to work up cases of suspected feed contamination, but there are resources available to veterinarians and owners. Feed contamination can be chemical or biological. This article focuses on and provides examples of chemical feed contamination including misformulation, adulteration, and natural contaminants. Additionally, recommendations for feed sampling and diagnostic submission, including legal documentation, are included.

Botulism (type A) in a horse - case report

This paper presents the case of a six year-old, male, thoroughbred horse with clinical signs of inappetence, weakness, and incoordination when walking. Clinical examination showed that the horse staggered and leaned to the left side. Feedstuff was present inside and around its mouth. Salivation was increased and there was no reflex at the palpebrae and tongue. The horse had difficulty swallowing and the tone of its tail was reduced. Botulism was diagnosed based on the clinical signs. Antibiotic (ceftiofur) and fluid-electrolyte treatment was commenced. Next day, neostigmin was added to the horse’s treatment, and it became recumbent. The horse’s palpebral, tongue and tail reflexes returned partially after neostigmine methylsulphate treatment on the same day and it stood up on day four. However, it could not swallow anything during the whole week, so after getting permission from the owner, the horse was euthanized on day 10. Samples of the colonic content and blood serum were sent by courier to the laboratory for toxin neutralization, however, botulinum neurotoxins could not be detected. After that, serum samples from days 6 and 10 were sent to another laboratory for testing for botulinum neurotoxin antibodies by ELISA. Specific antibodies against botulinum neurotoxin type A were measured, indicating a previous, immuno-relevant contact with the toxin. This seroconversion for type A supports the clinical botulism diagnosis. Type A botulism is rarely seen in Europe and has been detected in a horse in Turkey for the first time.

Clostridial toxins

Clostridia produce the highest number of toxins of any type of bacteria and are involved in severe diseases in humans and other animals. Most of the clostridial toxins are pore-forming toxins responsible for gangrenes and gastrointestinal diseases. Among them, perfringolysin has been extensively studied and it is the paradigm of the cholesterol-dependent cytolysins, whereas Clostridium perfringens epsilon-toxin and Clostridium septicum alpha-toxin, which are related to aerolysin, are the prototypes of clostridial toxins that form small pores. Other toxins active on the cell surface possess an enzymatic activity, such as phospholipase C and collagenase, and are involved in the degradation of specific cell-membrane or extracellular-matrix components. Three groups of clostridial toxins have the ability to enter cells: large clostridial glucosylating toxins, binary toxins and neurotoxins. The binary and large clostridial glucosylating toxins alter the actin cytoskeleton by enzymatically modifying the actin monomers and the regulatory proteins from the Rho family, respectively. Clostridial neurotoxins proteolyse key components of neuroexocytosis. Botulinum neurotoxins inhibit neurotransmission at neuromuscular junctions, whereas tetanus toxin targets the inhibitory interneurons of the CNS. The high potency of clostridial toxins results from their specific targets, which have an essential cellular function, and from the type of modification that they induce. In addition, clostridial toxins are useful pharmacological and biological tools.

Botulism: cause, effects, diagnosis, clinical and laboratory identification, and treatment modalities

Botulism is a neuroparalytic disease caused by neurotoxins produced by the bacteria Clostridium botulinum. Botulinum neurotoxins (BoNTs) are among the most potent naturally occurring toxins and are a category A biological threat agent. The 7 toxin serotypes of BoNTs (serotypes A-G) have different toxicities, act through 3 different intracellular protein targets, and exhibit different durations of effect. Botulism may follow ingestion of food contaminated with BoNT, from toxin production of C botulinum present in the intestine or wounds, or from inhalation of aerosolized toxin. Intoxication classically presents as an acute, symmetrical, descending flaccid paralysis. Early diagnosis is important because antitoxin therapy is most effective when administered early. Confirmatory testing of botulism with BoNT assays or C botulinum cultures is time-consuming, and may be insensitive in the diagnosis of inhalational botulism and in as many as 32% of food-borne botulism cases. Therefore, the decision to initiate botulinum antitoxin therapy is primarily based on symptoms and physical examination findings that are consistent with botulism, with support of epidemiological history and electrophysiological testing. Modern clinical practice and antitoxin treatment has reduced botulism mortality rates from approximately 60% to < or =10%. The pentavalent botulinum toxoid is an investigational product and has been used for more than 45 years in at-risk laboratory workers to protect against toxin serotypes A to E. Due to declining immunogenicity and potency of the pentavalent botulinum toxoid, novel vaccine candidates are being developed.

Neurologic Disorders of Neonatal Foals

Neurologic examination of the neonatal foal is quite different from the process used to examine older foals and adult horses. Abnormal neurologic signs are best appreciated in the context of a detailed knowledge of general neonatal medicine and awareness of nor-mal foal behavior and milestones of development. A systematic approach to neurologic examination is provided. The results of such examination are used to localize a lesion or lesions in the nervous system. Descriptions and treatment strategies are given for most common and important neonatal neurologic diseases.

Botulism in foals less than 6 months of age: 30 cases (1989-2002)

Botulism has been recognized as a clinical entity in foals since the 1960s. Also known as "Shaker foal" disease, the toxicoinfectious form of botulism affects foals, with the highest incidence in the United States seen in Kentucky and the mid-Atlantic region. The disease is characterized by progressive muscular weakness caused by the action of botulism neurotoxin at cholinergic neuromuscular junctions. Increased number of episodes and duration of recumbency, muscular trembling, and dysphagia are seen in affected foals. Left untreated, the disease can be rapidly fatal, with death occuring secondary to respiratory muscle paralysis within 24 to 72 hours of the onset of clinical signs. Very mildly affected foals can survive with minimal treatment Despite advances made in treatment of these foals, including administration of botulism antitoxin early in the course of the disease, there is still an impression that the disease carries a high mortality rate. The purpose of this study was to evaluate outcome in 30 foals <6 months of age diagnosed with botulism between 1989 and 2002 at the George D. Widener Large Animal Hospital, New Bolton Center. Two foals were euthanized for economic reasons early in the disease course, and I died while being treated. Survival of treated cases was greater than 96%. Approximately 50% of the cases required oxygen therapy, whereas 30% required mechanical ventilation. All foals, excepting 1 mildly affected foal, received botulism antitoxin. Mean duration of hospitalization was 14 days. With appropriate treatment, foals with botulism have a high survival rate.

Evaluation of a botulinum fragment C-based ELISA for measuring the humoral immune response in primates

An enzyme-linked immunosorbent assay (ELISA) using botulinum neurotoxin serotype B recombinant fragment C (rBoNTB(HC)) was developed to measure specific humoral immune responses of monkeys vaccinated with a vaccine consisting of rBoNTB(HC). Several fundamental parameters for a bioassay were evaluated. The evaluation results demonstrated that using BoNTB(HC) as the capture antigen led to a specific and sensitive ELISA for botulinum type B antibody with excellent precision, accuracy, and linearity. There was a good correlation (r=0.91) between ELISA titers and neutralization bioassay titers. Experimental results suggested that the ELISA could be useful for detecting botulinum type B antibody levels and may supplement mouse neutralization bioassays during planned clinical manufacturing and clinical trials of rBoNTB(HC) vaccine.

Botulism in the horse

Botulism should be considered in cases where weakness, paralysis, or intolerance to exercise might be seen in the horse. Dysphagia may also be present, although it is not a consistent finding. Potential sources include carrion in hay, moldy or otherwise rotted vegetation or forage, birds carrying material from animal burial or other similar sites, and contaminated carcasses on-site. Horses, especially foals, may also suffer from toxicoinfectious botulism, a condition where the C. botulinum might colonize and produce toxin within the gastrointestinal tract. Wounds also may harbor the organism and otherwise promote botulism. Diagnosis of botulism is often a clinical diagnosis backed up by elimination of other possible infectious, injurious, or toxic causes of weakness of the horse. Definitive diagnosis and type identification in the laboratory are difficult and usually require a suitable sample of the source material. Treatment often is unrewarding unless a case is identified early and the proper antitoxin is readily available. Prevention involves common sense approaches to feeding and care of the horse and, where possible, judicious use of vaccination in endemic areas.

Borna disease in horses

Borna disease is a sporadically occurring, progressive viral polioencephalomyelitis that primarily affects horses and sheep. The etiological agent, Borna disease virus (BDV), is an enveloped, single-stranded RNA virus that has been classified in the new virus family Bornaviridae within the order Mononegavirales. Serological evidence of BDV infection has been found in an increasing number of countries throughout the world. After an incubation period lasting a few weeks to several months, BDV infection can cause locomotor and sensory dysfunction followed by paralysis and death. Borna disease is the result of a virus-induced immunopathological reaction. BDV-specific antibodies and viral RNA have been found in humans with various psychiatric disorders.

An outbreak of type C botulism in 12 horses and a mule

A USDA Early Response Team investigated deaths of several horses and a mule in northern Arizona at the request of local animal health officials. Thirteen animals (12 horses and 1 mule) housed at 5 facilities in a 7.4 square mile area died between August 1998 and January 1999. Clinical signs consisted of muscular weakness that rapidly progressed to lateral recumbency. Ten animals had paresis of the tongue, throat, or lips. Affected animals appeared alert and were interested in eating and drinking, even while recumbent. All 13 animals were euthanatized. Clostridium botulinum type C was isolated from feces or intestinal contents from 3 affected horses. Preformed toxin was detected in samples of soil and bird droppings collected from a nearby horse burial site. It was hypothesized that the outbreak was a result of birds, presumably ravens, feeding at the burial site and at horse facilities in the area that transferred toxin to the affected animals.