Clostridium botulinum - Botulism in aquatic birds: types of toxins involved, epidemiology and diagnostic methods in IVAMI
Botulism is caused by ingestion of a potent neurotoxin produced by some strains of Clostridium botulinum. The toxin can also be produced by the colonization of the gut by toxin-producing strains of Clostridium botulinum. This toxin, when ingested, or when produced in the intestine, it is absorbed from the gastrointestinal tract and affects neuromuscular transmission, blocking neuromuscular junctions and stopping the release of the neurotransmitter acetylcholine. As a result causes flaccid paralysis, eventually followed by death.
Avian botulism is diagnosed worldwide and is considered the most important in terms of avian disease mortality. Of the seven types of botulinum toxin (A to G), the type C is the most commonly involved, followed by types D and E. Some cases due to toxin mosaic C and D, it has proven more lethal for inoculated mice.
Clostridium botulinum can be found in the sediments of lakes in some arthropods (such as carrion flies), and aquatic snails. When the animals die from botulism, or otherwise, the flies scavengers larvae ingest the toxin, and are not affected by it, but can be a carrier for other birds which ingest these larvae from carcasses. From any of these sources may become colonized waterfowl, and has been possible to demonstrate the presence of Clostridium botulinum in the digestive tract of up to 38% of waterfowls. It has also been found in some studies on aquatic invertebrates (18%) and Ghouls invertebrates (33%) like flies Sarcophagidae and Calliphoridae. The presence of the bacteria in adult flies opens a new perspective on the epidemiology of avian botulism because flies can transmit Clostridium botulinum from a housing to another. It has also demonstrated the presence of Clostridium botulinum in aquatic snails from which can colonize the birds when they eat them .
Clostridium botulinum proliferates in poultry carcasses, and are ingested by maggoty that contains toxins and can affect healthy birds that consume it.
In this regard it has been proposed the removal of dead birds carcasses to try to reduce its effect on the epidemiological chain, but the results have not been conclusive. The survival of some waterfowl can be higher in lakes sparsely cases, but has not shown a significant effect of the withdrawal of the housings.
In outbreaks of botulism there are several predisposing factors that have complex relationships:
- The abundance of Clostridium botulinum spores in the medium may depend on the type of soil, aquatic sediments and water properties.
- The high temperatures reached in wetlands, especially in summer, which may favor the development of Clostridium botulinum in decaying materials.
- The bird mortality due to other causes, may contribute to botulism that provides housing where Clostridium botulinum can grow and start an outbreak.
- The susceptibility of some bird species to botulinum toxin can be a determining factor.
The diagnosis of avian botulism through two basic options: 1) detecting botulinum toxin pre-formed in the blood of the animal, and 2) culturing Clostridium botulinum from the gut or the medium where the birds, are affected showing that it is producing botulinum toxin.
In this sense, detect botulinum toxin in the blood of an affected bird is feasible only when you have the affected bird alive, because otherwise the invasion of the bloodstream by bacteria from the gut, makes it almost impossible to correctly inoculate mice.
If you wish to detect the presence of Clostridium botulinum in aquatic sediments or in the digestive tract (intestinal contents of the cecum) of the birds, fly larvae, aquatic arthropods, aquatic snails, etc., it is recommended to perform a culture, and after several days (7-9 days), obtain a culture filtrate, to inoculate to mice, or preferably today, detect the presence of the toxin producing genes in the culture of bacteria. We say it is preferably detect genes because many bacteria in the culture through its endotoxins, although the culture supernatant can be filtered, can lead to death of the mice. Moreover, the specific detection of genes for each type of toxin, rules out the neutralization test in mice to identify the type of toxin, so that the test result isearlier.
Tests at IVAMI
- Toxin detection in blood of sick animals before death.
- Culture isolation of Clostridium botulinum from samples of aquatic sediments, intestinal content (preferably from the cecum).
- Detection of toxin in culture, by inoculating mice or detection of the genes encoding the toxin by PCR.
- Those previously indicated in each test.
Preservation and shipment of sample:
- Refrigerated (preferred) for less than 2 days.
- Detection of toxin in blood: 48 to 72 hours.
- Clostridium botulinum culture and presence of toxin in crops: 9 to 10 days.
Cost of the test:
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