What is Botulism?
Botulism is a rare but serious paralytic illness caused by a neurotoxin secreted by certain strains of Clostridium botulinum, also known by shorthand form C. botulinum. Foodborne botulism is the most lethal bacterial toxin-mediated foodborne disease, and occurs with relatively low frequency. Botulism is also the only disease of that class for which a specific effective therapy exists (Giannella, 2010).
The term botulism comes from botulus, the Latin word for sausage. The term makes sense when one considers that the first recognized botulism cases were linked to improperly prepared blood sausage in late 18th century Germany (Schwartz and Morgan, 2007). In 1897, researchers first linked the C. botulinumorganism to botulism, the disease that it manifests, following an outbreak caused by uncooked ham that sickened 23 music club patrons in Belgium (Schwartz and Morgan, 2007).
According to the CDC, there are five main kinds of botulism:
- Foodborne botulism, which is caused by eating foods that contain the toxin;
- Wound botulism, caused by toxin produced from a wound infected with Clostridium botulinum;
- Infant botulism, caused by consuming the spores of the bacteria, which then grow in the intestines and release botulinum toxin;
- Adult intestinal toxemia botulism, also called adult intestinal colonization botulism, which occurs when an adult consumes botulinum bacteria spores which subsequently grow in the intestines and release botulinum toxin;
- Iatrogenic botulism, which results from an accidental overdose of botulinum toxin (CDC, 2010).
All forms of botulism can be fatal and are considered medical emergencies. Foodborne botulism can be especially dangerous because many people can be poisoned by eating a contaminated food, and all cases of foodborne botulism are treated as a public health emergency due to the risk that the food – homemade or commercially available – responsible for causing the illness may still be available for consumption and sicken other unsuspecting people (CDC, 2010).
What kind of bacteria is Clostridium Botulinum?
C. botulinumis the name of a group of bacteria commonly found in soil. These rod-shaped organisms grow best in low oxygen conditions. The bacteria form spores which allow them to survive in a dormant state until exposed to conditions that can support their growth.
There are seven types of botulism toxin designated by the letters A through G. Only types A, B, E and F cause illness in humans (CDC, 2010). Types A, B, and E cause almost all cases of human botulism; botulism from exposure to a type F strain is very rare (Schwartz and Morgan, 2007). Toxin types C and D generally cause botulism in birds and mammalian animals (Schwartz and Morgan, 2007).
The neurotoxin produced by C. botulinum is the most lethal toxin known to mankind (Pigott, 2008). In fact, one nanogram (one billionthof a gram) per kilogram of body weight will paralyze a person, even if they are otherwise totally healthy (Crawford, 2011). The CDC considers it a Category A agent, which is the classification given to the most dangerous bioterrorism agents (Pigott, 2008).
Botulism most commonly occurs during the summer and fall months (Sodha et al., 2010). Type A botulism is most commonly encountered in regions west of the Mississippi River (Sodha et al., 2010; Long, 2008). Type B spores are found almost exclusively to the area between 35 and 55 degrees north latitude, and generally are found in soils with high organic content (Long, 2008). Type E-producing bacteria occur in sediments around bodies of fresh water and in marine life, particularly around the Great Lakes and Alaska (Long, 2008). As a result, type E infection is most common in Alaska (Sodha et al., 2010; Shapiro et al., 1998). Type F botulism strains have also been isolated from Pacific Coast marine sediment, as well as from Chesapeake Bay crabs (Long, 2008).
The strain of botulism may determine the severity of the disease. Respiratory failure requiring ventilation occurs significantly more often in cases of type A botulism (Schwartz and Morgan, 2007). Type E botulism requires intubation and mechanical ventilation in the smallest percent of cases; however, it should also be noted that the incubation for type E botulism is substantially shorter than that of other types, and almost all individuals infected with type E botulism experience their first symptoms within 24 hours of ingesting the toxin (Schwartz and Morgan, 2007). Type B has the longest incubation period of A, B, and E, and the severity of the disease falls between that caused by types A and E (Schwartz and Morgan, 2007).
After consumption, botulinum toxin travels to the small intestine, where it is absorbed. After being absorbed, it travels throughout the body via the circulatory and lymphatic systems (Schwartz and Morgan, 2007). C. botulinum-produced toxins work by rapidly and permanently binding to receptors on motor nerve terminals (Pigott, 2008). Motor nerves control both voluntary (for example, walking) and involuntary (for example, breathing) bodily movements. In order for these movements to happen, signals have to be sent from neuron to the target muscle cells; chemicals called neurotransmitters deliver these signals (Crawford, 2011; Pigott, 2008). When the toxin binds to the receptor, it prevents it from releasing the neurotransmitter acetylcholine (Pigott, 2008). When enough receptors are blocked, the message cannot get through and the muscles cannot respond.
How does Botulism spread?
Botulism is most frequently associated with consumption of low acid fruits, vegetables, and fish canned at home. In this case, “low acid” means that a substance has a pH greater than or equal to 4.4 (Sodha et al., 2010).
Recently, outbreaks of botulism were tied to commercially-distributed canned chili sauce and bottled carrot juice; these botulism outbreaks were the first tied to commercially distributed products in about 20 years (Sodha et al., 2010; CDC, 2006). Past outbreaks and cases have also been linked to consumption of more unusual vehicles of transmission, including baked potatoes, chopped garlic in oil, chicken pot pie, turkey loaf, cheese sauce, beef stew, salsa, and sautéed onions (Giannella, 2010; Sodha et al., 2010; Schwartz and Morgan, 2007; Shapiro et al., 1998). Restaurant-associated outbreaks of botulism have accounted for a large portion of botulism cases in the United States since the 1970s (Sobel et al., 2004). In fact, 40% of botulism cases have been traced to restaurant-associated outbreaks (Schwartz and Morgan, 2007).
A large number of cases result from home-canned foods with low acid content, such as beets, corn, green beans, and asparagus (CDC, 2010). Due to the incredibly low infectious dose, one bite of contaminated food may be sufficient to cause clinical illness (Fernandez-Frackelton, 2010).
A number of infant botulism cases resulted from honey consumption; as a result, medical sources advise parents to refrain from serving honey to their infants (Sodha et al., 2010).
How common is Botulism?
In the United States an average of 145 cases of botulism are reported each year (CDC, 2010). Of these, approximately 15% are foodborne, 65% are infant botulism, and the rest are wound botulism (CDC, 2010). Outbreaks of foodborne botulism involving two or more persons generally occur at least once a year and usually result from eating contaminated home-canned foods. The number of cases of foodborne and infant botulism has changed little in recent years, but wound botulism has increased.
All individuals are at risk for botulism. Those who use drugs intravenously (injection drug users) have an increased risk of wound botulism (CDC, 2010). Those who eat home-canned food may also increase their risk of contracting the disease.
In Alaska, the rates of botulism are the highest of any state in the U.S.; 39% of botulism cases that occurred between 1990 and 2000 took place in Alaska (Sobel et al., 2004). Nearly all cases of botulism in Alaska occur among Alaska Natives and result from eating fermented foods such as fermented fish heads, beaver tail or sea mammals – such as seal and whale – preserved using traditional methods (CDC, 2010; Giannella, 2010).
What are the symptoms of botulism?
In foodborne botulism, symptoms generally begin 18 to 36 hours after eating a contaminated food, but they can occur as early as 6 hours or as late as 10 days (CDC, 2010). The amount of time between ingestion and development of symptoms depends on the amount of botulinum toxin ingested: the more toxin ingested, the more quickly symptoms will develop. The first symptoms of botulism generally are gastrointestinal and may include nausea, vomiting, diarrhea, and abdominal pain (Schwartz and Morgan, 2007). After neurological symptoms develop, constipation often develops (Giannella, 2010).
The four most common neurological symptoms are dysarthria (difficulty annunciating or slurred speech), visual disturbances (such as double or blurred vision), dysphagia (difficulty swallowing), and dry mouth (Schwartz and Morgan, 2007). Other neurological symptoms include headache, malaise, generalized weakness, dizziness, and paresthesias (the sensation that one’s skin is tingling, prickling, or numb) (CDC, 2010; Schwartz and Morgan, 2007).
As the disease progresses, oculobulbar symptoms develop; these symptoms occur with very high frequency in botulism cases. Blurred vision, ptosis (droopy eyelid), and lateral rectus palsy occur in most patients who develop neurological symptoms; fixed or dilated pupils occur in almost 50% of patients (Schwartz and Morgan, 2007). Paralysis then descends down the body, accompanied by progressive respiratory weakness; this respiratory weakness often develops into respiratory failure (Schwartz and Morgan, 2007).
How is botulism diagnosed?
If a patient’s symptoms suggest that they may have botulsim, physicians should consider the possibility that the individual does indeed have the disease. However, these symptoms are often not enough to allow a diagnosis of botulism. In fact, about 10.5% of suspected botulism cases reported to the CDC are ultimately diagnosed as Guillain-Barré syndrome (Schwartz and Morgan, 2007). Other diseases are often commonly confused with botulism: 3.4% of suspected and reported botulism cases end up diagnosed as carbon monoxide poisoning, 3.2% as due to foodborne poisons of unknown etiology, and 3% as staphylococcal food poisoning (Schwartz and Morgan, 2007).
Other diseases commonly confused with botulism include stroke and myasthenia gravis. In order to prevent such a misdiagnosis, special tests may be run to exclude these other conditions. These tests may include a brain scan, spinal fluid examination, nerve conduction test (electromyography, or EMG), and a tensilon test for myasthenia gravis.
The most direct way to confirm the diagnosis is to demonstrate the botulinum toxin in the patient’s serum or stool by injecting serum or stool into mice and looking for signs of botulism, a process called a mouse bioassay (Reddy and Bleck, 2010). The bacteria can also be isolated from the stool of persons with foodborne and infant botulism. These tests can be performed at some state health department laboratories and at CDC (CDC, 2010). Laboratory confirmation through testing of clinical specimens can be obtained only in approximately 70-75% of botulism cases (Sodha et al., 2010; Woodruff et al., 1992).
How can botulism be treated?
Immediately upon forming the suspicion that a patient is suffering from botulism, the treating physician should call the state health department’s 24-hour emergency phone number and report the case to the state’s health department. The health department will then contact the CDC, which will arrange for a clinical consultation via telephone. If the consultation indicates it is warranted and the physician so requests, then the CDC will release botulinum antitoxin (Sodha et al., 2010). The antitoxin binds to botulism toxins type A, B, and E. By binding to the toxins, the antitoxin prevents the botulinum toxin from binding to the receptors on motor nerve terminals (Pigott, 2008).
Once the toxin binds to presynaptic nerve terminals, the antitoxin cannot displace it, making rapid administration of antitoxin extremely important. Studies show that once symptoms develop, the effectiveness of the antitoxin decreases greatly. In one study of 134 cases of botulism, researchers found a 10% mortality rate when antitoxin was administered early in the progression of the disease, a 15% mortality rate when antitoxin was administered more than 24 hours after onset of symptoms, and a 46% mortality rate among individuals who did not receive any antitoxin (Giannella, 2010). Antitoxin also decreases average time needed for recovery. Infected individuals receiving antitoxin averaged a 10-day hospital stay, whereas those that did not receive antitoxin stayed in the hospital for an average of 56 days (Giannella, 2010).
The paralysis that occurs with severe botulism requires intensive medical and nursing care. After several weeks, the paralysis slowly improves (CDC, 2010).
Physicians may try to remove contaminated food still in the gut by inducing vomiting or by utilizing enemas. Wounds should be treated, usually surgically, to remove the source of the toxin-producing bacteria. Good supportive care in a hospital is the mainstay of therapy for all forms of botulism. Currently, antitoxin is not routinely given for treatment of infant botulism (CDC, 2010).
Are there complications from botulism?
Botulism can result in death due to respiratory failure. However, in the past 50 years, the proportion of patients with botulism who die has fallen from about 50% to 3-5% (CDC, 2010). A patient with severe botulism may require a breathing machine as well as intensive medical and nursing care for several months. Patients who survive an episode of botulism poisoning may have fatigue and shortness of breath for years after the acute illness (CDC, 2010).
How can botulism be prevented?
You can decrease your chances of getting botulism by:
- Boiling home-canned food for 10 minutes prior to eating it;
- Following strict hygienic procedures and using pressure canners and pressure cookers when canning your own food at home;
- Refrigerating oils infused with garlic or herbs;
- Keeping potatoes baked in aluminum foil hot (not just warm) until eaten or refrigerated;
- Not feeding honey to infants under 12 months old;
- Not opening food containers that appear to bulge, as they may contain gas produced by botulinum; and
- Not tasting food that appears to be spoiled.
(CDC, 2010; Reddy and Bleck, 2010; Arnon, 2007).