Mycotoxins are, more frequently than not, present in animal commodities and feed.
Out of the more than 3,300 samples tested during the 12 months of 2010, a striking 78% were positive for mycotoxin presence, a recent survey shows.
Even at low levels, mycotoxin ingestion may cause an array of metabolic disturbances resulting in poor animal health. These disturbances are often difficult to recognize because signs of the disease are associated with infection rather than with the toxin that predisposed the animal to infection, making a diagnosis of a mycotoxicosis difficult.
Because aflatoxins, especially aflatoxin B1, are potent carcinogens in some animals, there is interest in the effects of long-term exposure to low levels of these important mycotoxins on humans. In 1988, the International Agency for Research on Cancer placed aflatoxin B1 on the list of human carcinogens. This is supported by a number of epidemiological studies done in Asia and Africa that have demonstrated a positive association between dietary aflatoxins and liver cell cancer.
The effects of chronic (as opposed to acute) mycotoxin exposure on health are poorly documented in humans, much less in animals, and the economic impacts of mycotoxins have been studied primarily with respect to trade barriers, not from the perspective of farmers and their well-being.
Bertrand Grenier from the French National Institute for Agricultural Research also underlined the fact that animals are often exposed to a cocktail of mycotoxins. The mycotoxins interact which each other, explained Grenier.
Add to that, the problem of long-term exposure to combinations of mycotoxins at low concentrations may have a negative effect on animal health. At the same time, current legislation and recommendations are based on individual mycotoxins and not multi-contamination.
So what is a farmer to do, who depends on a cheap source of animal feed and continued production despite the animals failing health? Why, give them that much more antibiotics, of course.
Another problem complicating what was originally thought of as a simple expression of the toxin in the animal, Professor Dr. Sarah De Saeger from Ghent University in Belgium, talked about challenges to combat masked mycotoxins.
She explained that masked (or conjugated) mycotoxins first caught attention in the late 1980s because, in some cases of mycotoxicosis, clinical observations in animals did not correlate with the low mycotoxin content determined in the feed.
The unexpected high toxicity was therefore attributed to the occurrence of undetected, conjugated forms of mycotoxins that possibly hydrolyze to the precursor toxins in the digestive tract of animals.
But the research on masked mycotoxins has exponentially grown explained De Saeger. Different research groups are now focusing on the variety of masked mycotoxins, the occurrence, bioavailability, and toxicity of the masked forms, among others.
Aflatoxin in dairy products
Aflatoxins have received greater attention than any other mycotoxins because of their demonstrated potent carcinogenic effect in susceptible laboratory animals and their acute toxicological effects in humans.
Since only 20 ppb total aflatoxins are allowed in US human food and dairy feeds, and US milk must be less than 0.5 ppb, aflatoxin is well-monitored by most feed companies. Those that produce feed for use on their stock farms often lack the resources and motivation to test each bin, tank or silo for this known carcinogen and immunosuppressant. And there is no widespread, systematic monitoring of US dairy products for the M1 form of aflatoxin produced by animals fed mycotoxin-contaminated feed.
Mycotoxins in pets
When we include more cereals in dry pet food, the risk of mycotoxicoses also increases. Most obviously affected are dogs and cats, but mainly because cases are identified.
It is generally recognized by petfood manufacturers that mycotoxin contamination is a source of increased problems in their industry. The major mycotoxins with potential for contamination of pet foods are aflatoxins, vomitoxin, zearalenone, fumonisins, and ochratoxin A. Three genera of fungi, Aspergillus, Penicillium, and Fusarium (Gibberella), are the most frequently implicated causes of mycotoxin contamination.
The primary target organ for aflatoxins is the liver with liver disease resulting from dogs ingesting aflatoxin-contaminated dog food. Little is known about the toxicity of vomitoxin, known chemically as deoxynivalenol (DON) in pets. It is known that dogs are susceptible to relatively low levels of vomitoxin and exhibit health problems similar to those seen in swine. Cats, as well as cattle, poultry, and humans, can also be affected.
There are no reports that zearalenone has caused clinical signs in dogs or cats. Fumonisins interfere with cell membrane metabolism, and the signs of toxicity vary with species. The only studies conducted to demonstrate the effects of fumonisins in pet species have been in rabbits. Ochratoxin A is a nephrotoxin (i.e., toxic to the kidneys) and is also teratogenic (i.e., causes fetal malformation during the first three months of pregnancy) in all species tested. It also impairs the immune system and is a suspected carcinogen.
Following the links in the food chain
With the exception of aflatoxins, Federal and State requirements for routine testing of these mycotoxins are entirely inadequate to follow these poisons through the food chain. Even in the case of aflatoxins, on-farm testing is rarely applied as the regulatory focus falls on feeds and foods offered for sale after off-farm storage and processing.
What remains unknown is how much of the mycotoxin that reaches livestock is transferred to food products or measurements of the incidence of aflatoxin and zearalenone incidence in snack foods, milled grains, dairy, and meat products produced.
With this information, were it known, we could trace contamination forward and back through the food chain. The first impact would be awareness on the part of the feed and food industry, the second would be reductions based on recommendations of known steps to reduce contamination and the final step would be an experimental implementation of new techniques to keep food safe for the next generation of animals and their owners.
And finally, a reminder of the deadly consequences of pet food contaminated with aflatoxin that affected hundreds, if not thousands of pets:
Dogs keep dying: Too many owners remain unaware of toxic dog foodBy Susan S. Lang, Cornell University, January 2006
Even though Diamond, Country Value and Professional brand dog foods have been recalled for containing highly toxic aflatoxins, they have caused an estimated 100 dog deaths in recent weeks, say Cornell University veterinarians, who are growing increasingly alarmed. Some kennels and consumers around the nation remain unaware of the tainted food, which may have been shipped to more than two dozen countries, and as a result, they continue to give dogs food containing a lethal toxin.
To better screen affected dogs so they can be treated as soon as possible, Cornell veterinarians report that they now have a new test, adapted from one used in humans, to accurately assess aflatoxin poisoning in dogs (see companion story). Currently, about two-thirds of dogs that show symptoms after eating the tainted food die.
“Entire kennels have been wiped out, and because of the holiday these past few weeks, the dispersal of recall information was disrupted,” says Sharon Center, a professor of veterinary medicine who specializes in liver function and disease at the College of Veterinary Medicine at Cornell, which is emerging as a central clearinghouse for information about the dog food poisoning.
The Cornell Vet College is continually updating its website to keep the public and veterinarians informed as new information on the poisonings emerge. Cornell’s Animal Health Diagnostic Center (AHDC) is analyzing blood and liver samples from sick dogs around the country, testing suspected dog food, conducting autopsies and collecting as many livers as possible from dead dogs to confirm cause of death, tracking dogs that have died and following up on the health of dogs that survive the food poisoning. The AHDC has information for veterinarians on its Web site http://diaglab.vet.cornell.edu/news.asp.
“We suspect that dogs have been dying since November, perhaps even October, but it took the perfect storm of circumstances to get the diagnosis,” said Karyn Bischoff, the veterinary toxicologist at Cornell, who first identified aflatoxin as the culprit in the recent wave of deaths.
Trying to save dogs
Over the recent holiday weeks, Center and her staff worked around-the-clock to try to save the 17 poisoned dogs admitted to Cornell’s Hospital for Animals. “I’ve been working with liver disease in dogs for 30 years, and I’ve never seen such miserably ill dogs,” said Center, noting that severely affected dogs suffer from intractable vomiting and internal bleeding.
“Despite our understanding of this complex toxin, we have no direct antidote for this poisoning. This has been an immensely sad holiday and one that will leave an indelible mark on the owners that lost their cherished family members.”
Of those 17 dogs, Center euthanized 12 when it became clear they could not survive, and the remaining four were released, though the Vet College continues to treat new cases. Dogs that have survived consumed a smaller amount of the food than dogs that died, Center said.
“Some dogs were stealing food from the kitchen counter. Others just stopped eating the food and begged for treats. Unfortunately, some owners used gravy and other mixers to entice their dogs to consume what they thought was safe, quality dog food.”
“Many dog owners I’ve talked to feel responsible for poisoning their beloved dogs,” said Bischoff. Although only about two dozen animal deaths have been officially linked to the tainted pet food, Center and Bischoff know that many more have died or become ill from the tainted food, based on their many communications with veterinarians as far south as Florida.
“Every day, we’re hearing reports from veterinarians in the East and Southeast who have treated dogs that have died from liver damage this past month or so,” said Center. “We’re also concerned about the long-term health of dogs that survive as well as dogs that have eaten the tainted food but show no clinical signs.”
She suspects that surviving dogs may develop chronic liver disease, perhaps liver cancer, and that many dogs that ate the tainted food appear healthy are nevertheless victims of liver damage.
Yet many dog and kennel owners remain unaware that some 19 brands of Diamond, Country Value and Professional dog foods have been recalled.
Screening ill dogs
Early signs that a dog has been poisoned by aflatoxin include lethargy, loss of appetite and vomiting, and, later, orange-colored urine and jaundice (a yellowing of the eyes, gums and nonpigmented skin that reflects substantial liver injury). Severely affected dogs produce a blood-tinged vomit and bloody or blackened stools.
“Since dogs can take several days to three weeks to exhibit serious signs of illness, all animals that consumed recalled lots of food should be examined by a veterinarian as early as possible,” Center said. “Physical exams and blood tests are necessary to differentiate dogs that have been poisoned from those that have not. Unfortunately, the latent onset of signs may require that an individual dog be evaluated several times.”
Cornell veterinarians have verified diagnostic tests enabling the detection of seriously poisoned dogs. Aflatoxin curtails the production of cholesterol and many proteins that profoundly affect blood clotting. A minimum screening profile should assess the liver enzyme ALT to detect damage to the liver, serum cholesterol, total bilirubin concentration and the activity of the anticoagulant proteins antithrombin III (ATIII) and protein C. The coagulation protein tests, which have been adapted for dogs by Cornell researchers, have high value in detecting affected dogs but require collection of a special blood sample (citrated plasma sample) and an assessment by Cornell’s Animal Health Diagnostic Center.
Any dog suspected of aflatoxin poisoning should also have a liver specimen sent to Cornell to definitively confirm the pathologic changes in the liver unique for aflatoxin toxicosis, such as fatty degeneration of individual cells.
“Even if dogs show no signs of illness, if they have eaten the affected food, they should have blood tests submitted to detect liver injury,” Center stressed. “Dogs that show positive results on any of the above tests should be prescribed liver protectants for two months.” For more details, veterinarians should check the Cornell Vet College Web site.
Owners also should take cats that might have eaten contaminated dog food to a vet. Two cats that may have eaten the tainted dog food have died, but no cause of death was determined.
To send dog food to Cornell for aflatoxin testing, veterinarians should send a two-pound sample comprising about five handfuls of food pulled from different parts of the bag. If the food is negative, that does not rule out aflatoxin exposure, Bischoff stressed, because it may take days or weeks for dogs to become ill, and the contaminated food may be long gone. The toxin may also be unevenly dispersed through the food. However, only a liver biopsy can definitively determine the cause of death. Center requests that livers from dogs that have died recently from liver damage or suspected food poisoning be sent to Cornell for evaluation of pathologic changes. Veterinarians should check the Vet College Web site for information on sample submission.
The Cornell veterinarians also recommend that any suspected food be labeled as poison and stored away from animals and children. Save labels with lot numbers from bags. Until further information emerges, if the food was stored in a wooden container, the container should be destroyed. Plastic and metal containers should be sanitized with bleach.
To report animals that might have died recently from the food poisoning, send an e-mail to firstname.lastname@example.org, and the researchers will follow-up with a questionnaire.
Source: Cornell University
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