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Disease Name
[edit]------ Mycotoxins in pet food
Organism
[edit]Mycotoxins are produced as secondary metabolites by fungi most commonly as molds and some yeast in foods and grain. Molds are a very large and diverse group with many different species. These organisms are very hazardous because of their ability to sustain life through different types of environment and temperatures. Molds are capable of producing more than one mycotoxin. The majority of molds are obligate aerobes meaning they require the presence of oxygen to live. Though they are obligate aerobes, they can live under harsh conditions and environment which plays a prominent role in allowing them to live on any food at any time. Exposure to mycotoxins is mainly ingestion but could also be inhaled and through skin. The diseases caused by mycotoxins are called mycotoxicoses. Mycotoxins have a number of acute and chronic effects on animals depending on length of exposure and species. The diagnosis of mycotoxicoses has been proven to be difficult due to the all the similarity of symptoms that are caused by many toxics.
The first big outbreak of mycotoxins occurred in 1960’s in England. Thousands of turkey died in a short span of time to a disease known as Turkey X disease. At that time it was thought to be only turkeys that have been infected, when in fact ducklings and pheasants had been affected as well (AFLATOXINS: Occurrence and Health Risks, 2011). The death rate was very high in all the animals which caused great destruction to the poultry farms. After extensive research, it was found that the animals had been infected through their feed more specifically the peanuts in their feed. The cause of the contamination was traced to Aspergillus flavus, a fungus associated with the mycotoxin aflatoxin (AFLATOXINS : Occurrence and Health Risks, 2001). As a result the turkey X disease, there has been great amount of research done on mycotoxins and their effect on human and animal health. Mycotoxins have been linked to having a highly toxic response in humans and animals leading to critical illnesses and death. In animals, mycotoxins are of serious concern because they are mainly found in cereal grains and nuts. Both cereal grains and nuts are frequently used in animal feed for dogs, fish, birds, cats and many other animals. Mycotoxins are a result of secondary metabolites that are produced by fungi. The secondary metabolites are not essential to the fungi’s growth and development. They are often used as a source to out compete other organisms, for protection, food and escape valves. There are five major groups of mycotoxins that are important in relation to the contamination of animal feed they are: aflatoxins, ochratoxins, trichothecenes, zearalenone, and fumonisins. All the major groups have been found in dog, cat, fish, and bird food throughout the world (Boermans and Maxwell, 2007).
Aflatoxin
Aflatoxin is the most potent of all the mycotoxins. It is produced by aspergillus more specifically Aspergillus flavus and sometimes Aspergillus parasitius (Leung, Diaz, Smith 2006). Aflatoxins consist of B1, B2, G1 and G2. They are all natural occurring aflatoxins in a form of chemical compounds. Aflatoxins are more commonly found in nuts and corn and can be found in other foods as well. They can be converted to other more reactive substances within the body making them very potent. Aflatoxins principal target of organ in the body is the liver, causing damage to it. Upon ingestion and absorption of aflatoxin’s the circulatory system carries it to the liver where it is converted to a highly reactive potent epoxide. These epoxides negatively bind to proteins, DNA, RNA and many other important molecules which lead to the necrosis of the liver (Boermans and Maxwell, 2007). B1 form of alfatoxin is the more potent and more prevalent form of the aflatoxins, due to its toxic carcinogenic effect (Boermans and Maxwell, 2007). The binding of B1 causes a mutation in cells which leads to cancer in animals.
Figure 1: Chemical structures of aflatoxin B1, B2, G1 and G2 The up rise in aflatoxins is persuaded by storage methods, high temperatures, high humidity, seasons, and geographical location. Undeveloped countries are more susceptible than developed countries to have contamination of aflatoxins due to lack of money, agricultural practices, sorting and cleaning of grains and nuts. Developed countries have less risk due to more stringent laws and regulations when it comes to feed and agriculture, reducing the risk of alfatoxin contamination. In order to minimize toxicity food should be kept dry because moisture can allow production of mold which can develop into aflatoxin.
Ochratoxins
Ochratoxin is produced by Penicillum and Aspergillus. There are four forms of ochratoxins A, B, C, D (Leung, Diaz, Smith 2006). Ochratoxin A is known to be the more common and ochratoxin C the most potent. They are primarily found in animal products, grains and cereals. Ochratoxin is a fat soluble and slowly gets excreted from body; therefore it accumulates in the fat of the animals. Ochratoxin mainly accumulates in the kidneys affecting mainly the kidney in the body (Leung, Diaz, Smith 2006). Upon digestion of ochratoxin it enters into the circulatory system where accumulation occurs due to the binding of serum proteins, it inhibits the synthesis of proteins and other functions (Boermans and Leung 2007). Liver damage can also occur with high levels of ochratoxin. Ochratoxin are also known to be carcinogen in mice and rats.
Figure 2: Chemical Structure of Ochratoxin A Ochratoxin A is the most prevalent of all forms mainly formed by Aspergillus ochraceus and Penicillium verrucosum (Richard 2007). It is known to stimulate renal tumors by binding with DNA molecules. Ochratoxin A is a natural occurring contaminate in many foods like coffee beans, fish wine, poultry eggs, and milk.
Trichothecenes
Trichothecenes is comprised of a large number mycotxins with the same basic structure. Over 100 of of trichothecenes have been identified (Boermans and Maxwell, 2007). Four of the main trichothecenes found in animal feed are deoxynivalenol (DON), nivalenol, diacetoxyscirpenol (DAS) and T-2 toxin (Boermans and Maxwell, 2007). Though all four classes are harmful to animal health the most important is deoxynuvalenol (DON) in feed of animals and economic loss agriculture worldwide. Most of the trichothecenes have been found in oats, barley, rice, corn and other crops. All trichothecenes contain an epoxide which is responsible for their toxic effect. The epoxide plays a role in inhibition of DNA and protein synthesis (Richard 2007). Trichothecenes eventually lead to cell death in body due their toxicity levels. They affect dividing cells in the skin, lymphoid, gastrointestinal tract and erythroid cells (Boermans and Maxwell, 2007). They can lower the immune system by decreasing antibody levels and immunoglobulin
.
Figure 3: Chemical structure of Trichothecenes
The contamination of trichochenes is the highest in high temperatures and humidity. Ways to minimize trichochenes is by using insect control and having ample storage with low moisture. Trichochenes brings about a variety of symptoms in animals. Common signs of disease are loss of appetite resulting in weight loss, vomiting, bloody diarrhea, mouth lesions, decrease production of milk or eggs, immune suppression and gastrointestinal hemorrhage (Richard 2007). Zearalenone Zearalenone is naturally produced by the fungus Fusarium graminearum. It is known for its estrogenic effects in farm animals like sheep, pigs and cattle (Zain 2011). These effects are attributed to their chemical structure and are produced primarily by fusarium. Zearalenone is a phenolic resorcyclic acid lactone chemical that when consumed by animal’s is estrogenic (Richard, 2007). It is found in crops such as cereal, barley, wheat, but most often found in corn. The production of fusarium occurs in moist cool temperatures all over the world. The adequate storage of food helps to minimize the onset of zearalenone. Zearalenone causes reproduction problems in animals depending on amount of mycotoxin contamination. Animals may have problems with development of fetus, ovulation, conception, and capability of newborn. Zearalenone binds in the target cells to cytosolic estoren receptors due to chemical similarities to estrogen (Boermans and Maxwell, 2007). The most often signs of zearalenone contamination is due to the over stimulation of estrogen-dependent tissues. Dogs are affected by zearalenone which lead to pyometra which is an infection in the uterus (Boermans and Maxwell, 2007).
Fumonisins
Fumonisins are toxins that are produced by Fusarium verticillioides and F. proliferatum. Through research it has been shown that wet and warm weather seem to influence the production of this mycotoxin. There have been found to be 15 different forms of fumonisins with B1, B2, B3, B4, A1 and A2 being the main ones. Fumonisins B1, B2, B3 are the most common. B1 has been shown to be the most toxic with seventy percent of all cases (Boermans and Maxwell, 2007). Fumonisins have long hydrocarbon chains similar to sphingosine and sphinganine the carbon chain is what gives it its toxic effect on animals. These mycotoxins are readily absorbed from stomach, microflora in the stomach can inactivate them. Upon entering the blood it can damage many organs in animals. Due to the similarity of fumonisins and sphingosine and sphinganine and their bases it prevents the activity of ceramide synthase to produce sphingolipids (Boermans and Maxwell, 2007). The interruption of these lipids causes damage to cell and promotes cell death. Fumonisins also affects the cardiovascular system negatively. The organs most affected by this mycotoxin are the kidney and liver, chronic levels of fumonisin affect the immune system. Horses have been found to be affected severely by fumonisins, it softens the white matter in brain which is called leukoencephalomalacia (John, 2007). It is also known to cause pulmonary edema in pigs and various others health conditions in livestock. Unlike other mycotoxin there is no decrease in the production of milk and eggs and there is little absorption of mycotoxin. Symptoms of contamination differ with animal species and dosage amounts. One key indicator is reduced appetite, weakness, lesions and skeletal abnormalities. In more severe cases like in horses it will lead to blindness and depression.
Fumonisins is mainly found in corn, but other crops have been found to be contaminated like rice. Fumonisins enters the ear and kernels of corn through damaged area caused by insects. This will cause the whole corn to become contaminated as opposed to just exterior. Signs of this would be pink kernel rot on kernals or ears. The highest level of fumonisins occurs in kernals with damage found on them causing severe animal disease. Unlike other mycotoxin the adequate storage of corm does not seem to affect contamination levels. Contamination is increased when corn is stored with kernel damage, or broken kernel.
Symptoms
[edit]In general symptoms of mycotoxin exposure vary due to many different forms of secondary metabolites produced from fungi. Symptoms are affected and vary depending on species of animals, length of exposure and the amount of mycotoxin exposed too. There are Mycotoxins have four basic levels of disease: acute, chronic, mutagenic, and tetragenic (Piit, 2000). The most common symptoms found in acute toxicity is the breakdown of liver and kidney with more serious cases leading to death. Low levels of mycotoxins affect in the long term they can lead to cancer and mutations in DNA synthesis. Mycotoxin toxicity can affect many different organs and systems in the animals including liver, kidney, brain, pulmonary system, cardiovascular system, and central nervous system. Some mycotoxins are carcinogenic and can suppress the animal’s immune system making them more susceptible to other infections.
Treatment
[edit]Mycotoxins are very diverse chemically thus making hard to control. Since the discovery of mycotoxins there have been numerous different strategies to control fungi growth. Biological control is used as a atoxigenic control for fungi in order to out compete other fungi that are similar (Zain, 2007). The effectiveness of bio-control involves identifying location, organism, condition and temperature that it grows in to effectively control the mycotoxin growth in order to reduce risk. Chemical control is used on crops to control fungal growth, mycotoxin production and insect damage to crops. Today the pesticides are being more regulated due to concern for the environment and various food safety in animals. Decontamination in animals is a way of treating toxicity in feed. Decontamination can be done through chemoprotection or enterosorption (Zain, 2007). Chemoprotein is done through a variety of chemicals compounds as well as food combinations like broccoli. Certain foods prevent the conversion of mycotoxin to epoxide, the highly reactive toxic that is made from some mycotoxins. Chemoprotein is used to increase an animal’s detoxification process upon being contaminated. Another method to decontaminate animals is by using absorption substances, oil and various water extracts.
Guidelines
[edit]Below are some guidelines set by FDA as to the levels acceptable in animals feed with mycotoxin in their feed. The guidelines are to give the levels acceptable safe to animals, but mycotoxins affect different animals in different ways.