Aflatoxicosis: Its Effect, Prevention In Animals, Birds And Zoonotic Potency To Human Beings
ABSTRACT
Aflatoxins are toxic metabolites produced by certain fungi in foods and feeds. They are probably the best known and most intensively researched mycotoxins in the world. Aflatoxins have been associated with various diseases, such as aflatoxicosis, in livestock, domestic animals, birds and humans throughout the world. The occurrence of aflatoxins is influenced by certain environmental factors. 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. The clinical signs are often non-specific, and chronicity is often the rule. The practicing food animal veterinarian should always associate non-specific hepatic clinical signs with a possibility of mycotoxicosis, and correlate agricultural practices and feed evaluation with the animal status. Good quality food and resistant strain of animals can lead to greater production and more profit for the poultry, dairy farming.
KEY WORDS: Aflatoxins, Livestock, Pathogenesis, Zoonotic importance, Prevention
INTRODUCTION
Aflatoxicosis is a global concern that affects not only animals and birds but also poses significant risks to human health due to zoonotic potential. Aflatoxins, produced by molds, particularly Aspergillus flavus and Aspergillus parasiticus, are highly toxic compounds that can contaminate a wide range of food and feed products. In this comprehensive article, we will explore the effects of aflatoxicosis on animals, birds, and its potential transmission to humans. Furthermore, we will discuss prevention strategies and the importance of monitoring and regulating aflatoxin levels in the food supply chain.
Aflatoxicosis is a disease caused by the consumption of aflatoxins. Aflatoxicosis occurs in many parts of the world and affects growing poultry especially ducklings and turkey poults, young pigs, pregnant sows, calves, and dogs. Adult cattle, sheep, and goats are relatively resistant to the acute form of the disease but are susceptible if toxic diets are fed over long periods.
CAUSES
Aflatoxins are secondary fungal metabolites produced during metabolism of carbohydrates, fats, proteins, minerals and vitamins. Aflatoxin contamination is typically found in grains and tree nuts, peanuts and peanut products, cottonseed (Fig. 1), corn (Fig. 2) and corn products, groundnut and milk. These toxins are produced by fungi like Aspergillus flavus and Aspergillus parasiticus.The most common aflatoxins are B1, B2, G1 and G2. Aflatoxin B1 is the most potent mycotoxin. Aflatoxin B1 increases the apparent protein requirement of animal and is a potent cancer causing agent. When significant amounts of aflatoxin B1 are consumed, the metabolite M1 appears in the milk within 12 hours.
SOURCES
Contaminated grains and grain by-products are the most common sources of aflatoxins. Corn silage may also be a source of aflatoxins, because the ensiling process does not destroy the toxins already present in silage.
FAVORABLE CONDITIONS FOR AFLATOXIN BIOSYNTHESIS PRODUCTION
The formation of aflatoxins is influenced by physical, chemical and biological factors. The physical factors include temperature and moisture. The chemical factors include the composition of the air and the nature of the substrate. Biological factors are those associated with the host species. Specific nutrients, such as minerals (especially zinc), vitamins, fatty acids, amino acids and energy source are required for aflatoxin formation. Large yield of aflatoxins are associated with high carbohydrate concentrations, such as wheat rice and to a lesser extent in oilseeds such as cottonseed, soyabean and peanuts. The limiting temperatures for the production of aflatoxins are reported as 12 to 41°C, with optimum production occurring between 25 and 32°C. Synthesis of aflatoxins in feeds are increased at temperatures above 27°C, humidity levels greater than 62% and moisture levels in the feed above 14%.
Understanding Aflatoxicosis
Aflatoxicosis is the clinical condition that results from exposure to aflatoxins. These mycotoxins are secondary metabolites produced by certain molds and are characterized by their potent carcinogenic, mutagenic, teratogenic, and immunosuppressive properties. The most prominent types of aflatoxins are B1, B2, G1, and G2, with aflatoxin B1 being the most toxic and carcinogenic.
Effects of Aflatoxicosis in Animals
- Acute Aflatoxicosis
Acute aflatoxicosis is characterized by sudden and severe aflatoxin exposure, leading to rapid clinical signs and high mortality rates. The symptoms include:
- Lethargy
- Reduced feed intake
- Severe liver damage
- Hemorrhaging
- Jaundice
- Coma
- Death
Animals affected by acute aflatoxicosis may die within days of exposure. This form of the disease is less common but highly lethal.
- Chronic Aflatoxicosis
Chronic aflatoxicosis occurs due to prolonged exposure to lower levels of aflatoxins. The effects of chronic exposure are insidious and can lead to various health issues, including:
- Reduced growth rates
- Immunosuppression
- Liver damage and fibrosis
- Increased susceptibility to other diseases
- Decreased reproductive performance
- Lower milk and egg production in dairy and poultry animals, respectively
Chronic aflatoxicosis may lead to poor overall animal welfare and significant economic losses in the livestock and poultry industries.
Effects of Aflatoxicosis in Birds
Aflatoxicosis in birds is particularly common in domestic fowl, such as chickens, ducks, and turkeys. The effects of aflatoxicosis in birds mirror those seen in animals:
- Reduced Growth and Weight Gain
Aflatoxin-contaminated feed can result in slower growth and reduced weight gain in birds, which can be economically detrimental in the poultry industry.
- Egg Production and Quality
Layers consuming aflatoxin-contaminated feed may experience decreased egg production and poor egg quality. Eggs may have thin shells, abnormal shapes, and reduced hatchability.
- Immunosuppression
Aflatoxicosis can impair the immune system of birds, making them more susceptible to various diseases. This poses a significant challenge to the poultry industry, as it may necessitate increased antibiotic use to prevent disease outbreaks.
- Liver Damage
Aflatoxins primarily affect the liver, leading to hepatotoxicity in birds. This can result in fatty liver syndrome and fibrosis, further compromising bird health.
Aflatoxicosis and Human Health: Zoonotic Potency
The most alarming aspect of aflatoxins is their potential to enter the human food chain through contaminated animal products. Aflatoxin-contaminated feed can lead to the presence of aflatoxin residues in meat, milk, and eggs, which can subsequently be ingested by humans. Aflatoxins have been classified as Group 1 carcinogens by the International Agency for Research on Cancer (IARC), indicating that they are carcinogenic to humans.
The health risks associated with aflatoxins in the human diet include:
- Liver Cancer
Chronic exposure to aflatoxins is strongly associated with an increased risk of developing hepatocellular carcinoma, a primary liver cancer. High rates of liver cancer are observed in regions with high levels of aflatoxin contamination in staple foods, such as maize, peanuts, and other crops.
- Immunosuppression
Aflatoxins can weaken the immune system, making individuals more susceptible to infections and diseases. This can have profound health implications, especially in areas where malnutrition and infectious diseases are already prevalent.
- Acute Poisoning
Although rare, acute aflatoxicosis in humans can occur when individuals consume highly contaminated foods. Symptoms of acute aflatoxicosis include vomiting, abdominal pain, jaundice, and even death in severe cases.
Preventing Aflatoxicosis in Animals and Birds
Preventing aflatoxicosis in animals and birds is essential not only to protect animal health and welfare but also to safeguard human health by minimizing the presence of aflatoxins in the food supply chain. Effective prevention strategies include:
- Quality Control in Feed Production
Implement strict quality control measures in the production of animal and bird feeds to minimize the risk of aflatoxin contamination. This includes monitoring the quality of feed ingredients and regularly testing feed for aflatoxin levels.
- Proper Storage Conditions
Aflatoxins thrive in warm and humid conditions, making proper storage of feed ingredients crucial. Ensure that feed ingredients are stored in cool, dry places to minimize mold growth and aflatoxin production.
- Mycotoxin Binders
The use of mycotoxin binders or adsorbents in animal feed can help mitigate the impact of aflatoxins. These additives can bind to aflatoxins and prevent their absorption in the digestive tract, reducing their harmful effects.
- Regular Monitoring and Testing
Regularly monitor and test feed ingredients and finished feeds for aflatoxin contamination. Rapid and accurate testing methods can help identify and mitigate contamination issues before they escalate.
- Strict Regulatory Standards
Implement and enforce strict regulatory standards for acceptable levels of aflatoxins in feed and food products. These standards can help ensure safe food production and protect both animal and human health.
- Education and Training
Educate farmers, feed manufacturers, and other stakeholders in the livestock and poultry industries about the risks associated with aflatoxins and best practices for prevention. Training programs can help disseminate knowledge and encourage responsible feed handling.
- Crop Management
In agriculture, practices such as crop rotation, proper irrigation, and pest control can reduce the risk of mold infestations and subsequent aflatoxin contamination in crops like maize, peanuts, and cottonseed.
Global Efforts and Challenges
The global effort to combat aflatoxicosis is a multifaceted challenge. Several countries have established regulations to limit aflatoxin contamination in food and feed products. These regulations often include maximum allowable levels for aflatoxins in various commodities.
International organizations, such as the World Health Organization (WHO) and the Food and Agriculture Organization (FAO), provide guidelines and recommendations for monitoring and managing aflatoxin contamination.
Challenges in addressing aflatoxicosis include:
- Limited Resources
Many developing countries lack the resources and infrastructure needed to effectively monitor and regulate aflatoxin contamination. This can result in the continued presence of aflatoxins in the food supply chain.
- Climate Change
Changing climate conditions can influence the growth and spread of molds that produce aflatoxins, making it even more critical to implement adaptive strategies in agriculture and food production.
- Lack of Awareness
In some regions, there is a lack of awareness among farmers, consumers, and even policymakers regarding the health risks associated with aflatoxins. Increased education and awareness campaigns are essential.
- Variability in Aflatoxin Levels
Aflatoxin contamination levels can vary significantly from year to year, depending on weather conditions, crop type, and storage practices. This variability makes consistent monitoring and prevention challenging.
Effects of Aflatoxins:
Immunosuppression Carcinogenicity Anaemia Hepatotoxicity Nephrotoxicity Infertility and Abortions Delayed onset of egg production in layers Loss of egg production in layers Loss of appetite, poor egg shell quality and paralysis in birds Poor weight gain in birds (Fig. 3) Ataxia, epistaxis, reduced milk yield, reduced feed efficiency PATHOGENESIS As the dosage and exposure increase, fatty retention by hepatocytes leads to multifocal lesions of lipid-laden hepatocytes, with cellhypertrophy of medium sized biliary ducts.With the loss of centrilobular hepatocytes, a new vascular plexus develops around the central vein, leading to scattered necrosis (Fig. 4) of individual hepatocytes or coalescing into multifocal infarcts. With severe chronic aflatoxicosis, hepatic lesions consist of fibrosis, necrosis, focal lipid accumulation with disseminated fatty degeneration, and atypical hepatocytes. Other lesions are nephrotoxic lesions, immunosuppression, and carcinogenicity. Chronic, subacute aflatoxicosis may cause pyknosis and dilation of the distal convoluted tubular epithelial cells in the kidney. With an increase in dose to acute toxicity, the renal tubular epithelial cells will exhibit necrosis and may be filled with bile pigments, hyaline, and lipid. Immunosuppression is observed in animals fed aflatoxin, but the pathogenesis is not completely understood. Aflatoxin appears to decrease the lymphocyte response to mitogens, inhibit macrophage migration, and decrease the effectiveness of humoral mediators such as complement and cause immunosuppression.
MACROSCOPIC LESIONS
Pale or slightly icteric visible mucous membrane Pale, enlarged and firm liver (Fig. 5) Necrotic foci in liver Petechiae in gastro intestinal trac .
MICROSCOPIC LESIONS
In early stages, the hepatic cells are loaded with fat (Fig. 6). Subsequently centrilobular necrosis sets in. The fibrous tissue proliferates and invading the parenchyma isolates the surviving hepatic cells into small groups of two or more cells or into cell cords having either single or double rows of cells. This appearance is characteristics of pericellular cirrhosis. There is marked bile duct proliferation. Fibrosis causes occlusion of the central veins and so the name Veno occlusive disease. The hepatic cells show intense fatty changes.
HEMATOLOGICAL AND BIOCHEMICAL ALTERATIONS
Aflatoxin causes hematopoietic suppression and anemia observed as decrease in total erythrocytes, packed-cell volume and hemoglobin. Total leucocyte counts are increased and differential leucocytic counts vary with concurrent lymphopenia, monocytosis and heterophilia. Aflatoxin is known to produce hemolytic anemia by decreasing the circulating mature erythrocytes. Lysis of erythrocytes will result in above the normal levels of cellular debris in circulation and consequently the spleen appear congested because of an unusually high concentration of inorganic iron and debris from the circulation. Several biochemical parameters are affected by aflatoxin exposure. Aflatoxin decreases total serum proteins, alpha, beta and gamma globulins, with IgG being more sensitive than IgM. Total serum proteins contents are depressed due to reduced values of alpha and beta globulins and albumin, while gamma globulins are affected more variably. Serum lipoproteins, cholesterol, triglycerides, uric acid and calcium are also decreased.
DIAGNOSIS
Aflatoxin can be detected in milking cows from milk samples. However, diagnosis in non-lactating cattle is more difficult because of the variation in clinical signs, gross pathology, and presence of secondary infection due to immunosuppression. Proper analysis of feed for aflatoxin and other mycotoxin can be a useful tool. The usual method of detection of aflatoxins is thin-layer chromatography and also possibly cytotoxicity tests for those samples not demonstrated by conventional means. A quick screening test for aflatoxin level in shelled corn or ground feed is the Woods’ light test. A black light is held over the sample and fluorescing of a metabolite in the production of aflatoxin might be observed. This is only a screening test, subjective errors and false negatives are quite common.
TREATMENT
Aflatoxicosis is typically a herd rather than an individual animal problem. If aflatoxin is suspected, analyze the ration immediately. Eliminate the source at once, if aflatoxins are present. If aflatoxins are present, the source should be eliminated immediately. Levels of protein in the ration and vitamins A, D, E, K and B should be increased as the toxin binds vitamins and affects protein synthesis. Practice good management to alleviate stress, reducing the risk of secondary infections. Provide immediate attention and treatment for secondary infections.
PREVENTION
Raw materials of feed can be tested for detecting aflatoxins level. This will help to classify the samples for rejection or acceptance. Check the quality of finished feeds with standards. Mold inhibitors, blend of toxin-binders and mycotoxin neutralizing enzymes can be used in production of finished feed. To avoid contamination of milk, lactating dairy cattle should not receive more than 20 ppb in the total ration. Calves should not receive milk from cows fed in excess of 20 ppb, because they can ingest aflatoxin from the milk. Beef cattle can tolerate slightly higher levels of aflatoxin, but yearlings and mature cows should not receive more than 400 ppb in the total ration. Weanlings should not receive more than 100 ppb in their total daily ration. Aflatoxin levels which are considered safe in animal feedstuffs are 20 ppb or lower. Feed contaminated with aflatoxin at a level greater than 20 ppb is not to be sold. Many attempts have been made to detoxify feed but none proven to be totally feasible. Some methods include physical separation, milling, heat, biological inactivation with microorganisms, and chemical treatments. Ammoniation reduces aflatoxin contamination in grain but is not currently approved by the FDA for use in food animals because of uncertainity about byproducts produced. Numerous anticaking agents are available to sequester or bind aflatoxins and reduce absorption from the gastro intestinal tract. One effective binder for aflatoxins is hydrated sodium calcium aluminosilicates, which reduces the effect of aflatoxin when fed to animals at 10 lb/ton. They also provide substantial protection against dietary aflatoxin. This reduces aflatoxin M1 in milk by approximately 50% but do not eliminate residues of aflatoxin M1 in milk from dairy cows fed aflatoxin B1. Other absorbents such as sodium bentonites, polymeric glucomannans have shown variable but partial efficacy in reducing low-level aflatoxin residues in poultry and dairy cattle. To date, the FDA has not licensed any product for use as a mycotoxin binder in animal feeds.
CONTROL
If any mortality, after complete collection of history of particular case, post mortem examination can be carried out to evaluate the cause of the death and also to control the spreading of disease to other animals or birds. Analyze the feed formulation for aflatoxin content. If aflatoxin level is high in finished feed, withdraw and discard those feeds. Educate the farmers on the need to ensure proper drying of products to prevent aflatoxin contamination.
ZOONOTIC POTENCY TO HUMAN
Human health hazards by aflatoxin were mainly due to people eating aflatoxin contaminated food and milk. Direct ingestion of aflatoxins (mainly B1) in contaminated foods of plant origin such as maize nuts and their products had an influence on humans and livestock. Ingestion of aflatoxins carried over from feed into milk and milk products including cheese and powdered milk, where they appear mainly as aflatoxin M1. In addition to the carryover into milk, residues of aflatoxins may be present in the tissues of animals that consume contaminated feed. Aflatoxin residues have been found in animal tissues, eggs and poultry following the experimental ingestion of aflatoxincontaminated feed. Contamination of milk, egg and meat can result from animal consumption of mycotoxin contaminated feed. Aflatoxins, ochratoxin and some trichothecences have been given considerable attention, because they are either carcinogenic or economic concern in animal health. The expression of aflatoxin related diseases in humans may be influenced by factors such as age, sex, nutritional status, and concurrent exposure to other causative agents such as viral hepatitis or parasite infestation.
CONCLUSION
Aflatoxicosis is a significant concern for animal health, food safety, and human health. The effects of aflatoxins on animals, birds, and their potential to enter the human food chain underscore the importance of comprehensive prevention and monitoring strategies. Strict regulations, quality control measures, and education are crucial in addressing this global challenge. By working together to combat aflatoxicosis, we can protect both animal and human health, and ultimately reduce the burden of this toxic threat on societies worldwide.The effect of mycotoxins on food producing animals has only recently been realized. Economic impact has only been speculated, but may be significant. The clinical signs are often non-specific, and chronicity is often the rule. The practicing food animal veterinarian should always associate non-specific hepatic clinical signs with a possibility of mycotoxicosis, and correlate agricultural practices and feed evaluation with the animal status. Good quality food and resistant strain of animals can lead to greater production and more profit for the poultry, dairy farming.
Compiled & Shared by- This paper is a compilation of groupwork provided by the
Team, LITD (Livestock Institute of Training & Development)
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Reference-On Request.
