Aflatoxin Occurrence, Detection, and Novel Strategies to Reduce Toxicity in Poultry Species

*Surya Kanta Mishra and Bijaya Kumar Swain*

### **Abstract**

Aflatoxins (AF) are the commonly occurring mycotoxins produced by various *Aspergillus* species including *A. flavus, A. parasiticus*, and *A. nominus*. As secondary metabolites of these fungi, AF may contaminate a variety of food and feedstuffs, especially corn, peanuts, and cottonseed. Among the many known AFs, AFB1 is the most commonly encountered and the most toxic. In poultry, adverse effects of AF include reduction in growth rate and feed efficiency, decreased egg production and hatchability along with increased susceptibility to diseases, besides residues in food chains. Many rapid screening methods for detecting aflatoxin are available currently, namely: thin layer chromatography (TLC), HPTLC, HPLC, enzyme-linked immunosorbent assay (ELISA), monoclonal antibody kits, and affinity column chromatography, making the detection of AF precise. For field application, rapid assay kits, e.g., Aflatest of Vicam and Afla-2-cup of Romers Labs, are currently available. The most novel ways to counteract aflatoxin already accumulated in the feed could be by getting them bound to inert compounds before absorption from host's intestine. Among various classes of poultry, ducks followed by turkeys form the two most vulnerable poultry species, among others. Considering the inherently high genetic variation between duck breeds for AFB susceptibility, a genetic selection program to improve AFB resistance can be a long-term option. Further epigenetic sensitization of the AFB-susceptible poultries through mild AFB exposures is getting reported as an emerging genetic approach to counter AFB susceptibilities. The chapter discusses most of these, in greater detail.

**Keywords:** aflatoxin, detection method, occurrence, detoxification, poultry, susceptibility

## **1. Introduction**

An outbreak of Turkey-X disease in the United Kingdom in 1960s following the ingestion of poultry feed containing Brazilian ground nut cake led to the discovery of a group of compounds, which are now known as aflatoxins (AFs). Chemical and microbiological investigations soon revealed that the toxic effects produced by Brazilian ground nut cake had resulted from the presence of four secondary metabolites of the mold *Aspergillus flavus* in the diet [1].

Aflatoxins (AFs) are difuranocoumarins mainly produced by two *Aspergillous* species, namely *Aspergillous flavus* and *Aspergillousparasiticus* [2]. According to their chemical structures, there are two main categories of AFs; the first category being difuranocoumaro-cyclopetene group and includes aflatoxins B1, B2 (AFB1, AFB2) while the second category is formed by the AFG1 and AFG2. The nomenclature of AFB1 and AFB2 is derived from the blue fluorescent color produced and visualized under UV light while AFG1 and AFG2 produce green fluorescent color [3, 4]. Among all the discovered mycotoxins, aflatoxins form the most elaborately researched group, because of their toxicological and hepatocarcinogenic effect in various susceptible animals. The toxigenicity among four AF compounds has been rated in order such as: B1 > B2 > G1 > G2. Chemically, AFs are polycyclic unsaturated compounds consisting of a coumarin nucleus flanked by a highly reactive bifuran system on one side and either a pentanone or a six member lactone on the other side. The toxic nature of AFs is due to its chemical structure. The lactone ring undergoes epoxidation to produce AFB1 2-3 epoxide, which accounts for its toxic properties. Any alteration in opening of lactone ring or saturation of double bond associated with lactone ring causes reduction in the toxicity [5]. Consumption of AF contaminated agricultural stuffs thus becomes the main route of exposure in poultry. Major adverse effects of AFs are loss of appetite, decreased feed intake, poor feed utilization, immunosuppresion, decreased egg production, and increased mortality in poultry [6–8] and additionally, the suppression of immune system [9, 10]. Immunosuppressive, hepatotoxic haemorrhage [11], carcinogenic, mutagenic, growth inhibitory [12], and teratogenic [13] effects can be detected according to animal species, sex, age and aflatoxin type, exposure dose and period. The median lethal dose (LD50) of AFB1 is estimated to be between 0.3 and 18 mg/kg according to the route of administration, species of animal, age, sex, and health condition. Poultry are usually more susceptible to AFs than mammals. Within poultry, ducks are most susceptible species of all, followed by the turkey poults and thereafter, the chickens. Young animals are more susceptible to AFs than matured animals. Nutritional deficiencies, especially protein and vitamin E, increase the susceptibility to AFs [14]. Decrease in nutrient absorption in broilers fed AFB1-contaminated diet is because of the effect of toxin on systemic metabolism and not an effect on digestive functionality [15, 16].

Physical, chemical, and biological methods are essential to counteract the levels of contamination of AF, already accumulated, in foods and feeds. The cost involved and reduction in nutritive value of feed are some of the constraints that limit the use of such procedures during the feed preparation. Various studies indicate that it is practically not possible to totally eliminate the molds and their toxins from the feed. Therefore, there is need to use suitable agents that are capable of binding the toxins selectively in the gut, thus limiting their bioavailability to the consumer. Further, presence of toxic residues in poultry products (egg, meat), which enters in to the food chain, may pose potential risk by their hazardous effects on the health of human beings [17]. An approach to the aflatoxin contamination problem has been to use non-nutritive and inert adsorbents in the diet to bind AF and reduce the absorption of AF from the gastrointestinal tract. Use of adsorbents such as zeolites and alluminosillicates has proven successful, but their possible interaction with feed nutrients is a cause of concern [18, 19]. Therefore, the occurrence of AF, its detection procedures in different feedstuffs and different strategies to ameliorate its effect on the performance of poultry, and the reduction of their residues in food for food safety are discussed in detail below.

*Aflatoxin Occurrence, Detection, and Novel Strategies to Reduce Toxicity in Poultry Species DOI: http://dx.doi.org/10.5772/intechopen.107438*

### **2. Occurrence**

Aflatoxins were first identified in early 1960s and since then have been the most studied mycotoxins. Aflatoxins (AFs) are the most commonly occurring mycotoxins that are heterocyclic compounds produced as secondary metabolites mainly by various *Aspergillus* species including *A. flavus, A.parasiticus,* and *A. nominus* [20]. The biosynthesis of AFs consists of 18 enzymatic steps with at least 25 genes responsible for producing the enzymes and regulating the biosynthetic process [21, 22]. These mycotoxins are mainly found in agricultural products in tropical and subtropical regions [23–25]. Almost all agricultural commodities will support the growth of aflatoxin-producing fungi *A. flavus, A. parasiticus*. Formation of AF can occur during the pre and post-harvest stages of food production as long as a suitable environment for mold growth is available. Optimal conditions for AF production are a water activity in excess of 0.85 (85% RH) and a temperature of 27°C, conditions that are frequently encountered in Mediterranean region. Different crops vary in their ability to support fungal colonization because of differences in the chemical composition of each commodity. The incidence and degree of AF contamination vary with seasonal and geographical factors and also with the conditions under which the crop is grown, harvested, stored, and transported [26]. Factors affecting the production and occurrence of mycotoxins in crops and the level of contamination in feed and food entail climatic conditions such as temperature, relative humidity, and agricultural operations such as usage of fungicides. Other factors include: drying, processing, handling, packaging, storage, and transport environment. Insects play an important role in contaminating the agricultural commodities through physical damage of the grains and mechanical transmission of the microorganisms [27–30]. As such, most of the cereal grains, oil seeds, and tree nuts are susceptible to fungal invasion and consequently formations of mycotoxin aflatoxin. Agricultural products such as cereal grains and forages can be polluted during pre-harvest [field period, harvest, and post-harvest (storage and transportation period)]. Maize and other grains used in poultry feed could also be infected by pathogenic molds and thereby produce aflatoxins, even when they may be destroyed at different rates during industrial processing [2, 14, 31, 32]. The fungal species can invade foods and feedstuffs depending upon the geographical and climatic conditions of a particular region. Aflatoxins are mostly expected in tropical areas where climatic conditions and storage practices are favorable to fungal growth and toxin production, whereas other mycotoxins such as ochratoxins and fumonisins are detected in moderate, subtropical and tropical locations, with zearalenone and trichothecenes forming the worldwide mycotoxins [33, 34]. Unfortunately, the food and feed contamination by AFs is a persistent problem worldwide. The outbreaks due to AFs are more prone in tropical and subtropical areas, with a few in temperate regions. Further, the Mediterranean zones have become prone to AFs contamination due to shifting in traditional occurrence areas of AFs because of climate change, namely increase in average temperature, CO2 levels, and rainfall pattern [35]. This has led to an increased occurrence of AFs worldwide, due to increase in contamination of crops.

Aflatoxins are often present in feedstuffs and cause some adverse effects, which can range from: vomiting, weight loss, and acute necrosis of parenchyma cells to various types of carcinoma and immunosuppression in large animals, pets, and poultry birds [36, 37]. Aflatoxin B1 (AFB1), among the four major types of AFs, is the most toxic and potent carcinogen in humans and animals [38]. AFB1 causes series of pathophysiological changes in an organism such as lower growth rate, malnutrition,

silenced immune response, and disturbed gastrointestinal tract. Also, AFB1 can induce various histopathological manifestations of hepatocytes such as proliferation of the bile duct, centrilobular necrosis and fatty degeneration of the hepatocytes, and hematoma [29, 39–41]. AFB1 is already reported to induce hepatocellular carcinoma in many species of animals including fishes (rainbow trout, sock eye salmon, and guppy), poultry (turkeys, ducks, and geese), non-human primates (rhesus, cynomolgus, African green, and squirrel monkeys), and rodents (rats, mice, and tree shrews) [36, 42]. In poultry, AFB1 mainly affects the liver, kidney, immune organs (spleen, bursa of fabricius, and thymus), and gastrointestinal system. Poultry industry, factually, is one of the largest, most organized, fastest-growing, and vibrant segments of agro-industries, generating direct and indirect employment and income for millions of people, in developed and developing countries [43–45]. According to an estimate by the Food and Agriculture Organization (FAO), 25% of the world's food crops are affected by mycotoxins, and the rate of mycotoxin contamination is likely to increase in line with the trend seen in preceding years [46–49]. A worldwide mycotoxin survey in 2013 revealed that 81% of around 3000 grain and feed samples analyzed had at least one mycotoxin, which was way higher than the 10-year average (from 2004 to 2013) of 76%, in a total of 25,944 samples. The most notorious mycotoxins, thus, are aflatoxins (Afs), which often result in low performance in poultry, decreased quality of egg and meat production, and then, cause significant economic losses [50–52]. In broilers, aflatoxins drastically affect almost all valuable production factors including weight gain, feed intake, and feed conversion ratio (FCR) and induce immunosuppression, which is directly related to reduced effectiveness of vaccination programs, increased risk of infectious diseases, and high mortality. In layers, aflatoxins cause the decrease in egg production, egg size, and egg quality.


Included in the text, is a tabular presentation of various feed materials/grains with mention of their aflatoxin contamination ranges along with incidence rates (**Table 1**).


*Aflatoxin Occurrence, Detection, and Novel Strategies to Reduce Toxicity in Poultry Species DOI: http://dx.doi.org/10.5772/intechopen.107438*

#### **Table 1.**

*Surveys of food and agricultural products contaminated with aflatoxin in different locations.*
