Warning: include_once(../article_type.php): failed to open stream: No such file or directory in /home/suxhorbncfos/public_html/jdvs/JDVS.MS.ID.555685.php on line 204
Warning: include_once(): Failed opening '../article_type.php' for inclusion (include_path='.:/opt/alt/php56/usr/share/pear:/opt/alt/php56/usr/share/php') in /home/suxhorbncfos/public_html/jdvs/JDVS.MS.ID.555685.php on line 204
1College of Veterinary Medicine, Mekelle University, Ethiopia
2College of Medical and Health Science, Wollega University, Ethiopia
Submission: February 27, 2018; Published: May 31, 2018
*Corresponding author: Abriham Kebede; School of Veterinary Medicine, College of Medical and Health Science, Wollega University, P.O. Box, 395,
Nekemte, Ethiopia, Tel: +251-917-095-077; Email: email@example.com
How to cite this article: Abebe B, Abriham K, Yobsan T. Review on Aflatoxin and its Impacts on Livestock. Dairy and Vet Sci J. 2018; 6(2): 555685.
Food contamination occurs when something is found in the food that should not be there. The main sources of contaminations are chemicals,
physicals and microorganisms which include bacteria, virus, fungi, yeast and mold. The threat of aflatoxin contamination in food commodities
and its association with health risk in both animals and humans is becoming an increasing concern over years. Aflatoxins are a group of
mycotoxins mainly produced by Aspergillus flavus and Aspergillus parasiticus. These aflatoxins are divided into six major toxins according to
their fluorescent properties under ultraviolet light and their chromatographic mobility. Both A. flavus and A. parasiticus produce aflatoxins B1
and B2 which produce blue fluorescence, while A. parasiticus produces aflatoxins G1 and G2 which have green fluorescence.
The four times hydrated aflatoxinB1and B2 is converted to aflatoxin M1 and M2 respectively. They present in the milk of lactating mammals
which have consumed aflatoxin contaminated feed .Aflatoxin B1 is the most toxic and the most prevalent. There are great qualitative and
quantitative differences in the aflatoxin producing abilities displayed by different isolates of each aflatoxigenic species. Lethal dose (LD50) values
of these toxins range from 0.5 to 10mg/kg according to the considered aflatoxin. It presence in commodities is unavoidable. To avoid their
occurrence in the food chain management strategies requires. Their fore farmers, government agencies, food processors, scientists and others
should be evolved in the system. Network should be done with community and create society awareness to control contamination of aflatoxin.
The contamination of food is worldwide problem. Food
contamination occurs when something is found in the food that
should not be there. The main sources of contaminations are
chemicals, physicals and microorganisms which include bacteria,
virus, fungi, yeast and mold. Fungi are unavoidable remarkable
organisms that produce a wide range of natural product often
called secondary metabolites. Mycotoxins are fungal metabolites
that are currently considered to be the most dangerous and
wide spread contaminant in food and animal feeds. Foodstuffs
can be contaminated with mycotoxins before production, during
storage, processing, transportation or marketing of the food
products. High temperature, moisture content and water activity
are among the predisposing factors that facilitate the production
of mycotoxins in food .
Aflatoxins are a group of mycotoxins mainly produced by
several fungus species in the genus Aspergillus. It includes A.
flavus and A. parasiticus A. pseudotamarii, and A. nomis species.
Among these species A. flavus and A. parasiticus are well known.
These organisms invade crops and grow on foods during storage
if temperature and humidity levels are favorable. The relative
proportions and amounts of the various aflatoxins on food crops
depend on the Aspergillus species present, pest infestation,
growing and storage conditions, and other factors. Although
these species have similar geographical ranges, A. parasiticus is
less widely distributed and A. flavus is the most widely reported
fungus in foodstuffs. Aflatoxins are metabolized in ruminants by
the liver and excreted in the bile. The major aflatoxins produced
in feed stuffs are B1, B2, G1, G2, m1 and m2. Both A. flavus and A.
parasiticus produce aflatoxins B1 and B2, and A. parasiticus also
produces aflatoxins G1 and G2 .
Among these several type of aflatoxin strain, Aflatoxin B1 is
the most potent mycotoxin (toxic substance produced by a mold).
This type of toxin increases the apparent protein requirement of
cattle and is a potent cancer causing agent (carcinogen). When
significant amounts of aflatoxin B1 are consumed, the metabolite
M1 appears in the milk within 12 hours. For all type of aflatoxin
metabolites, the lethal dose (LD50) values range from 0.5 to
10mg/kg according to the considered susceptibility of host. Aflatoxin contamination has been the most common cause of
acute and chronic mycotoxicos is in animals and humans.
Hepatotoxicity, immunosuppression, carcinogenicity and
nephrotoxicity are the major effects of aflatoxins. It has gained
increasing attention due to their harmful effects on human
and animal health and also due to the widespread presence of
aflatoxigenic fungi in all the agricultural commodities under
field and storage conditions . Aflatoxin occurs worldwide. The
recent estimates suggest that there are more than five billion
people worldwide at risk of chronic exposure to aflatoxins.
But it occurs more frequently in tropical countries because of
high temperature, moisture, unseasonal rains. Most of the time
aflatoxicos is a consequence of ingestion of contaminated feed
with aflatoxins. That is continued to be problems of significant
public health concern as long as people consumed contaminated
animal products and considered as public health important.
In the developing world seriously affect people’s health and
livelihoods, as freedom of choice in food is limited for a poor and
food-insecure population [4,5]. Therefore, the objective of this
paper is to highlight aflatoxins and their significance.
Aflatoxins are secondary fungal metabolites included in the
class of mycotoxins. That produced by fungi genus Aspergillus
species of. It produced during their growth under favorable
conditions . That contaminated agricultural commodities and
can cause sickness or death in humans and animals .
There are several different types of aflatoxins strains. The
most common naturally produced are B1, B2, G1, and G2 and
two additional strains, M1 and M2 are the metabolic products of
contaminated food or feed and are found in milk and other dairy
products [8,9]. Aflatoxins designated by B1 and B2 show strong
blue fluorescence under UV light, whereas the G1 and G2 forms
show greenish yellow fluorescence. Aspergillus flavus produces
aflatoxin B1 and B2.Othertoxic compounds produced by A. flavus
are cyclopionic acid, kojic acid, nitropropionic acid, aspenoxin,
aflam and aspergillic acid. A. parasiticus produces aflatoxin
G1and G2 in addition to B1 and B2, but not cyclopionic acid 
Aflatoxins are produced by fungi in the genus Aspergillus that
grow on grains and other agricultural crops. They exist as color
less to pale-yellow crystals at room temperature. They are slightly
soluble in water and hydrocarbons, soluble in methanol, acetone,
and chloroform, and insoluble in non polar solvents. Aflatoxins
are relatively unstable in light and air, particularly in polar
solvents or when exposed to oxidizing agents, ultraviolet light
or solutions with a PHbelow3orabove10. Aflatoxins decompose
at their melting points, which are between 237 °C (G1) and 299
°C (M1), but are not destroyed under normal cooking conditions.
They can be completely destroyed by autoclaving in the presence
of ammonia or by treatment with bleach. Physical and chemical
properties of aflatoxins are listed in the following .
Physical properties of Aflatoxins: Aflatoxins are crystalline
odorless solids when isolated and the color range from pale
white to yellow. The melting points range from 268 °C for B1
down to 190 °C for G2 .
The optimal water activity for growth of A. flavus is high
(about 0.99). The maximum is at least 0.998 whereas the
minimum water activity for growth has not been defined. In
general, production of toxins appears to be favoured by high
water activity. Aspergillus flavus is reported to grow within the
temperature range 10-43 °C. The optimal growth rate occurs
at a little above 30 °C, reaching as much as 25mm per day. The
aflatoxins are produced by A. Flavus over the temperature range
15-37 °C. It is not possible to specify an optimum temperature
for the production of the toxins, although production between
20-30 °C is reported to be significantly greater than at higher and
lower temperature .
Chemical properties of aflatoxins: Aflatoxins belong to
the group of difuranocoumarins. The compounds are usually
soluble in methanol, chloroform, acetone and acetonitrile which
are slightly polar but insoluble in non-polar solvents. Aflatoxins
react with alkaline solutions causing the hydrolysis of the
lactones moiety. This hydrolysis is reversible since it has been
shown that recyclization occurs following acidification of basic
solution containing aflatoxin. At higher temperatures above
1000C, ring opening followed by decarboxylation occurs and
the reaction may proceed further, leading to the loss of methoxy
group from the aromatic ring .
In the presence of mineral acids aflatoxins B1 and G1 are
converted into aflatoxin B2A and G2A, due to acid catalyzed
addition of hydroxyl group across the double bond in the furan
ring. In the presence of acetic anhydride and hydrochloric acid,
the reaction proceeds further to acetoxy derivative. Similar
adducts of aflatoxin B1 and G1 are formed with formic acidthionyl
chloride and trifluroacetic acid. Many oxidizing agents,
including sodium hypochlorite, potassium permanganate,
chlorine, hydrogen peroxide, ozone and sodium per borate, react
with aflatoxin molecule in some way as indicated by the loss of
fluorescence in ultraviolet light at 365nm .
Hydrogenation of aflatoxin B1 and G1 yields aflatoxins B1
and G1 respectively. Further reductions of aflatoxin B1 by three
moles of hydrogen yields tetra hydroxyl aflatoxin. Reduction of
aflatoxin B1 and B2 with sodium boro hydride yields aflatoxin
R-B1 and R-B2 respectively. These arise as a result of opening of
the lactones ring followed by reductions of the acid group and
reduction of the keto group in the cyclopentene ring .
Aflatoxins, like any other mycotoxins, are a subclass of
substances which originated as a result of secondary metabolism
of fungi. Unlike primary metabolites, these secondary metabolites
are not essential for the growth of the fungi but have survival functions in nature. Genes required for aflatoxin production have
persisted in fungi for more than 100 million years. Expression
of secondary metabolite biosynthesis genes does not occur at
high growth rates, which indicates that the synthesis of these
metabolites occurs during growth repression. Aflatoxins induce
DNA damage, negatively affect damage repair, and alter DNA
base compositions of genes. Aflatoxins are associated with both
toxicity and carcinogenicity in human and animal populations
The usual routes for aflatoxins exposure are ingestion of
aflatoxin contaminated foods and feeds . Diet is the major
way through which humans as well as animals are exposed
to aflatoxins. Apart from this, exposure to aflatoxin can be
through ingestion of contaminated milk M1 (metabolite of
AflatoxinB1) . The amount of this metabolite decides
the species susceptibility as this can induce mutations .
Moreover species susceptibility to aflatoxin mainly depends on
its liver detoxification systems, genetic makeup, age and other
nutritional factors .
Wide variations of LD50 values had been obtained in animal
species tested with simple doses of aflatoxins for most species.
The LD50 values ranges from 0.5 to 10mg/kg body weight.
Animal species respond differently in their susceptibility to
chronic and acute toxicity of aflatoxins. In each species the liver
is the primary target of acute injury. Toxicity can be influenced
by environmental factors, level of exposure and duration of
exposure, age, health and nutritional status of diet. Metabolism
plays a major role in determining the toxicity of aflatoxins B1
Studies show that this aflatoxin requires metabolic activation to
exert its carcinogenic effect .
According to the World Health Organization (WHO).
Hepatocellularcarcinoma in human is the third cause of cancer
leading to deaths globally . Aflatoxins metabolized by
enzymes in the liver bind to proteins and causes acute toxicity).
AflatoxinB1 is the most toxic of the aflatoxins and the strongest
naturally occurring chemical liver carcinogen known immunity
and nutritional processes .
Acute aflatoxicosis, associated with extremely high doses of
aflatoxin, is characterized by hemorrhaging, acute liver damage,
edema, and high mortality rates in humans. Acute aflatoxicosis
is also related with sporadic outbreaks of the consumption of
highly contaminated foods. Early symptoms of acute high level
exposure to aflatoxin include diminished appetite, malaise, and
low fever; later symptoms, which include vomiting, abdominal
pain, and hepatitis, can signal potentially fatal liver failure .
Since, the role of the kidney as an organ of excretion
reabsorption and general homeostasis make it the most subjected
one for aflatoxicosis. The load of accumulated toxins within the
tubules enhances mycotoxins nephrotoxicity. This nephrotoxicity
is due to degenerative effects of glomerular basement membrane.
The sever degenerative changes swelling of the cells even rapture
of the membrane and cellular organelles in the tubular lumen as
well as fibrocytic reaction and congestion of the vasculature in
addition to glomerular reaction is manifested by atrophy of both
visceral and paretalshirnked cells .
Dairy and beef cattle are more susceptible to aflatoxicosis
than the other species. Young animals of all species are more
susceptible to the effects of aflatoxins than mature animals.
Pregnant and growing animals are less susceptible than young
animals but more susceptible than nature animals. Toxicity
due to aflatoxins, under natural conditions, is usually sub acute
or chronic, depending on the level of exposure. Occasionally,
acute cases are also seen. In general affected animals show
reduced growth rate, weight loss, immune suppression, icterus,
hemorrhagic enteritis, reduced performance, and ultimately
Aflatoxicosis in milking cows is readily evident from milk
samples. However, diagnosis in nonlactating cattle is more
difficult because of the variation in clinical signs, gross pathology,
and presence of other diseases due to suppression of the immune
system. More than one mold or toxin can further complicate
diagnosis as well. By the time overt symptoms are noticed, the
prognosis is poor. Aflatoxins have usually been detected by their
photo physical properties, such as by absorption and emission
spectra. For instance, aflatoxins show characteristic absorption
at 360 nm, which is the absorption maximum of the aflatoxin
Different methods of detection and quantification
of aflatoxins are: ELISA, electrochemical immune sensors,
chromatography and fluorescence. ELISA is widespread
technique. Competitive direct enzyme linked immune sorbent
assay test is one of the most common tests conducted in immune
biochemistry that allows the user to obtain exact concentration
in parts per billion. But it has the disadvantage of requiring
well equipped laboratories, well trained professional, harmful
solvents and several hours to complete an assay .
The detection and quantification of aflatoxins by using
electrochemical immune sensor has proven to be efficient, easy
to use and able to detect very low levels of aflatoxin. Fluorescence
detection is a very good alternative to the conventional
techniques. It has a very high sensitivity. But it is inexpensive
Rapid detection techniques are optical fiber, electrochemical
transduction, low injection monitoring and biosensors. Most of
these still present a lack of applications because of their practical inconveniences except biosensors. The biosensors have been
designed to overcome the drawbacks that the common tools
employed to detect and quantify aflatoxins presents. Apparently
then measurement of aflatoxins in the future tends to be the
combination of optical, immunochemical and fluorescence
Aflatoxins can affect a wide range of commodities including
cereals, oilseeds, spices, and tree nuts as well as milk, meat,
and dried fruit. Reports from different part of the world
indicated incidence of aflatoxins vary from 40 to 92%. Especially
developing countries located in the tropical regions have greatest
risk. Their climate is favourable to growth of aflatoxin. Where
dietary food stuffs and Staple food source commodities is highly
contaminated with aflatoxins . Aflatoxicosis is the most
important food borne mycotoxins. It has greatest significance in
tropical developing countries [31,32].
Epidemiological studies carried out in several parts of Africa
and Asia indicates a correlation between exposure to aflatoxins
and primary liver cancer . Besides several epidemiologic
investigations is shown that increased aflatoxin ingestion
correlates with increased risk of hepatocellular carcinoma in
Aspergillus flavus and aflatoxin forms sclerotia which
allow it to survive in soil for extended periods of time . The
sclerotia are the principal sources of primary inoculum. They
are also found in foodstuffs and are not destroyed by normal
industrial processing or cooking since they are heat-stable.
Conditions such as high temperatures and moisture, unseasonal
rains during harvest and flash floods lead to fungal proliferation
and production of mycotoxins . Poor harvesting practices,
improper storage and less than optimal conditions during
transportation, marketing and processing can also contribute
fungal growth and increase the risk of mycotoxins production
. Some of their metabolites are still toxic and may be involved
in human diseases. The toxic effects of aflatoxins on organs like
liver, kidney and mainly their carcinogenic effects are mostly
known causes of morbidity and mortality .
The economic consequences of aflatoxicosis are the
major areas of concern. Aflatoxins have negative impact on
human health, animal productivity and trade. Generally, when
susceptible animals are fed contaminated feeds it results
in reduced growth rates, illness, and death; moreover, their
meat and milk may contain toxic biotransformation products.
Livestock owners often take farmers and feed companies to
court legal battles can involve considerable amounts of money
. The direct economic impact of aflatoxin contamination in
crops results mainly from a reduction in marketable by rejection
of products from the international market and losses incurred
from livestock disease, consequential morbidity and mortality
which leads to volume and value loss in the national markets
which is huge economic loss .
Recommended sanitary and phytosanitary standards set for
aflatoxins adversely affect grain trade in developing countries,
specifically in the international market, products that do not
meet the aflatoxin standards are either rejected at the border,
rejected in channels of distribution, assigned a reduced price
The crops contaminated with high levels of aflatoxins are
sometimes diverted to animal feed, which resulting in reduced
growth rates and illness of animals consuming toxic contaminated
feeds. Many countries have established regulations to limit
exposure to aflatoxin, typically expressed in parts per billion
(ppb). These regulations can result in foregone trade revenues
arising from increased cost of meeting the standards including
cost of testing, rejection of shipments and even eventual loss of
admissibility into foreign markets .
Toxigenic fungal pathogens are important constraints to the
production of the crop, affecting the quality of the seeds through
spoilage, however, aflatoxin contamination is the most important
quality problem in Ethiopia with serious health consequences for
human and livestock for example groundnut plays an important
role as a food as well as a cash crop in Ethiopia. Currently the
crop is becoming one of the high value crops that are growing in
the dry land areas of the Tigray region, Northern Ethiopia, but
the groundnut production highly attack by aflatoxicosis .
The human health consequences of acute aflatoxicosis alone
range from death to exacerbated malnutrition, devastating to the
affected populations. When lactating animals are fed aflatoxin
contaminated feed, they excrete aflatoxin metabolites into
the milk. The aflatoxins are capable of causing aflatoxicosis in
consumers of milk. This is why government regulations specify
that milk must be free of aflatoxin. However, action is not taken
until the aflatoxin level exceeds 0.5ppb in market milk, the
level below which there is no hazard for the consuming public.
“Action levels” for livestock represent the level of contamination
at which the feed may be injurious to their health or result in
contamination of milk, meat or eggs .
Aflatoxicosis can be prevented by feeding rations free of
aflatoxin. Preventing aflatoxin contamination requires ongoing
and thorough sampling and testing program. It requires
purchasing feed from reputable persons and companies
experienced in aflatoxin prevention and who have a proven
record of properly monitoring their feed products. A reliable
feed company will also carry insurance to cover misfortunes with aflatoxins or other problems. A good deal on feed prices can
be the most expensive buy a dairy farmer ever makes if it proves
to contain aflatoxin. Storing feed at proper moisture levels and
developing a systematic inspection and clean-up program to
keep bins, delivery trucks and other equipment free of adhering
or caked feed ingredients are also the most important options.
Minimizing dust accumulation in milling and mixing areas and
treating grains contaminated with aflatoxins by ammonia have
also been successfully inclusive method of preventing the disease
but it is expensive and dangerous to do .
The presence and growth of Aspergillus on pre-harvested
crops is dependent on the environment. Agricultural practices
including proper farm system and pest management can reduce
aflatoxin contamination. Controlling or reducing infection
by regulating the factors that increase the risk of aflatoxin
contamination in the field contributes extensively in managing
aflatoxin. Management practices that reduce the incidence of
aflatoxin contamination in the field include timely planting,
maintaining optimal plant densities, proper plant nutrition,
avoiding drought stress, controlling other plant pathogens, weeds
and insect pests and proper harvesting . Another potential
means for aflatoxin control is the biocontrol of fungal growth in
the field. Numerous organisms have been tested for biological
control of aflatoxin contamination including bacteria, yeasts, and
non-toxigenic (toxigenic) strains of the causal organisms of which
only toxigenic strains have reached the commercial stage . Soil
testing, field crop rotation, antifungal chemical treatments (for
example, proprionic and acetic acids), and adequate insect and
weed prevention. Harvesting strategies include use of functional
harvesting equipment, clean and dry collection/transportation
equipment, and appropriate harvesting conditions (low moisture
and full maturity). Postharvest measures include use of drying as
dictated by moisture content of the harvested grain, appropriate
storage conditions, and use of transport vehicles that are dry and
free of visible fungal growth [46,47].
Sorting out of physically damaged and infected grains from
the intact commodity can result in 40-80% reduction in aflatoxin
levels. The advantage of this method is that it reduces toxin
concentrations to safe levels without the production of toxin
degradation products or any reduction in the nutritional value
of the food. This could be done manually. Market practices such
as grading have also been shown to reduce levels of aflatoxin
. Clearing the remains of previous harvests and destroying
infested crop residues are basic sanitary measures that are also
effective against storage deterioration. Cleaning of stores before
loading in the new harvests was correlated with reduction in
aflatoxin levels. Wild hosts, which constitute a major source of
infestation for storage pests, should also be removed from the
vicinity of stores. These improved postharvest technologies have
been used successfully to reduce the blood aflatoxin .
Aflatoxin regulatory programs are already in place in most
countries to the export side these regulatory programs are
strictly enforced to protect the export market of agricultural
commodities, otherwise the importing countries would reject
the commodities resulting in a loss of valuable foreign exchange
earnings. Domestic regulatory measures on aflatoxin have
received very little attention and are enforced, with no incentives
given for the aflatoxin free produce and no heavy penalty on the
violators of aflatoxin regulations.
To reduce the losses due to aflatoxin contamination risks
must be solved through using sanitary measures during pre
harvest, harvest postharvest handling of food and feeds of
animals. Multi-sectoral approaches programs are required at all
levels to control aflatoxin contamination and improve the quality
of product to security and health assessments of communities.
Aflatoxin control program will include complementary
components such as relevant information standards regulations
policy to distribute safe and high quality food to fulfil consumer’s
Many chemical preservatives have been used for the control
of Aspergillus food contamination such as fungicides, herbicides
and insecticides for healthier plants that resist fungus .
The widespread use of chemical preservative has significant
drawbacks including increased cost, handling hazards, concern
about residues of pesticide on food and threat to human health
and environment. There is no specific antidote for toxicity of
aflatoxins. However; timely administration of l-methionine
(200mg/kg) and sodium thiosulfate (50mg/kg) at eight-hour
intervals is proven to be of therapeutic value. Supplementation
with increased levels of protein, vitamins and antioxidants can
also be rewarding .
Food has always played an extra-ordinarily vital role in the
growth or fall of a nation. Consumption of unsafe contaminated
food leads to food borne diseases which cause considerable
morbidity and mortality. Aflatoxin contamination of foods and
feeds is a serious worldwide problem resulting either from
improper storage of commodities or pre harvest contamination.
So its contamination is a global food security issue, especially in
developing countries as limite freedom of choicing food.
It is limited for a poor and food insecure population. Its
presence in food products and animal feeds is an important
problem concerned with food and feed safety. Significant
economic losses are associated with their impact ton human and
animal health. The contamination in food commodities threat
does follow the rules of dosage to response and association with
health risks in both animals and humans. They also have greater
attention than any other mycotoxins because of their potent
acute toxicological and carcinogenic effect in susceptible animals
and humans, as well as the economic impact drive directly from crops, livestock and their product losses, and indirectly
from the cost of regulatory programs designed to reduce risks
of animals and humans health. Lacks of sanitary measures on
food commodities usually contaminated with aflatoxins mould
growth is an unavoidable and may pass through manufactures
and cooking processes [53,54].
Based on the above conclusion, the following
recommendations are forwarded:
a. Natural contaminants of food chain with aflatoxin
should be reduced by using sanitary measures and a
multiface awareness approach.
b. Primary products such as cereals and animal products
should be screened routinely for aflatoxins.
We would also like to express our gratitude to Mekelle
University and Wollega University, College of Medical and
health science, School of Veterinary Medicine Staff of School
of Veterinary Medicine for inspiration and moral support that
enabled to prepare this Seminar paper.
“Abriham kebede Deresa has contributed to design the title
and reviewing the manuscript to be ready for publication”.
“Abebe Belina and Yobsan Tamiru have participated in the data
collection from different pdf and compile the manuscript. All
authors read and approved the final manuscript”.