Real hazards of mycotoxins to avian and public health

mycotoxins avian public health


AUTHOR

Fernando Moreira

Mycotoxins consitute a  hazard to both avian and public health, especially when mycotoxin residues remain in poultry tissues and eggs. This is a serious issue that need to be adressed by all stakeholders, especially health authorities. This article discusses the effect of different mycotoxins in poultry, the entry of mycotoxins in the food chain through poultry products, and the occurrence of mycotoxicosis in humans. Strategies for the control of the problem at the animal feeding level are also proposed. 

Introduction

The Food and Agriculture Organization of the United Nations (FAO) estimates that approximately 25% of the world’s food crops are contaminated with mycotoxins.

The term “mycotoxin” was created in 1962 after an outbreak with high mortality of turkeys in England. The cause was identified as the use of peanut meal from Brazil and Africa.

Mycotoxins are secondary metabolites produced by heterogeneous fungi. When present in feeds and foods, mycotoxins can affect the organism, leading to yield losses and pathological changes called mycotoxicosis.

 

Avian Health

In poultry production , these toxins can have a negative impact on productivity. Therefore, it is very important to understand how the different types of mycotoxins affect poultry health so that they can be counteracted, and economic losses are prevented.

mycotoxinsDifferent poultry species have also different susceptibilities to mycotoxins.

Ducks, geese and turkeys are more susceptible to mycotoxins than broilers.

Another curious fact is that it is commonly thought that the presence of mycotoxins in early life stages is always more worrying. Recent studies show that, e.g., the presence of deoxynivalenol (DON) can be particularly harmful in the period between 18 and 25 days, which corresponds to the later intestinal growth phase; this affects development closest to the final growth phase.

 

Public health

In human, several epidemiological studies have showed that the effects of some mycotoxins on foods, especially aflatoxins, can be extremely harmful, sometimes causing liver tumors.

The real hazards associated with mycotoxin contamination on the food chain – especially in milk, meat and eggs – should be monitored . This is the responsibility of all stakeholders involved in the production chain, particularly health authorities.

 

 

Mycotoxin classes

There are 6 main mycotoxin classes:

  • Aflatoxins (Aspergillus spp.)

  • Ochratoxins (Aspergillus spp.)
  • Trichothecenes (Fusarium spp.)

  • Fumonisins (Fusarium spp.)
  • Zearalenone (Fusarium spp.)
  • Ergot alkaloids (Claviceps spp.)

In poultry production, the main interactions and factors influencing the production of mycotoxins are:

  • Farm management, including hygiene, humidity and temperature
  • Exposure time
  • Age, gender and species
  • Nutrition and health status of the birds
  • Nature and concentration level of mycotoxins
  • Presence of other toxins

Although there are different effects caused by mycotoxins , it is common that all of them cause immunosuppression and affect general immunity of the birds. Several recent studies confirm that broilers are sensitive to the presence of Fusarium mycotoxins. Moderate levels of these mycotoxins negatively affect the appetite and growth of the birds.

 

Aflatoxins

Aflatoxin is one of the main and most frequently observed mycotoxins in animal production. 

Clinical signs in poultry:

  • Can present as acute or chronic aflatoxicosis.
  • reduced feed intake
  • weight loss
  • reduced egg production
  • paleness of the mucosa
  • paleness of legs and beak
  • increased bruising
  • immunodepression
  • increased mortality

Lesions:

  • Liver lesions are more frequent and are characterized by enlargement, friability, paleness and a marked hepatic fatty infiltration.
  • Swollen spleen and kidneys.
  • Reduced size of bursa of Fabricius and thymus.
  • Petechial hemorrhages in muscles (reduced coagulation factors and increased capillary fragility).
  • Tumors (Carcinogenic and teratogenic).

Figure 1. Broiler liver presenting lesions consistent with aflatoxicosis.

Ochratoxin A (OTA)

Clinical signs of ochratoxicosis in poultry:

  • reduced weight gain
  • depression
  • dehydration
  • reduced egg production and hatching rate
  • survivor birds show atrophy, poor feathering, anemia and immunodepression

Lesions observed at necropsy:

Enlarged kidneys, white or yellowish in color (white effusions of urate crystals).

Urate deposition on pericardial, perihepatic, peritoneal and articular surfaces.

Survivor birds show:

  • enlarged, fibrotic and pale kidneys (renal compensation)
  • fatty liver
  • reduced size of bursa of Fabricius and thymus, immunodepression

Figure 2. Broiler kidneys presenting lesions consistent with the intoxication woth OTA.

Trichothecenes

The clinical signsin birds fed excessive levels of trichothecenes (primarily T-2 toxin) are:

  • reduced appetite
  • reduced weight gain
  • bloody diarrhea
  • anemia
  • poor feathering

Oral lesions, reduced egg production, poor eggshell quality and reduced hatching rates were observed in adult birds.

The lesions are highly characteristic:

  • ulcers in the corner of the mouth, hard palate, choana and dorsal surface of the tongue (3 to 4 days after infection)
  • reduced size of bursa of Fabricius and thymus
  • anemia
  • pale bone marrow
mycotoxins

Figure 3. Lesions consistent with T-2 toxin.

Fumonisins

As corn is an important raw material added to poultry diets, particular attention is given to fumonisins.

Most commonly observed clinical signs include:

  • reduced feed intake
  • reduced weight gain
  • diarrhea

Lesions (unspecific):

  • catarrhal enteritis
  • hepatomegaly
  • possible increase in the size of kidneys, pancreas, proventriculus and gizzard
  • reduced size of bursa of Fabricius and thymus
  • anemia
  • pale bone marrow

 

Zearalenone

The presence of zearalenone can affect the reproductive tract. Therefore, they are more relevant to adult birds, where the sexual secondary characteristics are more evident, causing thickening of the cloacal mucosa.

 

 

Differential diagnosis of mycotoxicosis in poultry

  • Aflatoxicosis: Infectious bursal disease, fatty liver syndrome, malabsorption syndrome, and amyloidosis.
  • Ochratoxin: Aflatoxicosis, visceral gout, infectious bronchitis, sodium poisoning, water deprivation, vitamin A deficiency, and malabsorption syndrome.
  • Fusarium toxins: Avian pox (wet form), vitamin A deficiency, trichomoniasis, ochratoxicosis, aflatoxicosis, leg weakness, and infectious bursal disease.

 

 

What is the effect of avian mycotoxicosis in public health?

Added to the toxic effects on livestock animals, the passage of mycotoxins to the food chain (e.g. in poultry meat, viscera, and eggs) constitutes a real danger and needs more attention. The levels of mycotoxin residues in food for human consumption are regulated by government organisms. For example, legislation in the European Union can be consulted in:

  • Food legislation: EU (2006b, 2007, 2010a, 2010b)
  • Animal feed legislation: EU (2003)
  • Dietary guidelines: EU(2006a,b)

Several research studies examined (through different methods) eggs, meat, and offal from laying hens and broilers fed diets containing high levels of mycotoxins. Those studies also analyzed the potential hazards of mycotoxins to public health.

Now it is known that the consumption of viscera, especially liver, constitutes a greater risk than meat consumption. This is because most mycotoxins are metabolized in the liver, where they consequently concentrate.

Food chain contamination with mycotoxins poses a risk to public health. Affected individuals may present acute aflatoxicosis and hepatocellular carcinoma, mainly in Asian and African risk countries.

Human beings may be exposed to a complex and variable combination of mycotoxins. After their ingestion, the intestinal mucosa is the first biological barrier at risk of being expposed to high mycotoxin concentrations. The high risk posed by long-term exposure to contaminated foods forces modern science to develop and implement effective methods to counteract mycotoxins.

 

Effects of zearalenone in humans

Studies indicate that the exposure to this Zearalenone can cause changes in body’s hormonal balance. This may result in reproductive disorders, such as prostate cancer, ovarian cancer, cervical cancer and breast cancer. However, a research trial conducted in China in 2018 examined foods highly contaminated with zearalenone. The results showed that high levels of this mycotoxin in broiler tissues did not present any risk to public health.

 

Effects of trichotecenes

T-2 toxin has also been extensively studied and found in food products. Its has a neurotoxin effect, with severe implications for human health.

The maximum level permitted by the European Food Safety Authority (EFSA) for T-2 toxin in broiler feeds is 0.25 mg/kg.

In the most recent studies, predicted daily intakes in different countries were lower than the average daily intake determined by EFSA, suggesting that EFSA reference levels present a minimal risk.

An interesting and obvious fact reported in these studies is that higher  concentrations of mycotoxins in animal feed result in higher the levels of residues in animal tissues. This represents a higher risk to public health.

After the contaminated feed is eliminated, the residual levels in animals are rapidly reduced to acceptable levels. Many of the maximum levels permitted for different mycotoxins are not yet clear and their real hazards for public health should be investigated, particularly in the case of multiple mycotoxins.

New methods of analysis are currently under investigation. The problem associated with these methods is the number of existing mycotoxins, which makes them economically unsustainable in a demanding analytical program. Also, many of these methods are very time consuming, and many are specific to a particular mycotoxin.

 

Effects of aflatoxins and ochratoxins in humans

Special attention is given to aflatoxin M1, designated by the International Agency for Research in Cancer (IARC) as a possible predisposing factor for human cancer. Ochratoxin A (OTA) has been associated with renal tumors and progressive nephropathy, inflammation, and oxidation.

 

Strategies for mycotoxin control 

Mycotoxin avian public health

 

As mentioned above, the European Union has imposed limits on some of the most common mycotoxins. Many studies confirm that birds fed diets containing mycotoxin levels within the legal limits do not pose any risk to public health, as the toxins are rapidly metabolized by the birds.

  • As a prevention strategy in the field and during cereal storage, we should monitor the humidity content (should be approximately 12%), the relative humidity (should be less than 60%), and the storage temperature (should be lower than 20 ºC).
  • In the feed mill, all the received cereals should be analyzed for mycotoxins using a consistent sampling method.
  • The control of insects and rodents is fundamental.
  • Prevent that the grains are exposed to extreme conditions, such as frost, high  temperatures, and pH changes.
  • Use a good mycotoxin adsorbent in all production stages.

 

 

Reminders

It is very difficult to predict the risk of mycotoxicosis, as most of the time the effects are subclinical.

→ The only way to control mycotoxins in feed and food production is through prevention, never forgetting that the economic impact is higher than the prevention cost.

Food chain contamination poses a risk to animal and public health. The recognition of this fact is the first step towards the international consensus on this subject.

→ The exporting countries and their authorities should be aware of this problem and take measures to ensure that contaminated foods, feeds or grains are not introduced into the importing countries.

→ In recent years, we have witnessed an important climate change. It is expected that the mycotoxin contamination in raw materials increases within the next years.

→ Overall, all parties concerned should take appropriate actions to prevent and reduce this problem.

 

References available on request.

 

 

 

 

This article was originally published in agriNews Spain, under the title Peligros de las micotoxinas para la salud de aves y salud pública

 




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