In 2017, the world population of ducks was estimated at 1.15 billion. One billion was in Asia, which accounts for the countries with the largest population of ducks: China, which concentrates 60% of the world’s production, Vietnam, Bangladesh, and Indonesia.

Ducks are known to be relatively disease-resistant and are considered potential carriers of infectious diseases of other birds. Some critical diseases in broiler production, such as coccidiosis or infectious bronchitis, are not usually as economically relevant in duck production. This article presents the main pathologies in duck production according to their prevalence in China and their etiology: toxicosis or infectious (bacterial, viral, or fungal) origin.

Mycotoxins

Ducks are especially sensitive to toxins, and cases of high mortality related to toxicosis are common. Common causes include botulinum toxin, lead, overmedication with certain antibiotics, and mycotoxins.

Mycotoxins are one of the main challenges in duck production. The toxicity of mycotoxins in ducks has not been as studied as in broilers, despite their high sensitivity to these molecules. Aflatoxin is one of the most common mycotoxins in food worldwide. Ducks are about 200 times more sensitive than broilers and layers, because they metabolize this molecule differently (more bioactivation of the molecule and less detoxification and elimination than in broilers).

In addition, the presence of several mycotoxins in the food, a very frequent fact, is especially dangerous for this species. Internal organs, such as the liver or the immune system, are the most affected by the presence of mycotoxins in duck food. Therefore, it is important to perform a quality control of the feed and raw materials, as well as add a mycotoxin binder in the feed.

Viral diseases

• Duck viral enteritis

Duck viral enteritis, also called duck plague, is caused by a herpesvirus, and can affect animals of all ages, although it usually affects ducks over 5 weeks of age, where the presentation is more severe and has a greater economic impact.

It is transmitted orally between infected animals or through water. The presentation of the disease and mortality vary according to the age and immune status of the animal, as well as the virulence of the virus.

The first signs are usually high and persistent mortality, nasal discharge, polydipsia and watery or bloody diarrhea.  Dehydration, weight loss and lower mortality are usually observed in young animals.  In layers, a considerable decrease in egg production is observed. If partial immunity exists, deaths are occasional, and the presentation tends to be chronic.

Affected animals show hemorrhagic lesions and necrosis in internal organs (such as the heart, liver, and lymphoid organs) and throughout the animal’s gastrointestinal tract. Hemorrhagic lesions in the digestive system can evolve and coalesce, covering the mucosa with a diphtheroid membrane. Birds that survive the disease can continue to be carriers and act as reservoirs of the virus.

There is no treatment for this disease, so prevention is essential, based on biosecurity and vaccination of breeding and fattening batches.

• Viral hepatitis of the duck

Duck viral hepatitis is a highly contagious viral disease of mandatory notification and of great economic importance, caused by three genotypes of the hepatitis A duck virus (HCAP), a picornavirus.

Susceptible animals are less than 6 weeks-old, mainly young ducks up to 30 days of age. The younger the animal, the more susceptible it is to the disease. Adult birds do not show clinical signs. The virus spreads rapidly horizontally and within few days, morbidity can reach 100% and mortality up to 95%.

It is a disease with an over-acute presentation, which includes lethargy, ataxia, or spasmodic contractions, followed by opisthotonos and death. Lesions observed are hepatomegaly, hemorrhages and/or liver necrosis. Renal splenomegaly and swelling may also appear.

Prevention of this disease is based on vaccination of breeding animals to induce passive immunity to the offspring.

• Avian influenza

In many cases, ducks can be infected at the respiratory or digestive level with the avian influenza virus and show no symptoms, although there are certain strains that can cause illness and even death of this type of animal. Generally, the duck is considered a reservoir of this type of virus.

• Emerging disease: Duck egg-drop syndrome

Several countries in Asia have shown this disorder since 2010. It is characterized by a severe decrease in the egg production rate of laying and breeding ducks, along with anorexia, diarrhea, and severe neurological disorder (ataxia and paralysis), with high morbidity and a variable mortality of 5-30%.  The resulting economic losses are very high and the main lesions, of hyperemic or hemorrhagic nature, are at the oviduct and ovary.

In these cases, a virus, called BYD virus, has been isolated, which designates the region of Baiyangdian (China) where the virus was first isolated. This virus complies with Koch’s postulates, and is related to the Tembusu virus, a mosquito-borne disease of the flavivirus group, which can also infect other species of birds, and even humans (farm workers tested positive for the infection, although the disease has not yet been reported).

Bacterial diseases

• Riemerella anatipestifer Infection – Infectious Serositis

Riemerella anatipestifer causes an infection with high morbidity and mortality in susceptible flocks. It has a presentation similar to Pasteurella spp. It can affect ducks of all ages, although it is more frequent in young animals and in intensive farms with animals of different ages.

The transmission of the disease is not clearly defined, although it is believed that animals can become infected by airborne route and through feet wounds, so the lack of hygiene provides the ideal environment for the spread of the disease. The disease can be endemic once it appears on the farm.

Animals suffer from diarrhea, ocular and nasal discharge, respiratory signs such as coughing and sneezing, and nervous signs including incoordination, tremors, paralysis, or seizures. Mortality is variable (5-50%), although it can reach 75%.

The most frequently observed lesions include the presence of inflammation with fibrinous exudate in the pericardium, liver, and air sacs, although it can also affect the lung, joints, and the nervous or reproductive system.  It is very common to observe mixed infections with E. coli, with septicemic lesions.

The prevention of the disease includes the maintenance of a high level of biosecurity, cleaning, and disinfection on the farm, along with the immunization of animals. Vaccination has its limitations in this disease because there are multiple serotypes without cross-immunity. Commercially available vaccines typically include the three most common serotypes.

• Avian cholera

Avian cholera, caused by the bacterium Pasteurella multocida, is a disease of great relevance in duck production in Asia. Ducks are more susceptible than chickens. The presentation of the disease varies depending on its presentation and it is usually associated with poor hygiene and the presence of stagnant water in the pens.

The acute presentation may include an outbreak of mortality without previous signs, while in more advanced cases depression, anorexia, respiratory distress, mucous discharge from the mouth and diarrhea may be observed. In chronic cases, the infection can cause conjunctivitis, and can be located in joints and wattles containing fibrinous exudate.

Fungal diseases

• Aspergillosis

This disease occurs by inhaling spores produced by the fungus Aspergillus, mostly Aspergillus fumigatus, which is transmitted through contaminated wet feed. The growth of this fungus causes nodules or plaques in the lungs.

Conclusions

Ducks are relatively resistant to diseases, although there are certain challenges that this industry can face. The main challenges in duck production are of infectious or toxic origin.

It is essential to control the microbiological and toxicological quality of the feed using feed preservatives, to prevent the growth of pathogenic fungi and bacteria, as well as using mycotoxin binders to control the impact of these type of toxins on the productivity and immune status of the batch.

The use of a Silicoglycidol-based mycotoxin binder allowed to achieve better weight (+66 g/bird) and better conversion rate (-1.06%) in Pekin ducks fed an aflatoxin-contaminated diet aflatoxin (75 ppb).

In relation to infectious problems, it is essential to carry out a correct biosecurity plan of the farm to prevent the contact of wild animals with the domestic animals, the feed and the drinking water, as well as to carry out a correct cleaning and disinfection of the facilities and avoid mixing animals of different ages on the farm. In situations where the challenge is high, it is recommended to establish a vaccination plan in breeding and/or fattening animals.

The use of immunostimulant products allows animals to maintain a good immune status and achieve a better immune response after vaccination and, therefore, greater protection against the disease.

Sources:

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