Porcine atrophic rhinitis is an infectious disease that affects the respiratory system of pigs and has a major impact on production.

The nasal turbinates are a structure formed by spongy bone whose function is to heat, humidify and filter the air that the animals breathe. These are in the nasal cavity and are distributed two in the dorsal portion and two in the ventral portion. When these turbinates are affected, the respiratory function begins to be affected, as in the case of atrophic rhinitis in pigs.

What is porcine atrophic rhinitis?

Porcine atrophic rhinitis is an infectious disease of the upper respiratory tract caused by the bacterium Bordetella bronchiseptica in its mild to moderate clinical form. This mild form is characterized by affected pigs with serous or mucopurulent nasal discharge, a shortened or deformed muzzle, and reduced production.

However, when there is only one infection with Bordetella bronchiseptica the atrophy of the nasal turbinates is regressive (or non-progressive). On the other hand, when there is coinfection with toxigenic strains of Pasteurella multocida, this bacterium worsens the clinical picture severely. In atrophic rhinitis caused by both bacteria at the same time, pigs suffer progressive and complete atrophy of the nasal turbinates. This ends up severely affecting the respiratory function and, consequently, other physiological functions of the pigs.

This bacterial disease is distributed worldwide and affects intensive swine production. Studies in Mexico report a prevalence of 54% of lesions compatible with atrophic rhinitis in swine farms in the Yucatan region. In the United States, 69% of lesions compatible with RAP were reported and in England, 75% of pigs sampled were positive for RAP. (Torres-León, M., et. al, 2000).

How is RAP transmitted?

There are two main routes of transmission for atrophic rhinitis in swine. Vertical transmission occurs when breeding sows that are carriers transmit the bacteria to piglets during lactation. There is no transmission of these bacteria through semen or embryo transplantation.

Another route of transmission is by horizontal transmission when infected piglets shed the bacteria in their feces 2-3 weeks post-weaning. In addition, there is also transmission by aerosols, being affected mainly piglets between 5 to 8 weeks of life.

On the other hand, the concentration of ammonia in the environment must be considered. This compound is generated as a gas from the decomposition of urine and feces in the pig house. Ammonia gas in the air is breathed in by the pigs and has an irritating effect on the respiratory mucosa. This hinders the proper functioning of the cilia in the elimination of bacteria present in the respiratory tract.

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This harmful effect of ammonia predisposes animals to bacterial infections such as Pasteurella spp. or Bordetella spp. and contributes to their transmission.

Finally, the immune status of the group of animals determines the appearance of clinical signs. Sometimes it may be in these piglets or breeding sows, and other times in more adult pigs.

What are the signs of atrophic rhinitis in pigs?

Acute signs of progressive atrophic rhinitis in pigs occur between 3-8 weeks of age. Some of the signs observed are sneezing, coughing, inflammation of the tear duct. If the condition is severe, these tear ducts may become occluded. In addition, affected pigs may have a shortened upper jaw or atrophied turbinates without obvious external signs.

Clinically, it is difficult to observe the degree of distortion of the nasal turbinates. However, if the characteristics of each breed are considered, the ratio of the upper and lower incisors can be judged.

On the other hand, porcine atrophic rhinitis has an impact on production. On the one hand, a slower growth rate is observed in piglets. In more developed animals, the feeding conversation rate starts to be low and even weight loss is observed.Table 2. Grades of lesions of atrophic rhinitis in pigs and their anatomical characteristics.

Impact of RAP on production

The impact on the production of atrophic rhinitis in swine is related to the presence of toxigenic variants of Pasteurella multocida. In addition, herd immunity plays a key role in this pathogenic effect. The vaccination status, as well as the farrowing distribution of the sows, influence this immunity. On the other hand, it should be noted that younger sows produce less immunity through colostrum than sows with several farrowings.

On the other hand, different virulence factors have been identified in the bacterium Bordetella bronchiseptica. These factors are regulated by a translation system encoded in the bvg locus. Among the virulence factors highlighted in this bacterium are adhesins, filamentous hemagglutinins, pertactin and fimbriae. The toxins adenylate cyclase hemolysin and dermonecrotic toxin (DNT) have also been found. The latter has been pointed out as the protagonist in the atrophy of the nasal turbinates and their replacement by connective tissue (Brockmeier, 2002).

How is this disease diagnosed?

The diagnosis of atrophic rhinitis in swine is mainly made by necropsy. However, other complementary laboratory tests allow a more accurate diagnosis.

• Necropsy: For this, a transversal cut of the pig’s snout is made at the level of the first-second upper premolar. In this cut, the degree of atrophy of each nasal turbinate is evaluated: two upper and two lower.
• Bacteriological culture: sampling is performed by nasal swabbing or through pulmonary lavage which is cultured on MacConkey agar. However, this method does not detect toxigenic strains.
• Serology: agglutinating antibodies are detected in serum, but its disadvantage is that it does not differentiate infected from vaccinated pigs.
• Polymerase Chain Reaction (PCR): The PCR test allows the identification of toxigenic strains of Pasteurella multocida type D. It is a highly sensitive method that allows finding the root cause of the problem.

Other diseases of a similar course that should be differentiated from atrophic rhinitis in swine are swine influenza, Aujeszky’s disease, Mycoplasma hyorhinis, PRRS.

Control of atrophic rhinitis in swine

Control of the bacteria causing atrophic rhinitis in swine is difficult because they are microorganisms presented in the environment. Pig farms rarely manage to keep their animals free of mild sneezing. As a result, injured turbinates and nasal bones are sometimes observed, even if there are no clinical signs. Some of the control measures are:

1. Vaccination: there are vaccines available in the market with inactivated strains of both Bordetella bronchiseptica and toxigenic Pasteurella multocida type D. These vaccines prevent the appearance of atrophic rhinitis in swine.
2. Herd immunity: The vaccines provide herd immunity when sows are vaccinated 4 to 2 weeks before farrowing. On the other hand, piglets can be vaccinated between 1 to 4 weeks of age. Typically, sows are vaccinated 4 and 2 weeks before farrowing, and piglets are vaccinated at 1 and 4 weeks of age. In addition, colostrum contains antibodies that protect pigs in the first few days of life.
3. All in all out. This principle is a basic component of farm biosecurity as it allows maintaining minimal or no pathogen loads on the farm. For this purpose, it avoids the exit or entry of animals or materials from other farms with unknown sanitary status.
4. Improved management: some management strategies are a complement to combat atrophic rhinitis in swine. Some of these are improving the ventilation of pig houses, providing less dusty feeding that irritates the nasal cavity of pigs, improving cleaning and hygiene conditions.
5. Chemoprophylaxis: this control measure is focused on the administration of antibiotics to all sows before farrowing. Sometimes, they are also administered to newborn piglets or weaned pigs. Antibiotics such as ceftiofur, sulfonamides, tylosin, and tetracyclines are generally used.

Conclusions

Atrophic rhinitis of swine is a disease of infectious origin caused by bacteria. Its severity depends on the bacteria involved. This infection causes severe lesions in the respiratory tract of pigs.

Transmission of the disease occurs vertically between sows and piglets during lactation. There is also horizontal transmission between animals on the farm.

Lesions can range from absence of lesions to total loss of the nasal turbinates and involvement of the nasal septum. Atrophic rhinitis in pigs has a major impact on pig production.

The diagnostic tests developed focus on finding the presence of the bacteria and strains causing the outbreaks. Then, control and prevention measures should be implemented in the affected farms.

REFERENCES

Brockmeier, S. L., Register, K. B., Magyar, T., Lax, A. J., Pullinger, G. D., & Kunkle, R. A. (2002). Role of the dermonecrotic toxin of Bordetella bronchiseptica in the pathogenesis of respiratory disease in swine. Infection and immunity, 70(2), 481-490.