Recently, the Swine Health Information Center (SHIC) reported an increased incidence of Hemorrhagic Tracheitis Syndrome (HTS) issues in finishing pigs in North America. The following is a summary of current understanding about the condition, what producers should look for, and the work to find a solution.

History
Scattered reports of tracheitis or HTS cases have historically been described in Canada. A few systems in the eastern United States have seen a small number of cases that began about a decade ago, but recently this syndrome has grown more widespread to affect more systems, areas, and producers. Multiple veterinary clinics, diagnostic labs, and producers are working together to investigate this issue. The goal is to help define what a case looks like, search for any underlying cause, and hopefully find solutions for HTS.

Indicators of HTS
Often the first signs in barns affected with HTS is a drop in water consumption a few days prior to onset of cough. This cough is described as extra loud, sometimes likened to a goose honk, or a high-pitched squeak or barking hack. The cough spreads quickly through the barn in 1-2 days. Up to 30% of the barn may be affected. This cough is significant and severe, unlike the typical coughs we hear frequently in finishing pigs due to respiratory diseases like flu or Mycoplasma hyopneumoniae (MHP). Most cases are in grow/finish age pigs greater than 10 weeks of age, with older pigs affected more severely. This cough tends to last for 5-10 days. Early cases have reported up to an 8-10% increase in mortality. Mortality can be minimized to 2-4% above normal levels if the cough is minimized or controlled at the barn level. Affected pigs and pens do not seem to follow any specific pattern in the barn. Relapses of HTS in previously affected pigs in a barn have not been reported. Affected barns have not reported having issues from the packing plant. This syndrome does not seem to follow any certain path to affect barns. No regional, geographical, or flow of pigs has been correlated with the syndrome. There does not 0seem to be any genetic line or predisposition for HTS. It does not seem to be affected by health status of the barn (i.e. PRRS, MHP, Flu). The number of cases seems to be highest in the fall and then gradually decrease throughout the summer.

At the individual pig level, a producer in an affected barn will typically hear a low number of around 5-10 pigs out of 1000 coughing when entering the barn. Identifying those individual pigs may require entering the pen. Stirring R pigs up will help stimulate this cough and allow the producer to assess how widespread it is in the barn. Severely affected pigs often do not survive. Less severely affected pigs tend to survive following segregation from the general population and treatment. Light or smaller pigs in the barn do not seem to be affected as often as those who happen to be larger. When affected pigs are posted, the inside lining of the trachea is usually found to be moderately to severely swollen, creating an hourglass-like shape in the trachea instead of the round form found in a healthy animal. Often the area of the trachea most affected is where it enters the chest. Upon examination in the lab, the swollen tissue generally appears to be an acute or recent event that triggers the swelling. This swelling on the inside of the trachea is what causes the noise and difficulty breathing. Some cases have reported swollen lymph nodes on one side of the trachea. Most affected pigs have little to no pneumonia or disease in the lung tissue.

Testing performed
Multiple labs have been searching for infectious causes of HTS, but no primary underlying condition has been identified. The labs are reporting that in around half of those tissue cases submitted, no respiratory pathogen had been found. In the other half of cases, typical respiratory pathogens like Flu, PRRS, MHP and other bugs have been present. Given the short duration of this syndrome, it has been difficult to identify a primary cause among the many bugs that make pigs cough. Next-generation sequencing has been performed in a few cases so far and has not returned any findings. ISU VDL has compiled a standardized set of samples for submission to identify common links in those affected barns. Mechanical, traumatic, and other causes for swelling in the trachea are still on the list to rule out.

Treatments
No singular type of treatment has been identified as especially useful for HTS. It seems that controlling or minimizing the cough and other secondary herd health issues is important. The use of anti-inflammatory and/or antibiotics also seems to help. Treating individual pigs appears to be the most effective method. Segregating or moving affected pigs to a hospital pen or into the alleyway for relief may help as much as injections. One clinic reported a decrease in HTS cases after focusing on vaccine placement. Other clinics underline the randomness in those barns affected. Producers should work with their herd veterinarian to determine the most effective treatment options for their pigs if HTS is suspected or diagnosed.