Pigeon fever

Pigeon fever is a disease of horses, also known as dryland distemper or equine distemper, caused by the Gram-positive bacteria Corynebacterium pseudotuberculosis biovar equi.[1] Infected horses commonly have swelling in the chest area, making it look similar to a 'pigeon chest'. This disease is common in dry areas. Pigeon Fever is sometimes confused for Strangles, another infection that causes abscesses.

Symptoms

There are three common forms of pigeon fever that affect horses; ulcerative lymphangitis, external abscess, and internal infection. The severity of symptoms varies depending on various factors such as age, immune system, health and nutrition. The bacteria has an incubation period of 3–4 weeks.[2]

Ulcerative lymphangitis

This is the least common form of pigeon fever seen in horses. It is characterized by severe limb swelling and cellulitis in one or both hind limbs and can lead to lameness, fever, lethargy and loss of appetite. Antimicrobial and anti-inflammatory treatments are required to prevent further complications such as limb edema, prolonged or recurrent infection, lameness, weakness and weight loss.[3]

External abscess

External abscesses are the most common form of pigeon fever seen in horses. Abscesses develop on the body, usually in the pectoral region and along the ventral midline of the abdomen. However, abscesses can also develop on other areas of the body such as the prepuce, mammary gland, triceps, limbs and head. The fatality rate for this form infection is very low. The abscess is often drained once it has matured.[3]

Internal infection

Only 8% of infected horses have this form of pigeon fever, however, it has a 30-40% fatality rate. Organs that are commonly affected are the liver, spleen, and lungs. For a successful recovery, long-term antimicrobial therapy is essential.[2]

Treatment

Treatment depends on many factors, such as the age of horse, severity of symptoms and duration of infection. As long a horse is eating and drinking, the infection must run its course, much like a common cold virus. Over time a horse will build up enough antibodies to overtake and fight the disease. Other treatment options can be applying heat packs to abscesses to help draw it to the surface and using drawing salves such as Ichthammol. A blood test or bacterial cultures can be taken to confirm the horse is fighting Pigeon Fever.[3] Anti-inflammatory such as phenylbutazone can be used to ease pain and help control swelling. Treating Pigeon Fever with antibiotics is not normally recommended for external abscesses since it is a strong bacterium that takes extended treatment to kill off and to ensure it does not return stronger. However, if the abscesses are internal then antibiotics may be needed.[4] Consulting a veterinarian for treatment is recommended. Making the horse comfortable, ensuring the horse has good food supply and quality hay will help the horse keep their immune system strong to fight off the infection. Once the abscess breaks or pops, it will drain for a week or two. During this time keeping the area clean, applying hot packs or drawing salves will help remove the pus that has gathered in the abscess.

Transmission

This bacterium is present in soil and is transmitted to horses through open wounds, abrasions or mucous membranes.[3]

Prevention

It is important to reduce the amount of environmental contamination to prevent the spread of insects or fomites. Owners should regularly apply insect repellent and routinely check their horses for open wounds to prevent chance of infection.[3] A regular manure management program is recommended, including removal of soiled feed and bedding, as the bacteria can survive in hay and shavings for up to two months.[3] Since the disease lives in the ground and is spread by flies, pest control is a good defense but not a guarantee. Horses being introduced to new environments should be quarantined and any infected horses should be isolated to prevent spread of the bacteria.[2] There is currently no vaccination for Pigeon Fever.[2]

Epidemiology

The disease can occur in horses of any age, breed or gender.[5] In the US, it occurs throughout the country and at any time of year.[6] The disease was traditionally thought to occur mainly in dry, arid regions,[5] but from at least 2005, its range has been increasing into areas where it was not previously seen, such as the Midwestern US,[7] and Western Canada.[8] Environmental risk factors include over 7 days of a weekly average land surface temperatures above 35 °C, and drier soils; these factors were implicated in an outbreak in Kansas in 2012.[5]

References
  1. Baraúna, RA; Ramos, RT; Veras, AA; Pinheiro, KC; Benevides, LJ; Viana, MV; Guimarães, LC; Edman, JM; Spier, SJ; Azevedo, V; Silva, A (26 January 2017). "Assessing the genotypic differences between strains of Corynebacterium pseudotuberculosis biovar equi through comparative genomics". PLoS ONE. 12 (1): e0170676. doi:10.1371/journal.pone.0170676. PMC 5268413. PMID 28125655.
  2. University of California - Centre for Equine Health (2014). "Pigeon Fever: Varying forms of infection in horses" (PDF). Retrieved December 4, 2016.
  3. American Association of Equine Practitioners (2013). "Pigeon Fever" (PDF). Retrieved December 4, 2016.
  4. Sharon J. Spier
  5. Boysen, C; Davis, EG; Beard, LA; Lubbers, BV; Raghavan, RK (16 October 2015). "Bayesian geostatistical analysis and ecoclimatic determinants of Corynebacterium pseudotuberculosis infection among horses". PLoS ONE. 10 (10): e0140666. doi:10.1371/journal.pone.0140666. PMC 4608828. PMID 26473728.
  6. Kilcoyne, I; Spier, SJ; Carter, CN; Smith, JL; Swinford, AK; Cohen, ND (1 August 2014). "Frequency of Corynebacterium pseudotuberculosis infection in horses across the United States during a 10-year period". Journal of the American Veterinary Medical Association. 245 (3): 309–14. doi:10.2460/javma.245.3.309. PMID 25029310.
  7. Barba, M; Stewart, AJ; Passler, T; Wooldridge, AA; van Santen, E; Chamorro, MF; Cattley, RC; Hathcock, T; Hogsette, JA; Hu, XP (2015). "Experimental transmission of Corynebacterium pseudotuberculosis biovar equi in horses by house flies". Journal of Veterinary Internal Medicine. 29 (2): 636–43. doi:10.1111/jvim.12545. PMC 4895518. PMID 25818218.
  8. Corbeil, LE; Morrissey, JF; Léguillette, R (October 2016). "Is Corynebacterium pseudotuberculosis infection (pigeon fever) in horses an emerging disease in western Canada?". The Canadian Veterinary Journal. 57 (10): 1062–1066. PMC 5026146. PMID 27708444.
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