Erysipelas is a bacterial infection caused by Erysipelothrix rhusiopathiae. Common clinical signs in poultry are sudden death, lethargy, decreased egg production, cutaneous lesions, and swollen hocks. Diagnosis is by PCR assay or aerobic culture. Treatment is generally with short-acting penicillin. Erysipelas is zoonotic.
Erysipelas is a bacterial disease caused by infection with Erysipelothrix rhusiopathiae. E rhusiopathiae has a wide host range, and infection can occur in avian, mammalian, aquatic, amphibian, reptilian, and insect hosts.
A wide variety of avian species can be infected, and the disease has been reported in poultry as well as in captive and wild bird species. From an economic standpoint, turkeys are the most important poultry species affected; however, serious outbreaks have occurred in chickens, ducks, and geese. Studies suggest a correlation between an increased incidence of erysipelas in layers and the transition from conventional cages to cage-free systems (1).
Among affected mammals, swine are the most economically important species, and diamond skin disease is a common presentation in pigs. E rhusiopathiae infection is also a cause of polyarthritis in lambs.
Erysipelas in poultry is present worldwide, and although it is considered a sporadic disease, endemic areas exist.
Etiology of Erysipelas in Poultry
E rhusiopathiae, the causative organism of erysipelas in poultry, is a gram-positive, facultative anaerobic bacterium. There are multiple Erysipelothrix spp; however, E rhusiopathiae is the only pathogenic species affecting avian hosts.
E rhusiopathiae stains gram-positive; however, older cultures tend to decolorize. The organism is small, non–acid fast, and nonmotile; it does not form spores or produce toxins. It does not have a flagellum, but it does have a capsule. Various factors, including the production of neuraminidase enzyme, affect the bacterium's virulence in attaching to and invading host cells.
Colony morphology of E rhusiopathiae is variable. E rhusiopathiae has three colony types (rough, smooth, and intermediate) and grows readily on culture media containing blood or sera of various animals. Growth is enhanced by decreasing oxygen levels or increasing carbon dioxide levels to 5%–10%. Optimal incubation temperature is 35°C–37°C, and optimal pH range is 7.4–7.8.
Bacterial cells freshly isolated from tissues during acute infection or from smooth colonies are straight or slightly curved small rods that may occur in short chains. Cells from older cultures or from rough colonies tend to become filamentous and may be confused with mycelia. The filamentous form occurs more frequently after repeated passages on artificial media.
There are at least 28 serotypes within the Erysipelothrix genus, based on antigenic classification of heat-stable cell-wall antigens using a double agar-gel precipitation test. E rhusiopathiae serotypes 1, 2, and 5 have been most frequently isolated from poultry.
Epidemiology of Erysipelas in Poultry
Erysipelas occurs sporadically in poultry of all ages. E rhusiopathiae can survive for prolonged periods in the environment, especially when protected in decomposing carcasses and other organic material. Turkeys are susceptible regardless of sex or age, although under field conditions, the disease is more common in birds after the onset of sexual maturity. Erysipelas may contribute to carcass downgrading and processing losses in turkey-processing plants.
Infection results from entrance of the organism through breaks in skin (such as trauma from fighting), through mucous membranes (eg, during artificial insemination), by cannibalism of infected carcasses, and possibly by mechanical transmission via biting insects. The poultry red mite can harbor the organism and may serve as a mechanical vector.
The bacterium is shed in feces from infected animals and contaminates soil, in which it can survive for long periods, depending on temperature and pH. Poultry, as well as other animals, may be carriers and shed the organism without showing clinical signs. Carriers can shed the organism in feces and oral and nasal secretions. Rodents or other infected host species can serve as sources of infection for poultry.
In nonvaccinated flocks, morbidity and mortality rates can reach 40%–50%, but mortality rate is usually < 15%. In vaccinated flocks, some birds may be lethargic for a short period; however, they typically recover. Mortality rates in vaccinated and nonvaccinated poultry are influenced by the virulence of the organism, as well as by host and environmental factors.
The reemergence of poultry erysipelas in some regions, particularly in the layer population, may be multifactorial, with conversion to cage-free, free-range, and organic production systems, as well as climate change and decreased host resistance, each playing a role. Rainy, cold weather coinciding with the onset of sexual maturity increases the risk of clinical disease.
No correlation has been shown to exist between serotype, chemical structure, or biochemical pattern and pathological presentation of erysipelas.
Clinical Findings of Erysipelas in Poultry
Erysipelas in poultry is primarily an acute infection that often results in sudden death. Clinical infection with erysipelas is often associated with septicemia. Erysipelas should be suspected in flocks that have been artificially inseminated 4–5 days before an episode of death without previous clinical signs.
Clinical signs in poultry include generalized weakness, depression, diarrhea, and sudden death. In an affected flock, birds may be listless, and death may occur within 24 hours of the onset of clinical signs. Just before death, some birds may be very droopy, with an unsteady gait.
Most sick birds die before treatment. Turkeys with vegetative endocarditis usually do not have clinical signs and may die suddenly. In laying hens, water consumption and egg production may drop markedly.
Chronic clinical signs of disease in a flock are not usual but do occur and can manifest as swollen joints and gait disturbances due to arthritis.
Lesions
Birds may have cutaneous lesions and swollen hocks.
At necropsy, generalized or localized cyanosis, urticaria, or crusting of skin, especially on the head, snood, and wattles, is common. The liver and spleen are usually enlarged and friable and may be mottled (see erysipelas image, liver and spleen).
Courtesy of Dr. Simone T. Stoute.
Other gross lesions, including conjunctival edema, sanguinous or mucinous intestinal contents, and petechial hemorrhages on the heart, abdominal fat, skeletal muscles, and viscera, may be noted (see erysipelas image, petechial hemorrhages). Generalized congestion, vascular damage, fibrin thrombi, vegetative endocarditis, synovitis, and hepatosplenic necrosis are common microscopic findings.
Courtesy of Dr. Simone T. Stoute.
Diagnosis of Erysipelas in Poultry
Necropsy and impression smears
Identification of E rhusiopathiae
A presumptive diagnosis of erysipelas can be based on necropsy and impression smears of the liver, spleen, cardiac blood, or bone marrow that demonstrate gram-positive, slender, pleomorphic rods.
Isolation or identification of E rhusiopathiae is required for definitive diagnosis. Identification can be made by fluorescent antibody staining, immunohistochemical testing, or PCR assay. Liver and spleen are usually adequate samples for aerobic culture; however, bone marrow is the tissue of choice in partially decomposed specimens (see bacterial colonies image).
Bacteria can be isolated from basic or enriched media. Samples, such as environmental swabs, from potentially contaminated specimens can be cultured on selective media with inhibitory chemicals. Isolation on nonselective media requires vigilant screening of cultures because the organism produces pinpoint colonies that can be easily overlooked or masked by faster-growing bacteria.
Courtesy of Dr. Simone T. Stoute.
Serological surveillance and serotyping and genotyping techniques have been described; however, their use is mainly restricted to research, and these techniques are not routinely available in most diagnostic laboratories.
Differential diagnoses for acute erysipelas in poultry include colibacillosis (infection with Escherichia coli), fowl cholera (infection with Pasteurella multocida), virulent Newcastle disease, and highly pathogenic avian influenza. Urticaria and endocarditis may be caused by other bacterial or fungal pathogens. Noninfectious differential diagnoses include poisoning and physical trauma.
Treatment, Control, and Prevention of Erysipelas in Poultry
Short-acting penicillin
Vaccination
Treatment
The antimicrobial of choice to treat erysipelas is a short-acting penicillin such as potassium or sodium penicillin G. For individual birds, penicillin G (22,000 IU/kg, IM, every 24 hours for 5 days) may be administered. In situations in which it is impractical to handle every bird, administration of penicillin in drinking water (395,000 IU/L, PO, for 4–5 days) decreases losses.
Antimicrobials can be administered simultaneously with a full dose of erysipelas bacterin (but not with live vaccines); however, the onset of immunization can be several weeks after vaccination. Injectable penicillin can be administered in an acute outbreak but may be an extra-label use in many countries. Antimicrobials should be used under veterinary supervision, and regulatory guidelines for the use of antimicrobials must be considered in food animals.
Sulfonamides and oral oxytetracycline are usually less effective than short-acting penicillin; broad-spectrum antimicrobials such as amoxicillin may be effective but may represent extra-label use. Resistance to tetracycline has been reported.
If readily available, antimicrobial susceptibility testing can be useful in treatment selection. Antimicrobials in feed or water treat only those in the flock that are still eating and drinking normally and may not have dramatic results in flocks with extensive morbidity. Neither treatment with antimicrobials nor vaccination eliminates the carrier state. Recovered birds have a high level of resistance.
Prevention
Erysipelas vaccination is recommended for poultry in high-risk environments. Both inactivated and live, attenuated vaccines are available for turkeys. Erysipelas vaccines are less frequently used in chickens and other poultry species; however, in highly susceptible flocks, extra-label use of erysipelas vaccines is reported to be effective.
Vaccination with a bacterin helps protect birds in the flock not yet infected. Subcutaneous and intramuscular administration of bacterins in turkey flocks is effective but labor-intensive. For turkey breeders, at least two doses of bacterin should be given at a 2- to 4-week interval. Bacterins should be administered before onset of egg production.
Administration of live, avirulent vaccines in drinking water does not require handling each bird and, therefore, is less stressful. Live, attenuated vaccines can be efficacious in a single dose; however, in some situations, a subsequent booster may be required. Antimicrobial treatment should be discontinued 8–10 days before administration of live, attenuated vaccines.
Prevention strategies also involve biosecurity, cleaning, disinfection, and sound management practices, particularly in endemic areas. After an outbreak, equipment should be thoroughly disinfected, and dead birds should be promptly removed from the premises.
If surfaces are cleaned of debris and organic material before disinfection, the organism is destroyed by commonly used laboratory disinfectants:
1:1,000 concentration of bichloride of mercury
0.5% sodium hydroxide solution
3.5% liquid cresol
5% solution of phenol
quaternary ammonium
chlorine
0.5% formalin
E rhusiopathiae is quite resistant to desiccation and can survive smoking, pickling, and freezing. It can survive in litter or soil for prolonged periods in litter or soil. Survival in soil for up to 73 days has been reported (2). Infected carriers can shed the organism, seeding the environment and making disinfection of premises difficult.
Zoonotic Risks of Erysipelas in Poultry
E rhusiopathiae can infect humans and causes different disease presentations:
Erysipeloid is the acute, often self-limiting cutaneous form of cellulitis that is typically localized on limbs.
In rare cases, erysipeloid lesions can progress to diffuse cellulitis.
Bacterial septicemia, complicated by arthritis, lymphadenopathy, encephalitis, and endocarditis, occurs infrequently, mainly in immune-compromised hosts.
The disease is usually occupational, and those at risk include veterinarians, butchers, and fish handlers who may handle infected tissues. The organism usually enters through cuts in skin. There have been no reports of humans becoming infected through the oral route.
Key Points
Erysipelothrix rhusiopathiae has a wide host range and can infect many domestic and wild avian species. In poultry, erysipelas is most economically important in turkeys. Recently, there is an increased incidence of this disease in laying hens.
All ages are susceptible, but disease most often occurs in mature poultry.
The predominant clinical sign is sudden death, sometimes preceded by decreased egg production and water consumption. Severe lethargy, cutaneous lesions, and swollen hocks can sometimes occur.
Presumptive diagnosis is based on gross lesions and impression smears of fresh spleen or liver; definitive diagnosis is usually by aerobic culture or PCR assay.
The treatment of choice is short-acting penicillin and vaccination.
Erysipelas is zoonotic.
For More Information
Logue CM, Andreasen CB, Borst LB, et al. Other bacterial diseases. In Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020:995-1085.
Kariyawasam S. Erysipelothrix rhusiopathiae. In Williams SM, ed. Dufour-Zavala L, Jackwood MW, Lee MD, et al, associate eds. A Laboratory Manual for the Isolation and Identification of Avian Pathogens. 6th ed. American Association of Avian Pathologists; 2016:45-48.
Opriessnig T, Forde T, Shimoji Y. Erysipelothrix spp.: past, present, and future directions in vaccine research. Front Vet Sci. 2020;7:174.
Abd El-Ghany W. A review article on avian erysipelas infection: an occupational disease of one health importance. Vet Integrative Sci. 2023;21(2):481-494.
References
Eriksson H, Nyman AK, Fellström C, Wallgren P. Erysipelas in laying hens is associated with housing system. Vet Rec. 2013;173(1):18. doi:10.1136/vr.101388
Wood RL. Survival of Erysipelothrix rhusiopathiae in soil under various environmental conditions. Cornell Vet. 1973;63(3):390-410.
