Adult castrated male horse, (Equus caballus).During quarantine, five horses imported from New Zealand to Taiwan exhibited depression, anorexia and dyspnea with elevated body temperature (40.2-40.5oC) on day one after arrival. They were treated with antibiotics and supportive therapy; however, one was found dead three days later.

Gross Description:  

The horse shows poor body condition with moderate dehydration. The thoracic cavity is filled with turbid, serosanguineous and fibrinous pleural effusion, with marked thickened attachments between the parietal and visceral pleura. Many yellowish nodules, 0.3 to 10 cm in diameter, are scattered around the parenchyma of the lung. The tracheobronchial lymph nodes and spleen are moderately enlarged. 

Histopathologic Description:

A dense band of degenerate neutrophils admixed with bacterial colonies and fibrinous exudates covers the visceral pleura. The subpleura contains many well-vascularized, congested vessels and organized loose fibrous connective tissue underlain by inflammatory cells. The subpleural areas are filled with viable and degenerate plasma cells, epithelioid macrophages, fewer multinuclear giant cells and lymphocytes. There is diffuse intra-alveolar and interlobular edema and congestion. Alveolar septa are congested. Some sections of lung contain large areas of abscessation (not provided). These foci contain sheets of degenerate neutrophils admixed with fewer macrophages, necrotic debris, and colonies of cocci. 

Morphologic Diagnosis:  

1. Lung: Pleuritis, fibrinopurulent, diffuse, severe, subacute to chronic, with intralesional cocci colonies.
2. Lung: Abscesses, multifocal, moderate, subacute, with intralesional cocci.

Lab Results:  

Streptococcus equi subsp. zooepidemicus was identified from thoracic fluid, lung and spleen.


Streptococcus equi subsp. zooepidemicus

Contributor Comment:  

Streptococcus equip subsp. zooepidemicus is a beta-hemolytic gram-positive cocci that belongs to the Lancefield group C of streptococci and causes disease in a variety of mammals.(1,2,6) It consists of 3 subspecies, S. equip subsp. equi, S. equip subsp. zooepidemicus, and S. equip subsp. ruminatorum. 

Transmission is mainly via aerosol, wound contamination, oral or contagious route.(2) Aerosol transmission is the most likely route in this case. S. equi subsp. zooepidemicus is considered to be an opportunistic pathogen in horses and alpaca; it is commonly found in the nasopharynx of clinically normal horses.(1,6) There are reports of sporadic or outbreaks in many species, including humans. S. equi subsp. zooepidemicus has been associated with mastitis,(12) abscesses, meningitis, endocarditis, reproductive system disease, orchitis, arthritis, septicemia and respiratory and uterine infections.(1,3,7) Human infections caused by S. equi subsp. zooepidemicus include outbreaks of foodborne illness, meningitis, septicemia, arthritis, pneumonia, glomerulonephritis, and streptococcal toxic shock syndrome, in both immunocompromised and immunocompetent patients.(3) Severe S. equi subsp. zooepidemicus induced pleuropneumonia has been observed in horses. In Peru, infection can cause a mortality rate of 50-100% of affected alpacas (known as alpaca fever).(4,6) In China, S. equi subsp. zooepidemicus is the most commonly isolated secondary pathogen in swine since 1975. Humans may be infected via contact with sick animals, unpasteurized milk or other dairy products;(12) therefore, this bacterium poses a zoonotic health risk to animals and humans. 

Since 2004, this pathogen has been isolated from three batches of horses imported (from the United States and New Zealand) to Taiwan. The source of infection in the present cases is presumably associated with transport stress. There have been no reports of S. equi subsp. zooepidemicus infection in livestock, zoo/wild animals or pets in Taiwan prior to this report. 

JPC Diagnosis:  

Lung: Pleuritis, fibrinosuppurative, chronic, diffuse, severe, with granulation tissue, mild fibrinous interstitial pneumonia and rare colonies of cocci.

Conference Comment:  

Conference participants are urged to review WSC 2013-2014, conference 5, case 1 for a detailed review of various Streptococcus species important in veterinary medicine. S. equi subsp. equi is the causative agent of strangles, a contagious infection of the equine upper respiratory tract and local lymph nodes with occasional hematogenous dissemination to internal organs (bastard strangles). Bronchopneumonia (due to aspiration of nasopharyngeal exudate), guttural pouch empyema, laryngeal hemiplegia (roaring due to recurrent laryngeal nerve compression from retropharyngeal lymphadenopathy) and facial paralysis/Horner syndrome (secondary to compression of adjacent sympathetic nerves) are common sequelae to strangles. S. equi has also been linked with immune-mediated vasculitis and purpura hemorrhagica in horses. S. equi, unlike S. equi subs. zooepidemicus, is not part of the normal nasal flora.(8,9,13) S. zooepidemicus is associated with reproductive disease and bursitis (or fistulous withers) in horses,(12) as well as cervical lymphadenitis (or lumps) in guinea pigs.(10) It was also implicated in an outbreak of acute hemorrhagic pneumonia in more than 1,000 shelter dogs in California(11) and has been associated with increased severity of clinical signs in dogs affected by the canine infectious respiratory disease complex, which likely involves challenge with both bacterial (Bordetella bronchiseptica, Pasturella spp., Mycoplasma spp., S. zooepidemicus) and viral (canine parainfluenzavirus and canine adenovirus) agents.(3) S. equi subsp. ruminatorum has been associated with mastitis in domestic sheep and goats, as well as abscesses (similar to strangles) with subsequent pneumonia in spotted hyenas and zebras.(5)


1. Abbott Y, Khan S, Muldoon EG, Markey BK, Pinilla M, Leonard FC, et al. Zoonotic transmission of Streptococcus equi subsp. zooepidemicus from a dog to a handler. J Med Microbiol. 2010;59:120-123.

2. Brack M, G+�-+nther E, Gilhaus H, Salzert W, Meuthen J. An outbreak of Streptococcus equi subsp. zooepidemicus infection of probable human origin in Wanderoos (Macaca silenus)--case report. Zentralbl Bakteriol. 1997;286:441-446.

3. Chalker VJ, Brooks HW, Brownlie J. The association of Streptococcus equi subsp. zooepidemicus with canine infectious respiratory disease. Vet Microbiol. 2003;95:149-156.

4. Hewson J, Cebra CK. Peritonitis in a llama caused by Streptococcus equi subsp. zooepidemicus. Can Vet J. 2001;42:465-467.

5. Honer OP, Wachter B, Speck S, et al. Severe Streptococcus infection in spotted hyenas in the Ngorongoro Crater, Tanzania. Vet Microbiol. 2006;115:223-228.

6. Jones M, Miesner M, Grondin T. Outbreak of Streptococcus equi susp. zooepidemicus polyserositis in an alpaca herd. J Vet Intern Med. 2009;23: 220-223.

7. Lamm CG, Ferguson AC, Lehenbauer TW, Love BC. Streptococcal infection in dogs: A retrospective study of 393 cases. Vet Pathol. 2010;47:387-95.

8. Lopez A. Respiratory system, mediastinum and pleurae. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 5th ed. St. Louis, MO: Mosby Elsevier; 2012:470. 

9. Maxie MG, Youssef S. Nervous system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed. Vol. 1. Philadelphia, PA: Elsevier; 2007:173, 257, 358.

10. Percy DH, Barthold SW. Pathology of Laboratory Rodents and Rabbits. Ames, IA: Blackwell Publishing; 2007:229-232. 

11. Pesavento PA, Hurley KF, Bannasch MJ, Artiushin S, Timoney JF. A clonal outbreak of acute fatal hemorrhagic pneumonia in intensively housed (shelter) dogs caused by Streptococcus equi subsp. zooepidemicus. Vet Pathol. 2008;45(1):51-53. 

12. Pisoni G, Zadoks RN, Vimercati C, Locatelli C, Zanoni MG, Moroni P. Epidemiological investigation of Streptococcus equi subspecies zooepidemicus involved in clinical mastitis in dairy goats. J Dairy Sci. 2009;92:943-951.

13. Timoney, JF. The pathogenic equine streptococci. Vet Res. 2004;35(4):397-409.

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1-1. Lung

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1-5. Lung

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