Signalment:  

Adult, female, crossbred, domestic swine (Sus scrofa domestic).During the last 2 years, an increased abortion rate was observed in several holdings with free-range pigs in Mecklenburg-Western-Pomerania, as in this case.


Gross Description:  

Randomly distributed within the endometrium, slightly elevating the edematous mucosa, numerous small, sharply demarcated grey-yellow nodules were present. The nodules were firm and gritty when cut. Few of these granulomas gleamed through the uterus wall and were also visible in the perimetrium.


Histopathologic Description:

Uterus: Multifocally within the severely edematous endometrium and submucosa there are large, up to 3 mm diameter, sharply demarcated areas of caseous necrosis surrounded by numerous histiocytes, epithelioid macrophages, large numbers of lymphocytes and few neutrophils. A pronounced infiltration with lymphocytes is observed in the subjacent and perivascular connective tissue, predominantly surrounding endometrial glands. Myriad coccobacilli are occasionally present within the necrotic centers of the granulomas (not visible in all sections).


Morphologic Diagnosis:  

Uterus: Endometritis, mild to moderate, granulomatous and necrotizing, domestic swine, Sus scrofa domestica, etiologic diagnosis consistent with miliary brucellosis


Lab Results:  

Microbiology revealed a moderate growth of small colonies suspicious for Brucella spp. By PCR of endometrial tissue samples, DNA specific for Brucella sues, biovar 2 was amplified.


Condition:  

Brucella suis


Contributor Comment:  

Brucellosis is a zoonotic disease which is caused by gram-negative, strictly aerobic, nonmotile coccobaccilli. These are facultative intracellular microbes taxonomically categorized in the class alphaproteobacteria, family Brucellaceae.(4) Nine different Brucella species are known, but only seven of them infect terrestrial animals, namely B. melitensis, B. abortuts, B. suis, B. canis, B. ovis, B. neotomae, and B. microti. In contrast, B. ceti and B. pinnipedialis are confined to marine mammals. Each Brucella species can further be classified in several biovars.(3)

Brucellosis is endemic in Mediterranean countries, Africa, India, Asia, the Middle East and Central and South America.(4) The only known focus of Brucella abortus infection left in the United States is in bison and elk in the Greater Yellowstone Area, including Yellowstone National Park.

Five biovars have been described for B. suis, the cause of porcine brucellosis. Swine are mainly affected by biovars 1, 2 and 3. Hares are the important natural reservoir of biovar 2. Furthermore, pigs are susceptible to infection with B. melitensis as well as B. abortus.(1) Besides pigs, several species can be affected by different biovars of B. suis including reindeer, caribou and rarely, cattle and dogs. Additionally, all biovars of B. suis can induce serious infections in man,(4) in particular biovars 1 and 3.

Brucella suis affects pigs of all ages and breeds. Infection occurs through inhalation or ingestion of organisms. High numbers of bacteria are shed in urine, vaginal discharges, semen and the products of birth.(4) Venereal transmission is also possible.(1) The infectious agents invade the mucosa and gain entry into regional lymph nodes. The incubation period ranges from 2 weeks up to 7 months. Subsequently most animals develop bacteremia that results in dissemination to the spleen, liver, and bone marrow, as well as mammary glands and reproductive organs. However, a self-limiting infection which is restricted to lymph nodes only may also occur in piglets.(4)

Signs of disease in sows include infertility, abortion between weeks 4 and 12 of gestation, stillbirths, mummification, or birth of weak piglets. Abortions due to Brucella spp. are typically associated with placentitis. The gross examination of the placenta may reveal red, yellow, normal or necrotic cotyledons. A leathery, wet appearance of the intercotyledonary region with focal thickening is typical in cattle as well as sheep and goat.(5) In boars, the most prominent clinical sign is unilateral orchitis. Other signs are infertility, lameness and paralysis.(4)

A characteristic image is seen in hares infected with B. suis biovar 2. While the hares body condition may be unaltered, a widespread distribution of nodular suppurative inflammation can be seen. In particular the reproductive organs, but also the spleen, liver and lung are affected.

Brucellosis can be diagnosed by culture, serology or molecular based techniques. In most cases, serological tests are applied, although they are not completely specific. In this regard it has to be emphasized that in any case a reaction due to B. melitensis cannot be distinguished from cross-reactions to other bacteria, in particular Yersinia enterocolitica O:9 (USDA). Further techniques which are available for most species include immunostaining of tissue samples as well the polymerase chain reaction (PCR).

In 2008, five outbreaks of brucellosis were reported in Mecklenburg-Western-Pomerania a Federal State in the northeast of Germany. Three of these outbreaks were caused by B. suis biovar 2. Like the situation in other European countries, B. suis is hypothesized to be locally endemic in wild boars, and this seems to be the source of transmission of B. suis biovar 2 introduction to free-range pig holdings.


JPC Diagnosis:  

Uterus: Endometritis, lymphoplasmacytic, diffuse, severe with diffuse, marked edema, multiple pyogranulomas, and epithelial hyperplasia, degeneration and necrosis.


Conference Comment:  

When histologically assessing the endometrium, the moderator commented there are 7 structures to evaluate.
  1. Lumen: Examine for the presence of exudate; the lack of observation of an exudate histologically does not mean there is an absence of exudates, as it can be lost during fixation and processing
  2. Epithelium: There should be a single layer of mucosal epithelium
  3. Stratum compactum
  4. Endometrial glands: Glands will be hyperplastic and hypertrophied during estrous. The glandular lumina contain sloughed epithelial cells often mistaken for neutrophils.
  5. Endometrial stroma: Edema indicates inflammation or estrous and is often referred to as the stratum spongiosum.
  6. Blood vessels: Medium sized arterioles may have hyalinized walls. Animals with multiple pregnancies may have prominent vessels in the endometrium.
  7. Lymphatics

Several participants commented on the presence of endometrial glands within the muscular wall of the uterus; discussion of whether or not to diagnose this as adenomyosis followed. Adenomyosis is used when there are endometrial glands and stroma between the smooth muscle bundles.(2) Adenomyosis is occasionally due to congenity malformations within the uterus. Additionally, adenomyosis may result from hyperplastic overgrowth of the endometrium.(2) The moderator commented that in this case adenomyosis is not present as the lesion most likely resulted from smooth muscle contraction in response the inflammatory milieu of cytokines which then physically forced the endometrial glands into the superficial muscular layer.

Conference participants spent some time reviewing the differential diagnosis for intracytoplasmic microbes within trophoblasts in different veterinary species.(2) The following brief list generated by participants is not intended to be all-inclusive.
The contributor provides an excellent review of porcine brucellosis.


References:

1. Anonymous. Porcine Brucellosis. In: OIE Terrestrial Manual. World Health Organization, 2009;1-7.

2. Schlafer DH, Miller RB. Female genital system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed. Vol. 3. St. Louis, MO: Elsevier Saunders; 2007:464-465,484-518.

3. Seleem MN, Boyle SM, Sriranganathan N. Brucellosis: a re-emerging zoonosis. Vet Microbiol. 2010;140:392-398.

4. Songer JG, Post KW. The genus brucella. In: Songer JG and Post KW, eds. Veterinary Microbiology, Bacterial and Fungal Agents of Animal Disease. St. Louis, MO: Saunders; 2004:200-207.

5. Spickler AR, Roth JA. Brucellosis. In: Emerging and Exotic Diseases of Animals Textbook. Ames, IA: Iowa State Press; 2006:141-143. http://www.cfsph.iastate.edu/Factsheets/pdfs/brucellosis.pdf.



Click the slide to view.


| Back | VP Home | Contact Us |