JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2015774): A cross-bred ewe
HISTORY: A flock of cross-bred ewes experienced an abortion outbreak with 40% of the ewes affected. The aborted fetuses were near-term and in a fresh state.
HISTOPATHOLOGIC DESCRIPTION: Chorioallantois: There is diffuse loss of chorionic villar architecture with replacement by abundant eosinophilic cellular and karyorrhectic debris (necrosis), hemorrhage and viable and degenerate neutrophils with fewer macrophages and concretions of intensely basophilic granular material (mineral), which expands the intervillous space. Still attached and sloughed trophoblasts, scattered throughout the necrotic debris are often markedly expanded by numerous indistinct intracytoplasmic, amphophilic, 1 um diameter cocci admixed with small amounts mineral. Multifocally within the chorioallantoic connective tissue, blood vessel walls are infiltrated by eosinophilic karyorrhectic debris, neutrophils and scant amounts of fibrin which expand the tunica intima and media (necrotizing vasculitis). Vascular lumens are multifocally variably occluded by fibrin thrombi. There are perivascular accumulations of viable and degenerate neutrophils with fewer macrophages, lymphocytes and plasma cells. Within the chorioallantoic stroma there are low numbers of previously described inflammatory cells as well as increased clear space and dilated lymphatics (edema). The intercotyledonary chorion is ulcerated or lined by epithelium that is degenerate or necrotic, with epithelial cells occasionally containing amphophilic, 1 um diameter cocci. The surface and underling stroma contain variable amounts of necrotic debris and mineral admixed with neutrophils, lymphocytes and plasma cells.
MORPHOLOGIC DIAGNOSIS: Chorioallantois: Placentitis, necrosuppurative, diffuse, severe, with vasculitis, and intratrophoblastic cocci, consistent with Chlamydia abortus, cross-bred sheep, ovine.
ETIOLOGIC DIAGNOSIS: Placental chlamydophilosis
CAUSE: Chlamydophila abortus
CONDITION: Ovine enzootic abortion or Enzootic abortion of ewes (EAE)
- Contagious disease with worldwide distribution that causes fever, abortion, stillbirths and birth of weak lambs
- Gram-negative, obligate intracellular bacterium; forms a cell wall; multiplies in membrane-bound vacuoles; larger than viruses; possess DNA and RNA
- Does not synthesize ATP like bacteria; susceptible to antibiotics
- Chlamydophila has two morphological forms and an intermediate form:
- Elementary bodies are the mature, infectious form
- Intermediate bodies are a transition stage between elementary and reticulate bodies
- Reticulate bodies are the metabolically active, noninfectious replicating form that forms microcolonies within intracellular chlamydial inclusion bodies
- Transmission via ingestion of infective placenta or uterine discharge (also vaginal discharge and semen) from aborting ewes -> latent infection, maintained under the control of IFN-gamma (induces production of indoleamine 2,3-dioxygenase which makes tryptophan unavailable to the organism and induces production of nitric oxide that directly inhibits the organism) -> release from latency during pregnancy due to immune modulation -> chlamydophilemia -> hematogenous spread to the placenta -> organisms transverse maternal capillaries and enter the extravasated blood in the lacunae -> infect trophoblasts and replicate within chlamydial inclusions -> host cell bursts and infects neighboring cells ->organism enters the fetus at the site of placental damage -> abortion occurs secondary to fetal death, resulting from damage to the pregnant uterus, placenta and/or fetus (production of TNF-alpha by fetal macrophages expressing MHC II molecules)
- Chlamydiae use major outer membrane proteins, heat shock protein 70, OmcB, and heparin sulfate-like glycosaminoglycans as adhesins -> concentrate on specialized membrane microdomains rich in cholesterol, glycosphingolipid, and caveolin on host cell surfaces ->polymorphic membrane proteins involved in early entry -> host cell cytoskeleton rearrangement leads to bacterial uptake in a chlamydial inclusion, the membrane of which has clatharin coated pits -> organism replicates within the inclusion -> Type III secretion system to secrete proteins in the inclusion membrane
TYPICAL CLINICAL FINDINGS:
- Abortions occur in outbreaks (when newly introduced to a flock) or enzootically; incubation is 50-90 days
- Infected ewes: Little to no clinical signs of disease after infection until they abort
- Ewes infected before 5-6 weeks of gestation -> abort in late gestation (or have still birth or weak lamb)
- Ewes infected after 5-6 weeks of gestation -> abort in subsequent pregnancy
- Abortion occurs during the final trimester (late term)
- Lambs may be still born or weak at birth
- Ewes may be sick, retain fetal membranes or develop metritis
TYPICAL GROSS FINDINGS:
- Placenta (similar to bovine brucellosis): affects cotyledons and intercotyledonary
- Cotyledons dull-clay or dark-red color, firm, and matted with a dirty-red exudate;
- Intercotyledonary areas are red to brown, irregular patches of edema amidst a dry, leathery thickening of the chorioallantois
- Fetus: usually well preserved, few gross lesions; subcutis hemorrhage, thymus, lymph nodes, muscle, thoracic and abdominal cavities; hepatomegaly
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Placenta: Necrotizing placentitis, organisms within trophoblasts (inclusion bodies)
- Cotyledon and intercotyledonary areas: Infiltrate of neutrophils and macrophages, fewer lymphocytes with inclusions (aggregates of Gram negative Chlamydophila cells within cytoplasmic vacuole) within trophoblasts
- Endometrium: High numbers of lymphocytes
- Blood vessels: Marked vasculitis; fibrinoid necrosis of tunica media, infiltrate of neutrophils and mononuclear cells
- Liver/spleen: Foci of coagulative necrosis surrounded by mononuclear cells
- Lung: Alveolar septa thickened by mononuclear cells
- Brain: Mild meningoencephalitis with vasculitis and hemorrhage
- Unique developmental cycle occurs entirely within an intracellular vacuole (chlamydial inclusion), characterized by 2 distinct forms and an intermediate form:
- Elementary body (no metabolic activity, does not replicate, infective form): Spherical, 0.3 um diameter, eccentric electron-dense nucleoprotein core
- Reticulate body (metabolically active, replicating form): Larger (1.0 um), with ribosomes and a lacy or reticular nucleus, +/- hourglass-shaped profiles of replicating forms
- Intermediate body: Oval to round, 0.4-0.7 um, centrally located electron-dense core and granular cytoplasm
- Chlamydial cell wall has inner and outer membranes separated by a periplasmic space but no peptidoglycan layer
- Host cell glycogen and mitochondria are closely associated with the bacteria
ADDITIONAL DIAGNOSTIC TESTS:
- Staining of cotyledonary scrapings or histologic sections with modified Ziehl-Neelsen, Gimenez, Machiavello or Giemsa
- Fluorescent antibody test, ELISA, PCR, immunoperoxidase procedure
- Chlamydophila pecorum: Similar lesions to abortus; differentiate by culture
- Brucella ovis: Edematous, opaque, leathery intercotyledonary areas and necrotic cotyledons (grossly indistinguishable from mycotic abortion or rare cases of campylobacteriosis with late term abortion); light brown exudate on chorionic surface; trophoblasts with Gram-negative coccobacilli; vasculitis of larger chorionic vessels; nonspecific fetal gross lesions (calcified plaques on hooves are found but not specific); pneumonia, lymphadenitis, interstitial nephritis and pericholangitis
- Campylobacter fetus fetus and C. jejuni: Edematous intercotyledonary areas and friable yellow cotyledons; necrotizing and suppurative placentitis most severe in chorionic villi with large dense Gram-negative bacterial emboli within chorionic capillaries; yellow hepatic foci with targetoid depressed red centers (necrotizing hepatitis) and fibrinous peritonitis in fetus
- Flexispira rappini: Similar lesions as for Campylobacter
- Coxiella burnetii: Gross and histologic lesions similar; placenta thick, leathery and covered by a thick exudate; necrotizing and suppurative placentitis primarily involving intercotyledonary areas (cotyledons more affected with abortus); fetus with mononuclear inflammation in the lung, liver and kidneys; hypertrophic trophoblasts filled with organisms visible with modified Ziehl Neelsen or Macchiavello stains; often lacks vasculitis
- Listeria monocytogenes: Necrotizing and suppurative placentitis affecting the cotyledons and intercotyledonary areas, with Gram-positive bacilli filling trophoblasts; hepatomegaly and dissociation of hepatic cords in fetus; possible sepsis and metritis in aborting ewe
- Toxoplasma gondii: Gross edema of the intercotyledonary area and 1-2 mm yellow-white sometimes gritty foci in cotyledons; trophoblast hypertrophy, hyperplasia, necrosis and mineralization with toxoplasma organisms; nonsuppurative encephalitis and necrosis with tachyzoites in heart, liver, lungs and skeletal muscle of the fetus
- The family Chlamydiaceae contains a single genus: Chlamydia, which includes 11 species:
- C. muridarum (swine)
- C. suis (swine) has also been associated with abortion
- C. trachomatis (humans)
- C. abortus (ruminant): among the most common abortifacients in sheep
- C. caviae (Guinea pig): inclusion body conjunctivitis, rhinitis, genital tract infections
- C. felis (feline)
- C. pecorum (ruminants, swine, koalas): arthritis in several domestic species; conjunctivitis and sterility in koalas; has also been associated with abortion and placentitis in small ruminants
- C. pneumoniae (human, marsupial, and amphibious origin)
- C. psittaci (avian serovar)
- C. avium
- C. gallinacea
- Swine: C. pecorum, C. suis, and C. abortus; reproductive failure and abortion
- Horses: Associated with abortion
- Goats: Disease similar to that in sheep
- C. abortus is reported to cause abortion in horse, rabbit, guinea pigs and mice
- Borel N, Polkinghorne A, Pospischil A. A review on Chlamydial diseases in animals: still a challenge for Pathologists?. Vet Pathol. 2018; 55(3):374-390.
- Buxton D, Anderson IE, Longbottom D, Livingston M, Wattegedera S, Entrican G. Ovine chlamydial abortion: characterization of the inflammatory immune response in placental tissues. J Comp Pathol 2002;127:133-141.
- Giannitti F, Anderson M, Miller M, et al. Chlamydia pecorum: fetal and placental lesions in sporadic caprine abortion. J Vet Diagn Invest. 2016; 28(2): 184-9.
- Gutierrez J, O’Donovan J, Proctor A, et al. Application of quantitative real-time polymerase chain reaction for the diagnosis of toxoplasmosis and enzootic abortion of ewes. J Vet Diag Invest. 2012;24(5):846-854.
- Hazlett MJ, McDowall R, DeLay J, et al. A prospective study of sheep and goat abortion using real-time polymerase chain reaction and cut point estimation shows Coxiella burnetiiand Chlamydophila abortus infection concurrently with other major pathogens. J Vet Diag Invest. 2013;25(3):359-368.
- Longbottom D, Livingstone M, Maley S, van der Zon A, Rocchi M. Intranasal infection with Chlamydia abortus induces dose-dependent latency and abortion in sheep. PLoS ONE. 2013; 8(2) e57950.
- Lopez A, Martinson SA. Respiratory system, mediastinum, and pleurae. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:552.
- Martinez CM, Buendia AJ, Sanchez J, Ortega N, Caro MR, Gallego MC, Navarro JA, Cuello F, Salinas J. Relative importance of CD4+ and CD8+ T cells in the resolution of Chlamydophila abortus primary infection in mice. J Comp Pathol. 2006;134:297-307.
- Masala G, Porcu R, Daga C, Denti S. Detection of pathogens in ovine and caprine samples from Sardinia, Italy, by PCR. J Vet Diagn Invest. 2007;19:96-98.
- Navarro JA, Ortega N, Buendia AJ, Gallego MC, Martínez CM, et al. Diagnosis of placental pathogens in small ruminants by immunohistochemistry and PCR on paraffin-embedded samples. Vet Rec. 2009;165:175-178.
- Sammin DJ, Markey BK, Quinn PJ, McElroy MC, Bassett HF. Comparison of fetal and maternal inflammatory responses in the ovine placenta after experimental infection with Chlamydophila abortus. J Comp Pathol. 2006;135:83-92.
- Schlafer DH, Foster RA. The female genital system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. St Louis, MO; 2016:415-416.