JPC SYSTEMIC PATHOLOGY

REPRODUCTIVE SYSTEM

JANUARY 2025

R-B08

 

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, cotyledon and intercotyledonary area: Within the cotyledon, there is multifocal to coalescing loss of chorionic villar architecture with replacement by abundant eosinophilic cellular and karyorrhectic debris (lytic necrosis), hemorrhage, fibrin, edema, and viable and necrotic neutrophils with fewer macrophages and foci of intensely basophilic granular, angular mineral that multifocally expands the intervillous space. Scattered throughout the necrotic debris, the cytoplasm of intact and sloughed trophoblasts is often markedly expanded by amphophilic to pale basophilic, homogenous inclusions composed of innumerable <1 µm cocci occasionally admixed with scant mineral. Within the chorioallantoic connective tissue, the tunica intima and tunica media of multifocal blood vessels are infiltrated and expanded by neutrophils admixed with eosinophilic karyorrhectic debris and scant fibrin (necrotizing vasculitis). Multifocal vascular lumens are 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 (edema) and ectatic lymphatics. The intercotyledonary chorionic epithelium is either ulcerated or lined by degenerate or necrotic trophoblasts that occasionally contain previously described intracytoplasmic inclusions of <1µm cocci. The surface and underling stroma contain variable amounts of necrotic debris and mineral admixed with neutrophils, lymphocytes, and plasma cells. 

 

MORPHOLOGIC DIAGNOSIS: Chorioallantois, cotyledon and intercotyledonary area: Placentitis, necrosuppurative, diffuse, severe, with vasculitis and intratrophoblastic inclusions of cocci, cross-bred sheep, ovine.

 

ETIOLOGIC DIAGNOSIS: Placental chlamydiosis

 

CAUSE: Chlamydia abortus (formerly Chlamydophila abortus)

 

CONDITION: Ovine enzootic abortion or Enzootic abortion of ewes (EAE)

 

GENERAL DISCUSSION:

• 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
• Zoonotic and reportable - may cause abortion in women in close contact with aborting ruminants
• Unique morphology and biphasic life cycle with four morphologically distinct forms

• Elementary body (EB): Extracellular and infectious form of bacteria that enters the cell; (0.2 µm)
• Reticulate body (RB): Intracellular, metabolically active, noninfectious, replicating form that synthesizes DNA, RNA, and protein, and divides by binary fission (0.8 µm)
• Intermediate body (IB): Morphologic characteristics between EB and RB
• Persistent aberrant body (PAB): Non-replicating bodies emerge during times of stress (i.e. antibiotics), revert to RB when stressor removed; associated with long-term infection

 

PATHOGENESIS:

• Ingestion of infective placenta or uterine discharge (also vaginal discharge and semen) from aborting ewes > oral, conjunctival, or reproductive mucosae exposure > bacteremia > latent infection at an unknown site in body 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 > bacteremia > 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 (up to 75%) when newly introduced to a flock; once enzootic in a flock, yearly abortion rates of 5%; 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) 
• Ewes that abort will not abort again but will carry the organism for several years
• 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 (R-B03)): Affects cotyledons and intercotyledonary areas
  • 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; hemorrhage of the subcutis, thymus, lymph nodes, muscle, thoracic and abdominal cavities; hepatomegaly

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Definitive diagnosis of Chlamydiosis can only be made histologically if intracellular Chlamydia is identified in the tissue
• 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 Chlamydia 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
• Fetus:
  • Liver/spleen: Foci of coagulative necrosis surrounded by mononuclear cells
  • Lung: Alveolar septa thickened by mononuclear cells
  • Brain: Mild meningoencephalitis with vasculitis and hemorrhage

 

ULTRASTRUCTURAL FINDINGS:

• Elementary body (EB): Spherical, 0.2-0.3 µm body composed of a highly electron dense nucleoid at the periphery, clearly separated from the electron dense cytoplasm
• Reticulate body (RB): 0.5-2.0 µm, binary fission characterized by “hour-glass” profiles
• Intermediate body (IB): 0.3-1.0 µm diameter bodies with a central electron dense core, radially arranged nucleoid fibers surrounding the core, and tightly packed cytoplasmic granules at the periphery
• Persistent aberrant body (PAB): Small, inhomogeneous reticulate bodies 
• 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 – may be easier to find organisms on cytology of fresh tissue (liver, spleen, or air sacs) versus histology - small, 0.5 μm, intracellular organisms in macrophages and/or hepatocytes
• Fluorescent antibody test, ELISA, PCR and/or DNA sequencing of chlamydial 16s RNA and ompA genes, immunoperoxidase procedure
• Demonstration of antibodies in the dam is of little use as a large proportion of cattle and sheep have been exposed and test positive
• Can be grown in Vero cells, but may take several days before the organism can be detected.
• Electron microscopy (EM)

 

DIFFERENTIAL DIAGNOSIS:

• Chlamydia pecorum: Similar lesions to C. abortus; differentiate by cell culture isolation and PCR
• 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 ssp. 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 Campylobacter spp.
• Coxiella burnetii (R-B07): 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 C. 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

 

COMPARATIVE PATHOLOGY:

Chlamydia sp. in other species:

• Ruminants 

• C. abortus: Sporadic bovine encephalomyelitis, pneumonia, polyarthritis of calves, conjunctivitis, and sporadic abortions; reported to cause bronchopneumonia in experimentally challenged calves

• Can cause infectious keratoconjunctivitis (IKC) in bighorn sheep in North America; lesions are similar to those seen in mycoplasma-associated IKC (keratitis with mononuclear to neutrophilic, limbic and corneal infiltrates, edema, and neovascularization accompanied by conjunctival lymphofollicular hyperplasia; corneal lesions can progress to perforation in advanced cases with anterior synechiae and staphyloma formation; corneal fibrosis seen in survivors; death during outbreaks of IKC is usually secondary to blindness with lesions of trauma, predation, or emaciation)

• C. pecorum:

• Enteritis in calves <10 days old
• Meningoencephalitis, vasculitis, and abortion in cattle (Struthers, Vet Pathol. 2021) (see N-B05 for encephalitis manifestations of sporadic bovine encephalomyelitis)
• Arthritis in sheep (Ostfeld, Vet Pathol. 2021)
• Aporadic ovine abortions (Westermann, Vet Pathol. 2021) 

• C. psittaci
• C. suis

• Camelids: C. abortus: possible cause of ovarian hydrobursitis; 86% camels have serologic evidence of infection, suggesting organism involved in pathogenesis
• Horses 

• C. abortus, C. pneumonia: Equine pneumonia or abortion - C. abortus may be a more prevalent cause of conception failure and abortion in horses in western Canada, and stronger biosecurity protocols may be warranted. (Ricard, J Vet Diagn Invest, 2023 and 2024) 
• C. psittaci: Identified in cases of abortion, premature death of foals in Australia, one case in Switzerland (Bauman, J Vet Diagn Invest. 2020)

• Avians 
• C. psittaci (D-B12, psittacosis): Most commonly C. psittaci genotype B; more than 465 avian species affected; 

• Pigeons and psittacines, especially young birds, most commonly affected; adults can be carriers; subclinical infections are common, especially in cockatiels; New World parrots often get severe disseminated disease 
• Organisms propagate in epithelial cells of the respiratory tract and then spread to other organs

• Clinical signs: Sinusitis, dyspnea, conjunctivitis, polyuria, diarrhea, lethargy, anorexia, yellow to dark green droppings, poor feathering, flaccid paralysis of the legs, chronic weight

• Rare in Galliformes, but turkeys most commonly affected within this group
• Infrequently described in birds of prey despite high prevalence of antibodies to C. psittaci
• Multifocal hepatic necrosis, splenomegaly, and fibrinous airsacculitis, pericarditis, and peritonitis; can cause orchitis and epididymitis in systemic infection of turkeys and companion birds

• Most consistent lesion is systemic histiocytic inflammation

• Zoonotic infections range from asymptomatic to severe systemic disease with pneumonia, myocarditis, and encephalitis (reportable disease)

• C. gallinacea: Detected in domestic poultry, guinea fowl, turkeys, ducks, and wild birds; common in clinically healthy chickens; no overt disease in chickens but associated with significant body weight reduction; thought to be endemic in chickens with ability to persist over time; zoonotic potential 
• C. avium: Found in pigeons and psittacines in European countries; limited data linking to respiratory disease in these species
• C. trachomatis 
• C. pecorum

• Koalas 

• C. pecorum: Most common infectious disease of koalas; transmitted sexually, during parturition, or by ingestion of maternal feces by young; causes keratoconjunctivitis (can progress to blindness), vaginitis, ovarian cysts, infertility; urogenital disease ("wet tail" or "dirty tail"), pyometra, metritis, cystitis +/- ascending pyelonephritis; prostatitis, orchitis; associated with herpesvirus shedding (possible concomitant transmission, but unclear)

• Histologically, associated with lymphoplasmacytic inflammation and is most severe in lamina propria-superficial submucosa; chronic cases can have extensive fibrosis 

• C. pneumoniae: rhinitis, pneumonia, conjunctivitis

• Pigs (C. suis, C. abortus, C. pecorum, and C. psittaci)

• C. abortus: abortion, vaginitis, endometritis, seminal vesiculitis, mastitis (latent)
• C. pecorum: polyarthritis, serositis, enteritis, pneumonia
• C. suis: Conjunctivitis, pneumonia, enteritis, polyarthritis

• Cats 

• C. felis: persistent conjunctivitis 
• C. psittaci: one case of fatal infection in kitten (Sanderson, J Vet Diagn Invest. 2021)

• Guinea pigs: C. caviae: Guinea Pig Inclusion Conjunctivitis (GPIC); can also cause rhinitis and genital tract infections
• Mice and hamsters: C. muridarum: pneumonitis, ileitis
• Reptiles: C. psittaci and C. pneumoniae (more common); free-ranging and captive reptilian hosts including puff adders, boas, chameleons, crocodiles, turtles, and tortoises; granulomatous inflammation in inner organs such as heart, liver, spleen and lung; causes cutaneous hyperemia, excessive shedding of skin (sloughing), subcutaneous edema and hepatosplenomegaly

• Free-ranging giant barred frog from Australia: Predominant lesion is mononuclear interstitial pneumonia
• Captive Houston toads: Encephalitis common

• Humans:

• C. pneumoniae: Respiratory infections; nearly ubiquitous in humans, with seropositivity rates of 70–80% in older populations
• C. trachomatis: Ocular (inclusion conjunctivitis in newborns) and genital infections; infantile pneumonia
• C. abortus: Abortion in pregnant women following contact with aborting/lambing sheep and goats; if untreated, may progress to life-threatening illness
• C. psittaci: Influenza-like symptoms; pneumonia
• C. muridarum

 

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