Placenta The placenta, as a diverse organ, is involved with the exchange of nutrients and other substances between the fetal and maternal tissue interface. In addition to its function in protecting the developing fetus, the placenta produces enzymes, prostaglandins and cytokines necessary for the attachment and stability of the fetus, and transient hormones such as estrogen and progesterones to maintain pregnancy. Placentas are classified according to their gross and microscopic anatomy and on the basis of the degree of proximity of the fetal circulation to that of the mother (see following table). The fetus is surrounded by two sets of fetal membranes, which are separated by cavities containing defined amounts of fluid. The outer fetal membrane is the allantochorion, which is formed by fusion of the chorion and allantois. The chorion opposes the endometrium, while the allantois borders the allantoic space with its allantoic fluid. The allantoic fluid is composed of hypertonic urine and fetal excretory products. The second fetal membrane is the allantoamnion formed by the fusion of amnion and allantois. The allantoamnion envelops the fetus. The allantoamniotic space contains mucinous, amniotic fluid, which is composed of fetal urine and secretions from the fetal respiratory tract and oral cavity. The only attachment of the fetus to the fetal membrane is through the umbilicus. Both an amniotic and allantoic membrane covers the umbilical cord as it passes through the two spaces. It contains two umbilical arteries, one or two umbilical veins and the urachus. Placental classification Species
Distribution of Contact
Microscopic Classification
Mare, Sow
Diffuse
Epitheliochorial
Bitch, Queen
Zonary
Endotheliochorial
Ruminant Primates
Cotyledonary Discoid
Epitheliochorial Hemochorial
Placental Membranes Both fetal membranes are spread out, the chorioallantois with its flaky, velvety, reddened chorionic surface visible and the amnion as a thin, translucent membrane containing coiled muscular arteries. Amnion The allantoamnion is a thin, white, translucent membrane that completely envelopes the fetus and contains accentuated, coiled, muscular arteries Incidental Findings on Fetal Membranes Calcium Calcium is deposited in a rather loose network in the chorion of sheep, cattle and swine. This is a physiologic process and in cattle the calcium is present when the fetal size varies between 2.5 and 25 cm. Therefore, calcium is not present in visible quantities before 60 days but is usually present from this time until about 4 months of gestation. Distribution of calcium suggests that it is deposited along the course of capillaries. The calcium deposition is a physiologic process. It creates a depot of calcium in the chorion for the rapidly growing fetus. The fetus draws upon this deposit at the time of increasing calcium needs.
Epithelial Plaques These are present in the amnion of cattle. They consist of focal areas of squamous epithelium, which often becomes keratinized. Occasionally the epithelial plaques will become infolded and will form spherical cystic structures filled with keratinized epithelium. These sometimes become detached from the amnion during parturition. Hippomanes (Hippo =ipecac=dried roots). They constitute amorphous, rubbery masses of material, which develop from the deposition of material from allantoic fluid on a central nucleus of desquamated cell debris. They are actually allantoic calculi and are usually free floating in the cavity. Amorphous globosus Round, hard cystic structures next to the umbilical cord. They are considered incomplete twins or "teratomas". Accessory cotyledons or adventitious placentation: it is a common lesion in older cattle. In fact, it is rare to find a placenta that does not have some degree of development of adventitious placenta. However, in advanced cases when there is a very diffuse placentation, there may be pathologic significance. In some of these cases, there appears to be a tendency for this to be associated with hydrallantois. Adventitious placentation appears to be more pronounced in cows, which have had postpartum metritis. Retained Placenta: This condition occurs less commonly in the horse than in the cow. Retained placentation is associated with abnormalities of parturition such as dystocia, twin delivery abortion and cesarean section. Placental edema has been suggested for failure of microcotyledons to detach. In cattle, retention occurs in situations of hyposelenosis. Torsion A rotation of the pregnant uterus along its longitudinal axis leads to vascular compromise, devitalization of the uterine wall and fetal death. Embryonic and Fetal Death The pathology of the early conceptus is complex and focuses on chromosomal abnormalities of the zygote, transport problems through the uterine tubes and attachment or implantation problems within the endometrium due to diseases of the blastocyst or preexisting diseases of the endometrium. Early embryonic death resorption, or expulsion, may be the outcome of such conditions. The early conceptus disintegrates and a normal estrus cycle may occur. Viruses, several bacteria, mycoplasma species, fungi (Candida spp.) and drugs may cause damage to the zygote and early embryo. Mummification Fetal death has occurred in a more differentiated stage of gestation. If no bacteria are present, the fetus is maintained in the uterus where it undergoes slow decomposition and dehydration (mummification). The cervix usually remains closed. The fetus appears as a brown, dry, leathery structure. In a cow and sow, fetal mummification has been associated with some viral infections, but the condition is not necessarily indicative of any specific etiology.
Diseases Causing Abortion Abortion: It is defined as the expulsion of a dead fetus or living conceptus at any period of gestation. Dead fetuses expelled at term are called stillbirths. Viable fetuses born before expected parturition are called premature birth. Causes: I-Non-Infectious Diseases: Non-infections causes of abortions are most difficult to determine and vary between animal species. It may include: 1-Toxic a-Plant eg. (Nitrate, ergot, Lupinus). b-Anthelmintics eg. (Benzimidazoles). c-Mycotoxins eg. Aflatoxins,..
2-Hereditary eg. Protoporphyria. 3-Metabolic eg. Iodine or Vit. A deficiency and both selenium deficiency and selenium excess 4-Dystocia (any abnormalities during birth), which leads to Intra or Post-Partum death. 5-In horses, twinning, premature placental separation, placentation insufficiency, umbilical abnormalities.
II- Infectious Diseases: For the infectious process to affect the fetus, penetration of the agents through the placental membranes is necessary. The placental types encountered in specific animal species, as well as different responses of the fetus to the individual agent, need to be evaluated as well. The type of reaction to infectious agent insults is different in the fetus as compared to perinatal, postnatal and juvenile animals. Abortion ensues secondary to fetal death whether it is due to damage to the pregnant uterus, placental membranes or fetus. Hematogenous versus transcervical routes are major modalities of infection. There are three principal infectious manifestations in which abortions can be expected: a. Maternal systemic infection of the dam as with leptospirosis, salmonella septicemia or equine viral arteritis. b. Placental infections, as with brucellosis. c. Fetal infection as with herpesvirus. i-Bacterial - Induced Abortions In principle, infectious causes of abortion are more common than non-infectious. Infectious agents may contribute to up to 80% of bovine abortions, up to 60% in the horse and up to 80% small ruminants. A variety of grampositive and gram-negative bacterial species are recognized as abortifacient. Brucella, Campylobacter, Leptospira, Listeria, Salmonella, Chlamydia and others. ii-Viral Abortions Viruses may reach the fetus by one of three basic mechanisms: a-Direct infection by way of the vagina and cervix. b-Transplacental transmission from the mother to the fetus. c-Infection of the ovum (transovarian transmission). Examples of some specific viral abortion diseases: IBR, BVD, Blue tongue, RVF and Equine Viral Arteritis. iii-Protozoal Abortions: for examples: Trichomonas, Neospora, Toxoplasma, Sarcocystis. iv-Mycotic Abortions: Mycotic abortions are mainly encountered in cattle as sporadic events and are commonly caused by Aspergillus spp., Absidia spp., Mucor spp., Rhizopus spp. and Mortierrella wolffii. Abortions occur late in pregnancy and the placenta is often retained. When passed, it has a thickened, dry appearance. v-Mycoplasma, Ureaplasma and Rickettsia: For examples: Mycoplasma bovigenitalium, Coxiella burnetii (Q fever). vi- Unclassified Abortifactive Agent (Foothill Abortion): A tick-borne abortion disease of cattle.
Brucellosis Bangle’s Disease (Animals) Undulating Fever (human) Causes: B. abortus (cattle) B. melitensis and B. ovis (sheep) B. suis (swine) Pathogenesis: The infections are through the digestive tract, conjunctiva, vagina and skin or from infected bull and AI. The organism reaches the digestive mucosa then to mesenteric Lns. engulfed by macrophages, where it multiplicates migrate through LV. to thoracic duct then to the blood (bacteremia) without any clinical signs. In pregnant uteri, the organism attracted the uterus by the effect of Erythrinol substance (secreted from gravid uterus) then invaded the fetal membranes (placenta), uterine mucosa mammary gland and Lns of uterus and udder. In non-pregnant uteri (calf or heifer), the infection via milk of infected dam reached to udder and its Lns. (supramammary) and stay till pregnancy. In Bull, after bacteremia the organism localized in testes, epididymis and seminal vesicles. Campylobacteriosis (Vibriosis) Genital Form Abortion and infertility Causes: Campylobacter fetus Intestinal Form Enteritis and diarrhea Pathogenesis: In cow, through coitus (Venereal disease). In ewe, through ingestion of contaminated food. The organism reaches the capillaries between the maternal and fetal sides obstruction hypoxia and death of fetus expulsion outside (abortion). NB: The infection in cow lead to acquired resistance to reinfection (but in brucella, repeated abortions). Bovine Genital Trichomoniasis Causes: Tritrichomonas fetus Pathogenesis: The protozoan live in preputeal cavity (venereal) balanitis, seminal vesiculitis and epididymitis infected semen reach to vagina (Vaginitis) and uterus (endometritis).
Salmonellosis Causes: Salmonella abortus equi (in equine) transmitted by coitus (venereal). Salmonella abortus ovis (in sheep) transmitted by ingestion. Pathognomonic Lesions of These Diseases: Summarized in the following tables.
Low 0-30%
Low Up to 15% Low Less 5% Spora dic
High
Ingestion or through skin abrasions
After septicemia
From infected uterus
Ingestion and septicemia
Venereal (by Coitus)
Leptospirosis L. pomona
Listeriosis L. monocytogenes
Actinomyces pyogenes
Chlamydiosis Chlamydophila abortus
Bovine rhinotracheitis (IBR)
Ingestion
Low 5-20%
Venereal (by Coitus)
Campylobacteriosis (Vibriosis) Campylobacter foetus
Bovine viral diarrhea (BVD)
High
Digestive tract, Conjunctiva, skin, Vagina and AI.
Brucellosis B. abortus Contagious abortion
Spora dic
Rate
4-9 months
>2 months
Late, 6-9 months
trimester
Last
6-8 months
Late, 6 months
3-5 months
6-9 months (late)
Time
Abortion
Route of infection
Diseases
Pustular vulvovaginitis balanoposthitis Necrosis in GIT and Lymphoid tissues.
1-Focal necrosis in liver, Ln, spleen and kidneys. (IN/IB in respiratory epithelia. Congenital malformations eye and brain.
Placentitis and necrotic cotyledons. No macro lesions
None
Anasarca, lymphadenopathy, tracheal petechea
1-Cotyledons are dark red. 2-Periplacentome is thickened, opaque, yellowish pink and covered with clay colored exudate.
Septicemia and encephalitis circling disease
Necrosis and microabscess in the liver.
Endometritis and Pyometra
Septicemic lesions
1-Fetal death 2-Autolytic fetus. 3-Icterus may occur
1-Avascular placenta 2-yellowbrown cotyledons 3-Placenta is slightly inflamed and edematous. -Necrotic placentitis. -No retention
1-Fibrinous polyserositis. 2-Bronchopneumonia
Necrotic or suppurative orchitis, epididymitis, vesiculitis, pyocele Diffuse mucopurulent endometritis, vulvovaginitis
1-Serosinguinous fluid in s/c & intramuscular. 2-Bronchopneumonia and pleuritis. 3-Fibrinous exudate in B. cavity. 4-Spleen and L.n. enlarged & necrotic. 5-Omphalophelebitis, embolic nephritis 1-Reddish-brown fluid in all B. tissues and stomach. 2-Flakes of pus on peritoneum. 3-Focal necrotic hepatitis.
1-Focal necrotic placentitis. 2-Placenta is thick, edematous, dull (opaque) and leathery. 3-Necrosis of Cotyledons. 4-Retained placenta. 1-Semi-opaque, little thickening and edema. 2Petechiae (dark-red areas with radiated dark streaks 3-Not retained.
Placentitis with red-brown exudate & microabscesses of cotyledons
Cow/Bull
Fetus
Placenta
Pathognomonic Lesions
Moderate 5-30% Spora dic
Venereal (by Coitus) and AI.
Ingestion of sporulated oocysts
Trichomoniosis Tritrichomonas fetus
Toxoplasmosis T. gondii
Neosporosis Neospora caninum
Sarcosporiosis Sarcocystosis Sarcocystis spp.
Rare
Venereal
Mycplasmosis Mycoplasma bovigenitalium and Ureaplasma
Spora dic
Spora dic
Ingestion
Ingestion of feline feces
Rare
Inhalation
Aspergillosis (Mycoses)
Storm
Rate
Granular vulvovaginitis, S.vesiculitis and epididymitis Pyometra & Vaginitis Balanoposthitis None
None
Skin plaques or diffuse white areas
None
1-Emaciated or dead fetus, which coated with pus. 2- Fetal maceration and mummification 1-Enlargement of superficial L.ns. 2-serous atrophy and edema of B. fat 3-Hydrothorax, hydropericardium and ascites. (tachyzoites & cysts). 1-white foci in muscle and heart 2-Focal hepatic necrosis. 3-Tachyzoites in different fetal tissue
1-Necrotic cotyledons (yellow & soft). 2- thickened, dry appearance No gross lesions.
1-Destruction of placenta without inflammation. 2-Little edema. The placenta is thickened, edematous and the caruncles are atrophied. No gross lesions, but micro. the placenta show focal necrosis, tachyzoites and cyst.
1-Necrosis and calcification. As Neosporosis particularly in brain 2-Tachyzoites in trophoblasts
4-6 months
3–5 months
Variable
Early, 2-4 months
Variable
4-7 months
None
None
None
Necrosis in the liver, edema and hemorrhages in the wall of gallbladder.
None
Usually late
Time
Cow / Bull
Placenta
Pathognomonic Lesions Fetus
Abortion
By insects
Route of infection
Rift valley fever
Diseases
High
Low
Spora dic
Ingestion & wounds
Ingestion
Ingestion of feline feces
Listeriosis L. monocytogenes
Salmonellosis (S.abortus ovis and S.Dublin)
By blood sucking arthropods
By insects
Rift valley fever
Bluetongue / Its live Vaccination
By ticks
Coxiella burnetii Q fever: Rickettsia
Rare
Storm
Storm
High
Ingestion
Ovine Brucellosis Brucella melitensis and B. abortus
Toxoplasmosis T. gondii
Rare
Coitus from infected rams
Ovine Brucellosis (B. ovis)
High
Rate
1-Birth die or die after birth. 2-Septicemia, pneumonia and gastroenteritis.
Edema of subcutis Normal.
1-Placenta is thickened, edematous and necrotic. 2-Hematoma or hematocyst between allantoins and chorion. (Retained placenta). Multiple small necrotic foci in fetal cotyledons Placenta is thickened and the cotyledons is necrotic
Last 6 weeks
Late or stillbirth
1–2 months
Usually late
Any time
Placenta is only congested.
1-Necrotic meningoencephalitis. 2-Lungs is edematous and pneumonic.
Necrosis in the liver, edema and hemorrhages in the wall of gallbladder.
Metritis and Septicemia in some ewes circling disease
Necrosis and microabscess in the liver.
-Necrotic placentitis. -No retention
3 months
None
Endometritis
Pneumonia
As in cattle (Necrotic Placentitis)
Late
Bronchopneumonia
Fibrinous placentitis
Late or stillborn. Abortion
Not genital
Not genital
None
None
-Suppurative endometritis (No cervicitis) -Septicemia & Gastroenteritis
Orchitis and Epididymitis
Metritis in ewes after abortion.
1-Organisms in stomach. 2-Necrotic hepatitis. 3-Fibrinous peritonitis
Necrotic placentitis
2 months onwards
Ewe/Ram Severe septicemia and Metritis
Fetus 1-Chlamydia org. in fetal cotyledons. Lymphoid hyperplasia and edema in B. cavity. 2-Retained Placenta.
Placenta
Pathognomonic Lesions 1-Cotyledons are dark red. 2-Periplacentome is thickened, opaque, yellowish pink and covered with clay colored exudate.
Last 2–3 weeks
Time
Abortion
Low 5-20%
Ingestion.
Route of infection
Ingestion
Campylobacteriosis Campylobacter fetus
Enzootic abortion (Chlamydia psittaci)
Diseases
Equine Herpesvirus Abortion
Respiratory and Nurogenic disease
After Viremia
Equine Viral Arteritis
(Pink Eye)
Ingestion
Venereal
Route of infection
Brucellosis B.abortus,B.melitensis
Salmonellosis S. abortus equi
Diseases
High
Rare
Rare
High
Rate
Non-Specific
Edema and necrosis due to vasculitis.
None
Variable
9 – 10 months
1-Pulmonary edema (interlobular). 2-Necrotic foci in the liver (IN/IB). 3-Ictrus and ascites. 4-Intrauterine death.
None
7 months
8 - 11 months
As cattle
Fetus 1-Birth die or die after birth. 2-Septicemia, Pneumonia and Gastroenteritis
Placenta
Pathognomonic Lesions 1-Dark or hemorrhagic. 2-Thickened and edematous. 3-Has necrotic foci.
Time
Abortion
None
Necrotizing myometritis
Suppurative arthritis and fistulous withers
Suppurative Cervicitis, endometritis, septicemia and orchitis
Mare/Stallion