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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


Diseases causing Abortion