Pregnant Uterus - Infectious Pathology

INFECTIOUS DISEASES OF PREGNANT UTERUS

• Ascending infection via vagina and cervix, e.g. bacteria and fungi in mare; Campylobacter fetus ss venerealis in cows.
• Haematogenous via maternal circulation (bacteraemia/viraemia) or transplacental. Abortion may occur as a result of:

1. Endotoxins or pyrexia, e.g. Leptospira interrogans (pigs and cattle), Salmonella (cattle and sheep). There are no lesions in placenta or foetus although bacteria present.
2. Immediate placentitis, e.g. Campylobacter fetus ss fetus (cows), Listeria (sheep). Lesions present in foetus and placenta (cotyledon) abortion about 2 weeks after oral infection.
3. Delayed placentitis, e.g. Brucella abortus (cows), Chlamydia psittaci (sheep).
4. Direct damage to foetus, e.g. viruses BVD, parvovirus, IBR resulting in foetal death (also congenital abnormalities or persistent infection of neonate).

In many cases, the pathology relating to abortion is non-specific and a combination of history (i.e. stage of pregnancy, farm history, related clinical syndromes) culture, serology and virus isolation are required to determine the cause
Pathologic changes in foetus may also be non-specific, e.g. autolysis - kidneys most rapid, lungs least.
Many infectious agents can affect the uterus during pregnancy and some of these are listed in the Table.

insert table of Some of the causes of infertility, mummification, foetal death and abortion

Specific viral diseases

IBR
Caused by herpes virus 1 in cows. Results in abortion late in gestation 3-6 weeks after exposure. Abortion occurs soon after foetal death. Foetus may be autolysed. Intranuclear inclusions present in liver.
BVD
A pestivirus which may result in abortion of fresh, autolysed or mummified foetuses. Calves may also be born alive and may be weak, uncoordinated due to cerebellar hypoplasia (cerebellar hypoplasia also seen with feline panleukopenia infection).
Border disease virus
A pestivirus causing abortion often of brown, anasarcous foetus which may be mistaken for scouring if early in pregnancy (ewe barren at lambing time). Live lambs are born early “hairy shakers” small, weak, hairy lambs with skeletal abnormalities.
Porcine parvovirus
SMEDI syndrome leading to stillbirth, mummification, embryonic death or infertility.
PRRS Porcine reproductive and respiratory syndrome virus (Lelystad virus). There is abortion late in gestation with respiratory tract illness in live piglets (interstitial pneumonia).

Specific bacterial diseases

Brucella abortus
Affects cattle, transmission is by ingestion and abortion occurs in last half of pregnancy. Placenta is covered by fibrinonecrotic tissue. Foetus often shows bronchopneumonia.
Listeria
Caues abortions in cattle and sheep last third of pregnancy. Foetal membranes often retained leading to metritis. The placenta is covered by purulent exudate and there are focal pinpoint yellow lesions in foetal liver.
Campylobacter fetus or jejuni In ewes, causes abortion storms. Transmission is oral from faeces or aborted material and leads to late abortion, premature and weak lambs. See areas of focal hepatic necrosis in foetus.
Coxiella burnetti (rickettsia)
Infection by inhalation, ingestion or tick bites. Leads to late abortion or birth of weak lambs/kids. See a thickened leathery placenta covered in exudate. ZN stains can be use to demonstrate organisms.
Chlamydophila abortus
Enzootic abortion of ewes. Causes late abortion, premature lambing, retained foetal membranes. Infection is by ingestion. Immunity develops following exposure therefore abortion only in ewes not previously exposed. Aborted foetus may be oedematous with blood tinged fluid in body cavities. Cotyledons are necrotic, covered with exudate while foetal membranes may be thickened and oedematous.

Specific protozoal diseases

Toxoplasma
There is abortion late in gestation following infection with oocysts from cat faeces. Ewes are not clinically ill and the foetus has no gross lesions. Characteristically the cotyledons are bright red with multiple (1-3 mm) white/yellow foci (strawberry cotyledons).
Neospora caninum
A disease of cattle with late abortion of mummified or autolysed foetus. May also get foetal malformation, e.g. arthrogryposis.
Trichomonas foetus
A venereal infection of cattle that can cause early embryonic death and abortion.

Specific fungal diseases

Abortions due to mycotic agents affect individuals rather than causing outbreaks.
In cattle may be associated with intestinal ulcers infected with fungus and haematogenous spread to uterus.
Abortion is late in pregnancy and the placenta is often retained. Leathery thickening may affect whole placenta. Raised grey/white plaques may be present on skin of foetus.

Information by permission of Professor RW Else