What is miscarriage in cats and dogs?
Clinically, miscarriage is pregnancy loss
What is abortion?
Abortion is well-defined as the eviction of foetuses before full-term pregnancy, i.e., before the fertilised egg is capable of independent life. Abortion is unusual in the bitch. However, foetal reabsorption or mummification is more common.
What is foetal reabsorption?
It is also referred to as canine foetal resorption. It is a biochemical process whereby a puppy within the womb is absorbed. The tissues of a live foetal organism, the puppy, deteriorate and decompose completely through a process of disintegration of the enzymes in the foetus inside the womb allowing for complete destruction of the organism resulting in total reabsorption. Puppy absorption cannot happen after a certain amount of days (44 days roughly) because of the development of the skeletal bones, those of which cannot be reabsorbed. Therefore, canine reabsorption only occurs during the earlier stages of pregnancy when the foetus is made up of mostly soft tissues.
What is foetal mummification?
Foetal mummification refers to the death of foetuses after the calcification of the skeleton, around day 50 of the pregnancy in the dog. It often leads to the mummification of foetuses. The foetuses are retained within the uterus, and degradation happens to a certain extent, leaving the skin dry around the foetus, forming a membrane that may hinder full foetal decay and reabsorption for prolonged periods. Mummified foetuses are generally retained in non-infected uteri, and the general health of the dam is usually not affected. The skull and skeletal parts are also intact, and the foetus remains more or less distinguishable in the uterus by ultrasound and x-ray. Diseases of the uterus often lead to complete foetal dissolution and decomposition and may affect the dam’s health.
What are the differences between stillbirth and neonatal death?
A newborn puppy (neonate) born dead at full term is called a stillborn. Neonatal (newborn) death is judged to be loss of life within the first 3 weeks after the birth of the puppy.
What are the causes of abortion in cats and dogs?
The causes of abortion in cats and dogs are either infectious or non-infectious.
Infectious causes:
These can be broadly grouped into Viral, Bacterial, Fungal, and Protozoal diseases.
1. Viral causes
Common viral diseases causing abortions and neonatal deaths in dogs include:-
i). Herpesviral infection (most common cause)
ii). Bluetongue virus (BTV)
iii). Canine parvovirus-1 (canine minute virus),
iv). Canine distemper virus (CDV), and
v). Canine adenovirus-1 (CAV1).
Usually, foetal and neonatal deaths may possibly be secondary to maternal illness or due to direct infection.
Viral diseases causing abortions and neonatal deaths in cats include:-
i). Feline leukaemia virus,
ii). Feline parvovirus (feline panleukopenia virus),
iii). Feline immunodeficiency virus (FIV),
iv). Feline coronavirus, and
v). Feline calicivirus (FCaV).
2. Bacterial causes
Common bacterial diseases causing abortions and neonatal death in dogs starting with the most important are:-
i). Brucella canis
ii). Streptococcus spp infection.
iii). Escherichia coli,
iv). Campylobacter spp,
v). Leptospira spp, and
vi). Salmonella spp can occur sporadically.
Common bacterial diseases causing abortions and neonatal death in cats starting with the most important are:-
i). Streptococcus spp infection.
ii). Escherichia coli,
iii). Campylobacter spp,
iv). Leptospira spp, and
v). Salmonella spp can occur sporadically.
3. Fungal causes
Abortions due to fungal infections are rare in dogs and cats.
4. Protozoal causes
These are sporadic causes of abortions and neonatal deaths in cats and dogs.
The common protozoal disease that causes abortions and neonatal death in dogs is:-
i). Neospora caninum (Neosporosis)
The common protozoal disease that causes abortions and neonatal death in cats is:-
i). Toxoplasma gondii (Toxoplasmosis)
Prognosis: most bitches become immune to infectious cause (except canine brucellosis and probably herpesvirus infection) and subsequently reproduce normally.
Clinical signs of an aborting female dog or cat
i). Early milk production by mother. Milk usually only produced in the last 3-4 days of gestation and is not easy to express from the teats.
ii). Vomiting.
iii). Greenish vaginal discharge signifying foetal death.
iv). Symptoms of abdominal pain.
v). No signs of abortion or evidence of aborted puppies (because eaten by the mother).
vi). Reduced litter size or no puppies born (fetal resorption).
NB: Foetal death happening before the first half of pregnancy may go unnoticed for external signs of resorption or abortion during that stage may be minimal, not producing a significant amount of vulvar discharge or systemic illness.
Public health concerns:-
All abortions are potentially zoonotic.
Women of child-bearing age should be cautious to avoid handling the bitch, and any aborted material
Non-infectious causes of abortions in cats and dogs
1. Traumatic Causes
Traumatic causes of abortions in pets are subdivided into trauma during parturition, such as with dystocia (difficult delivery) and trauma occurring after birth (neonatal death). Neonatal trauma is characterised by locally extensive bleeding that may be accompanied by fractures of bones within the affected area.
Infanticide, a situation where the mother kills her infant, is often caused by skull-crushing and results in bleeding and fractures of the skull. Typically, more than one puppy or kitten in the litter may be affected. Dams that commit infanticide in one litter are at increased risk of committing infanticide in future litters.
2. Hereditary Defects and Genetic Disorders
Hereditary defects can be sporadic and without a direct cause. They can be a phenotypical (physical) reflection of a genetic disease or can be associated with toxin ingestion. Chromosomal defects typically result in early embryonic death and resorption.
3. Maternal factors
Anomalies in metabolism or nutrition, such as diabetes mellitus, hypothyroidism, eclampsia (low calcium levels), and pregnancy toxaemia (large litter sizes), can result in a foetal or neonatal loss in the bitch and queen. Insufficient pregnancy hormones (progesterone) also can cause abortions.
4. Other Causes of Neonatal Deaths
Subsequently, after birth, some kittens and puppies fail to thrive and are referred to by the phrase “fading syndrome.” The fading syndrome is a term used to describe a clinical presentation rather than a specific cause. This syndrome describes a wide variety of infectious, toxic, traumatic, metabolic, and genetic diseases. Maternal factors, such as mastitis, may also play a role.
Mechanism of miscarriages (Pathophysiology)
Bacteria produce toxins in the uterus (womb) that interfere with the placenta, causing it to release hormones (prostaglandin F2-alpha) that cause interferences in the ovaries and the uterus to contract. In cases where the uterus is inactive or fails to respond to foetal signals, this leads to primary uterine (womb) inertia, the most common cause of dystocia (difficult delivery) in dogs. Dystocia leads to hypoxia (reduced oxygen supply) that causes the anus of the foetus to relax, causing meconium (substances in the gut of the foetus) to escape into the amniotic fluid (fluid surrounding the foetus), and the foetus inhales it and dies.
How is pregnancy loss treated?
Broad-spectrum antibiotics are administered if there is a vulvar discharge, e.g. cephalosporins (20-30 mg/kg i.m, s.c. or orally q8-12h) or ampicillin (30 mg/kg i.v., i.m. or orally q6-8h). Tetracycline antibiotics are not used as they can cause foetal abnormalities (teratogenic). Hormones (progestogens) should not be used because they cause the retention of puppies that can lead to maceration and emphysematous (swollen) puppies. This can cause severe systemic illness in the mother. The foetus is then monitored for viability with an abdominal ultrasound.
How is pregnancy loss prevented?
A breeding program should be in place to ensure that no dog is used for breeding unless he or she has been tested for canine herpesvirus infection and brucellosis. Bitches that have aborted should be isolated, and the breeding area disinfected until investigations are complete.
Brucella spp. vaccines have not been developed, but a herpesvirus vaccine is commercially available (Eurican®, Merial Animal Health).
References
Braund, K., & Pinto, C. (2020). Abortion / stillbirth. Retrieved from Vetstream: https://www.vetstream.com
Concannon, P., Tsutsui, T., & Shille, V. ( 2001). Embryo development, hormonal requirements and maternal responses during canine pregnancy. . Journal of reproduction and fertility., 169-179.
Farstad, W. K. (2008). Pregnancy Loss and Abortion in Dogs. British Small Animal Veterinary Congress. Olso: British Small Animal Veterinary Association.
Gunzel-Apel, A.-R. (2003). Non-infectious causes of pregnancy loss/ abnormal pregnancy in the bitch. In: Pathology of canine and feline reproduction, physiology and pathology of the neonate. Reproduction in Companion, Exotic and Laboratory Animals, 17.1 - 17.11.
Johnston S D, R.-K. M. (2001). Canine and Feline Theriogenology. Philadelphia: WB Saunders Co.
Lamm CG, M. C. (2012, May). Current advances in gestation and parturition in cats and dogs. Vet Clin North Am Small Anim Pract., 42(3), 445-56. doi:10.1016/j.cvsm.2012.01.010.
Lamm, C. G., & Njaa, B. L. (2012). Clinical approach to abortion, stillbirth, and neonatal death in dogs and cats. Veterinary Clinics: Small Animal Practice, 42(3), 501-513.
Verstegen, J., Dhaliwal, G., & Vestegen-Onclin, K. (2008). Canine and feline pregnancy loss due to viral and non-infectious causes: a review. Theriogenology, 70 (3), 304-319.