Silent Infections That Can Destroy a Healthy Litter: The Hidden Infectious Causes of Canine Pregnancy Loss

A healthy pregnant bitch can suddenly abort, deliver weak puppies, or lose an entire litter within days — sometimes without showing severe illness herself. 

Behind these cases are often silent infectious agents that spread unnoticed through breeding kennels, contaminate environments, and continue affecting future pregnancies long after the first reproductive failure. Some of these pathogens are even capable of infecting humans, making early recognition and prevention critically important¹. 

In canine reproduction, infectious diseases remain one of the most underestimated causes of infertility, embryonic loss, abortion, stillbirths, and neonatal mortality¹. 

Brucella canis: The Most Feared Reproductive Infection 

Among all infectious reproductive diseases, Brucella canis remains one of the most devastating. The bacterium spreads through reproductive fluids, aborted tissues, urine, semen, and contaminated environments^1,2. 

Abortions commonly occur between days 45–55 of gestation and may be followed by prolonged gray-green vaginal discharge. Infected litters may include weak puppies, stillbirths, or neonates that die shortly after birth¹. 

Male dogs can also develop orchitis, epididymitis, prostatitis, poor semen quality, and infertility. 

One of the biggest challenges with B. canis is diagnosis. False-negative results are common, particularly during early infection, making repeated testing necessary^1,3,4. Once introduced into a kennel, the infection can become extremely difficult to eliminate. 

The Growing Concern Around Raw Feeding 

The increasing popularity of BARF and raw meat diets has introduced additional infectious risks in breeding dogs. 

Improperly handled raw food may carry pathogens such as Campylobacter jejuni, Salmonella spp., Listeria monocytogenes, and Toxoplasma gondii¹. These organisms may contribute to abortion, weak puppies, neonatal death, or systemic illness. 

Some infected dogs may show only mild gastrointestinal signs — or no signs at all — before reproductive problems appear. 

Bacterial Infections That Often Go Unnoticed 

Several bacterial pathogens have been linked to reproductive failure in dogs. 

Campylobacter jejuni has been associated with abortions around the 45th day of gestation and may spread through contaminated food sources. Salmonella spp. can cause late-term abortion, septicemia, and reproductive complications. 

Although Escherichia coli normally exists within the canine reproductive tract, certain strains may trigger abortion between days 41–55 of gestation^1,5. 

Beta-hemolytic streptococci have also been connected to abortion, infertility, and neonatal septicemia, highlighting the importance of bacterial culture in reproductive investigations¹. 

Viral Infections and Neonatal Death 

Few diseases are as heartbreaking as canine herpesvirus-1 (CaHV-1). The virus is strongly associated with fading puppy syndrome and neonatal mortality^1,6. 

Puppies younger than two weeks are especially vulnerable because the virus replicates more efficiently at lower body temperatures. Clinical signs may include weakness, respiratory distress, abdominal pain, and sudden death. 

Maintaining neonatal warmth above 38 °C can significantly reduce viral replication and improve survival rates. Vaccination during pregnancy may also help reduce neonatal losses¹. 

Other viral infections linked to reproductive loss include canine parvovirus type 1, canine distemper virus, and canine adenovirus². 

Protozoal Diseases and Vertical Transmission 

Protozoal infections can silently spread from mother to fetus during pregnancy. 

Toxoplasma gondii may cause fetal death, abortion, and systemic disease in newborn puppies¹. Exposure commonly occurs through contaminated food, water, or contact with infected cat feces. 

Neospora caninum is particularly concerning because of its ability to cross the placenta and infect developing fetuses². Puppies born with neosporosis may later develop hindlimb paralysis, muscle wasting, and severe neurological disease. 

In endemic regions, Leishmania infantum has also been linked to placentitis, vertical transmission, and reproductive failure¹. 

Prevention Starts Before Breeding 

Preventing infectious reproductive disease requires more than simply treating abortion cases after they occur. 

Routine infectious disease screening, vaccination, proper sanitation, quarantine protocols, and careful nutritional management all play major roles in protecting breeding animals and future litters. 

Breeding dogs should be screened before mating whenever possible, particularly in kennels with a history of infertility, abortion, or neonatal mortality. 

The Bigger Picture 

Pregnancy loss caused by infectious disease rarely affects just one litter. Without proper identification and control, the same pathogens may continue circulating through breeding populations, resulting in repeated reproductive failure and long-term kennel losses. 

Recognizing the hidden infectious causes behind canine pregnancy loss is therefore essential for improving reproductive success, neonatal survival, and overall kennel health. 

References  

1. Mantziaras G, Zakosek Pipan M. “My Bitch Is Empty!” An Overview of the Reasons for Pregnancy Loss in Dogs. Veterinary Sciences. 2025 Feb 5;12(2):127. https://doi.org/10.3390/vetsci12020127  

2. Santos RL, Souza TD, Mol JP, Eckstein C, Paíxão TA. Canine brucellosis: an update. Frontiers in veterinary science. 2021 Mar 2;8:594291. https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2021.594291/pdf  

3. de Souza TD, de Carvalho TF, Mol JP, Lopes JV, Silva MF, da Paixão TA, Santos RL. Tissue distribution and cell tropism of Brucella canis in naturally infected canine foetuses and neonates. Scientific reports. 2018 May 8;8(1):7203. https://www.nature.com/articles/s41598-018-25651-x.pdf  

4. Olsen SC, Palmer MV. Advancement of knowledge of Brucella over the past 50 years. Veterinary pathology. 2014 Nov;51(6):1076-89. https://journals.sagepub.com/doi/pdf/10.1177/0300985814540545 

5. Fontbonne A. Causes of pregnancy arrest in the canine species. Reproduction in Domestic Animals. 2023 Sep;58:72-83. https://onlinelibrary.wiley.com/doi/pdf/10.1111/rda.14407  

6. Mir F, Fontaine E, Albaric O, Greer M, Vannier F, Schlafer DH, Fontbonne A. Findings in uterine biopsies obtained by laparotomy from bitches with unexplained infertility or pregnancy loss: an observational study. Theriogenology. 2013 Jan 15;79(2):312-22. https://www.academia.edu/download/99726774/j.theriogenology.2012.09.00520230312-1-ymweri.pdf