Abstract
Problems in gestational development in dogs can be determined by infectious and non‐infectious causes. Among the non‐infectious causes, trauma during pregnancy, genetic characteristics of the animal, deficit nutrition, thyroid dysfunction, maternal problems and hormonal disorders are found. The majority of the cases are in relation to infectious diseases, one should consider viral, bacterial, fungal and protozoal, which can interfere directly or indirectly in the foetal development. The progression of foetal development may be affected by the direct action of the microorganisms to overcome the placenta, but they are also able to affect pregnancy and release placental toxins by inflammatory processes and, may still cause maternal pathologies, which entail problems such as hyperthermia, hypoxia and endotoxemia, which can result in abortion. Several diseases can trigger pregnancy loss in dogs. This action can be direct by microorganisms, as well as indirectly triggering other problems that lead to abortion. This chapter discusses the infectious aetiologies of reproductive failures (abortion, stillbirth and neonatal death) in bitches.
Keywords
- Puppies
- Bitches
- reproductive failure
- infectious causes
- diagnostic
1. Introduction
Problems in gestational development in dogs can be caused mainly by infectious diseases. The progression of foetal development may be affected by the direct action of microorganisms to overcome the placenta, but they are also able to affect pregnancy and release placental toxins by inflammatory processes and may still cause maternal pathologies, which entail problems such as hyperthermia, hypoxia and endotoxemia, which can result in reproductive failures (abortion, stillbirth and neonatal death) [1].
2. Bacterial diseases
2.1. Brucellosis
The bacterium
2.2. Others bacterial agents and Rickettsias
The
3. Protozoal diseases
Some protozoan species are capable of infecting dogs and can also infect humans, triggering zoonoses. The existence of protozoal coinfection in dogs are already established, one of the combination of
The
3.1. Toxoplasmosis
The evidence of facts relating to such a manifestation of the parasite in dogs is scarce. What is known is that in its life cycle, the
Animals infected with
The possible interference of Toxoplasmosis in the reproduction of dogs as a whole has been studied in 1970 and found out that toxoplasma infection in dogs at various gestational stages can cause mortality of the puppies from the 4th to 75th postnatal days [13]. Still, abortion and foetal death has been observed, in the middle third and final pregnancy in dogs experimentally infected with
Diagnosis of toxoplasmosis is mainly based on clinical suspicion since the symptoms can be similar to other infectious diseases. Therefore, attention should be paid to the epidemiological information and data collected during the interview, making a request for additional tests, a prerequisite. In dogs, the presence of apathy, rhinorrhea, conjunctivitis, pneumonia, fever, convulsions, paralysis, diarrhoea and lymphadenopathy may be clinical signs of
In cases of acute systemic infection in dogs changes can be observed in haematological parameters, such as nonregenerative anaemia, neutrophilic leucocytosis, lymphocytosis, monocytosis and eosinophilia. The biochemical changes are consistent with increased serum activities of alanine aminotransferase (ALT) and alkaline phosphatase may occur when there is liver necrosis. If necrosis is acute, bilirubin levels are likely to be increased. In the event of muscle necrosis, serum creatine kinase activity is also increased [7]. The establishment of the diagnosis can be made through serological tests, but there is no absolute serologic test that can definitely confirm the diagnosis of toxoplasmosis. Furthermore, only the detection of antibody against the parasite is not sufficient for the establishment of serological diagnosis since previously infected dogs may also exhibit antibodies response. Some tests that may be ordered in addition to the IFT and MAD, such as the reaction of Sabin‐Feldman (SF), the enzyme linked immunosorbent assay (ELISA), complement fixation test (CF) and the reaction of indirect haemagglutination (HI) [8].
The IFA identifies antibodies through specific fluorescent conjugates of IgG and IgM. The presence of IgG is related to a previous exposure, suggesting active and recent infection. The MAD evaluates IgM antibodies indirectly by subtracting antibody titres present in treated and untreated sera [19]. The SF reaction has a high sensitivity and specificity and allows the antibody titration within a few days post‐infection. The enzyme linked immunosorbent assay allows detection of IgM response. In the CF test, different parasite antigens are used and that can be identified as testing positive in case of an early infection. In short, the interpretation of the results: a high titre of IgM with low or zero IgG indicates a disease evolving, otherwise, the high quantitation of IgG and low or zero IgM indicate a chronic state of the disease. Whatever the outcome, a new serology test should be done after 15–21 days due to the possibility of severe immunosuppression until the second post‐infection week, which may lead to false‐negative results [8]. Identifying the
Various infectious and non‐infectious diseases should be evaluated in the differential diagnosis of toxoplasmosis. In dogs, the most relevant are distemper, neosporosis, isosporiasis and strongyloidiasis [8]. In aborted foetuses, macroscopically it is possible to observe necrotic foci white‐greyish punctate located in the lungs and liver, as well as pulmonary congestion and heart pallor. The central nervous system (CNS) is marked with congestion of the brain and cerebellum [7].
Treatment of toxoplasmosis is based on suppression of the replication agent when the disease presents itself in the acute form, and emphasizes the importance of early diagnosis and consistent implementation of measures leading to the reduction in disease transmission [20]. Clindamycin is the drug of choice for the treatment of dogs and cats. The drug administration once started, the clinical signs tend to initiate regression after 24 – 48 hours. In addition to clindamycin, the combined use of pyrimethamine and fast‐acting sulphonamides (e.g., sulfadiazine, sulfamethazine and sulfamerazin) is valid in the treatment of systemic toxoplasmosis infection [7].
Prevention should be taken to avoid ingestion and contact with oocysts and cysts. So for pets that eat meat, the meat should be well cooked. As a complement to prevention, measures should be taken to avoid these same animals hunt and/or eating mechanical hosts such as cockroaches, flies, worms and rodents, potential or intermediate hosts. The prevention becomes even more important because there is no vaccine available for humans or animals [8]. General care in food hygiene, whether in urban or rural areas, considering proper cooking of meat and milk boiling, are the main preventive measures of toxoplasma infection to humans. Personal hygiene and comprehensive hand washing performed after handling raw meat, for example, assists in preventing the disease. Generally, prevention of human toxoplasmosis is based on the maximum avoidance of exposure to susceptible hosts. This disease is not notifiable, except for outbreaks [7].
3.2. Neosporosis
Neospora is a protozoan belonging to the phylum Apicomplexa, Sporozoa class, Eucoccidiida order and Sarcocystidae family [21].
Horizontal transmission (postnatal) is due to the ingestion of water or food contaminated with oocysts eliminated by dogs, especially in cases of abortion outbreaks. It is identified as the association between seroprevalence and abortions in bovines, when the presence of dogs could increase the incidence of the disease in both species. Dogs present in farms were identified with greater prevalence of infection than in urban area [36]. This is due to the dogs ingest infected bovine foods such as foetuses, foetal membranes and fluids [37]. In dogs, neosporidiose can develop neuromuscular, cardiac, pulmonary and skin lesions changes, there still descriptions of dermatitis, cardiomyosite and pneumonia in this species [38, 39]. Vertical transmission via lactogenic have been reported in calves experimentally and the presence of DNA of
Contamination can occur vertically when a bitch with subclinical infection transmits
The PCR is essential to detect the DNA of the parasite in the faeces of the definitive host and thus used to confirm the diagnosis. This technique is also used to perform DNA detection in the intermediate host [46, 47]. Serological tests such as indirect immunofluorescence assay, agglutination test Neospora (NAT) and multiple tests of ELISA were made for diagnosis in dogs [48]. IFA was the initial test to identify antibodies against
Macroscopic lesions caused by
4. Viral diseases
4.1. Canine herpesvirus
The canine herpesvirus 1 (CHV‐1) has a worldwide distribution and is associated with respiratory and reproductive diseases in dogs [54]. The CHV‐1 was isolated in several countries, with a disease considered enzootic for dogs [55]. The first study to report this agent associated with fatal haemorrhagic disease in puppies was Carmichael et al. in 1965 [56]. The
Among the infectious diseases of viral origin, the CHV‐1 stands out as one of the main viral cause of abortion and neonatal mortality in dogs [60]. The infection caused by this virus during pregnancy can lead to abortion, stillbirth, embryonic resorption, premature birth and neonatal death [61, 62]. It can result in infertility, birth of mummified foetuses, weak puppies, or premature sick [55]. Its horizontal transmission can occur due to direct or indirect contact between dogs. This contact can happen through nasal secretions, semen and contaminated aerosols, regardless of sex or age distinction, being observed an increased susceptibility in puppies less than 2 months [63]. Animals without updated immunization record, with vaccination failures and maternal immunization also become more prone to infection [64]. Vertical transmission occurs from mother to foetus through the placenta [55]. In some cases the infection can reach the uterus resulting in foetal death and still birth of the offspring [65]. After infection of the cell by the virus in the cell nucleus will be synthesis of viral DNA and nucleocapsids. As the viral envelope from the nuclear membrane. The virus then travels through the endoplasmic reticulum and Golgi, and subsequently released to infect new cells [58].
Infected adult dogs often do not show apparent symptoms. In them, the infection is often subclinical. However, in newborns and puppies with 1–2 weeks of life may develop systemic disease that may result in a generalized necrotizing haemorrhagic disease [55, 56]. Still, this pathogen has an important characteristic of latent infection remaining in a state of latency in lymph nodes and lymphoid tissues of the oronasal mucosa and genital [58, 66]. So that makes the diagnosis difficult due to the absence of clinical signs. In this condition, the presence of factors such as pregnancy, stress, immunity reduction, diseases and use of corticosteroids can reactivate the virus [58], with the possible occurrence of necrosis in the placenta in pregnant infected bitches [65]. In females, papulovesicular in genitalia and oral lesions can be visualized, and in males, may be similar lesions on the penis and release the virus by semen [58]. The histopathologic examination of the liver, lung and kidney in adult dogs reveals haemorrhages with necrotic foci and intra‐nuclear inclusion bodies. Puppies contaminated by CHV‐1 usually die resulting from systemic disease. The consequences of pathogen infection during pregnancy in bitches will depend on the stage of gestation when infection occurred. Histopathological and post‐mortem exams may be observed mummified and calcified foetuses, foetuses with progressive multifocal haemorrhagic necrosis in various organs, and haemorrhagic foci in uteri and placentas. An increased virus concentration has also been observed in the adrenal glands, kidneys, lungs, spleen and liver. In the post‐mortem examination the presence of serous fluid and haemorrhage in the pleural and peritoneal cavities is observed. And especially in canine puppies infected by the oronasal route may have meningoencefatite after birth [58].
Diagnosis can be accomplished through fluids and vaginal swabs collected and nasal secretions, or using tissues from foetal organs or adult dogs after necropsy. The antigen or genetic material in aborted foetuses or newborns can be extracted from humours, liver, adrenal glands, lungs, spleen, kidneys and lymph nodes. With the collection of the appropriate material, histopathological tests, biochemical, immunofluorescence microscopy and molecular tests can be performed. The CHV‐1 presence can be confirmed in samples by polymerase chain reaction [63] and by the sequencing, comparing similarity between the surrounding sequences. PCR allows for viral detection even in animals that have the latent infection [58]. Obtaining the history and medical records of these animals is also essential for a complete and accurate diagnosis [67]. The treatment of this disease in puppies is difficult due to the rapid development of infection and mortality that occur before the diagnosis is established [58]. However, despite this agent being seen as the main cause of abortion and foetal mortality in dogs, other pathogens may be associated directly or indirectly with these consequences, such as loss of pregnancy by systemic infectious anaemia [1]. Vaccination and appropriate sanitary measures are essential to prevent viral spread among animals in kennels [63].
4.2. Canine minute virus
Another viral agent that can cause severe disease in newborns, transplacental infections and embryonic resorption in dogs is
The clinical signs found in CnMV infection may vary, be unapparent, or apparent as respiratory problems, enteric disease and reproductive disorders [71]. Infected puppies less than 1 month of age may have mild symptoms or accelerated death, depression, lack of appetite, acute myocarditis, respiratory failure and enteritis. The viral action mechanism contributes to reducing phagocytosis by monocytes promoting immunosuppression [68, 72]. The transplacental infections can cause disease in subclinical phase, deformations of foetuses and the loss of pregnancy. The consequences in pregnant bitches may vary according to the time of infection. In the first half of the pregnancy, stillbirth and embryo resorption process can occur after infection. In the second half, observed a larger number of stillborn and weak puppies [71].
As for post‐mortem examinations on puppies, pneumonia, enteritis, myocarditis, oedema and atrophy of the thymus have been observed. In relation to the histopathologic findings, viral presence in the epithelial cells of the intestinal crypts and cardiomyocytes are observed. Other changes found are hyperplasia of the interstitial crypts, myocardial necrosis, pneumonia, and depletion of lymphocytes in the thymus and other lymphoid tissues [71]. The samples for diagnosis may vary mostly from foetal or neonatal tissues of the myocardium, intestine, lungs, kidneys and faeces. The diagnosis of the CnMV can be accomplished by direct methods such as viral isolation, immunohistochemistry, electron microscopy, direct ELISA, conventional PCR and RT‐PCR, of the tissue, and/or faeces and/or enteric contents. For detection of intranuclear inclusion bodies, haematoxylin‐eosin staining or immunofluorescence using specific antibodies [73] can be used. As for indirect methods of serological diagnosis may used the indirect ELISA and haemagglutination inhibition, allowing the study of the prevalence of disease [74].
The treatment of parvovirus is based on the recovery of electrolyte balance and in the prevention of secondary infections using antibiotics. Attenuated vaccines of CnMV in dogs provide superior immunity than inactivated, and are safer. In newborn puppies, it is suggested the warming of them and to maintain nutrition and adequate hydration [74].
4.3. Other viral diseases
Other viral infections known to cause abortions, stillbirths and neonatal death in bitches are Bluetongue (BTV), canine distemper and canine adenovirus‐1 [75]. The Bluetongue is a disease transmitted by arthropods especially in ruminants. Infection of dogs is currently thought to be by oral ingestion of infected meat or meat products rather than through vector feeding [76]. There is evidence of direct transmission of the agent to the dog. Abortion and stillbirth are consequences of infection of this agent in pregnant bitches [77]. Direct transmission and differences in canine susceptibility to certain serotypes of the virus are not well elucidated in dogs [78]. The canine distemper virus (CDV) may also affect gestation by the weakness of maternal health inducing abortion, and in rare cases can cross the placenta and lead to abortion or foetal infection [79, 80]. The abortion can originate from a systemic infection in dogs or transplacental infection [81]. The infection by this virus can still result in stillbirth and congenital infections in dogs. Transplacentally infected puppies can develop neurologic signs within 6 weeks after birth [79, 82]. The canine adenovirus‐1 (CAV‐1) may be associated with fatal pneumonia in pups less than 1 month of age [83]. However, this virus can result in miscarriage, with or without foetal infection. Abortion can be a result of stress caused by the disease [79, 80].
5. Final considerations
Infectious causes are still the most responsible for reproductive failure in dogs through the direct action of the pathogen in the foetus and in placenta; however, we must always try to reduce the chances of reproductive failures that occur due to systemic action of the infectious agent in the mother through the early diagnostic and treatment.
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