4. Viral diseases

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].

Neospora is a protozoan belonging to the phylum Apicomplexa, Sporozoa class, Eucoccidiida order and Sarcocystidae family [21]. Neospora caninum is a parasite coccidia, intracellular exclusively, forming cysts that causes neosporidiose, a disease that has been disseminated in the continents generating a high rate of infected cattle and dogs [22]. In the genus Neospora were identified only two species N. caninum [23] isolated from dog brain and N. hughesi [24, 25] isolated from the brain and spinal cord of horses [24]. It has not been described any cases of the disease in humans [26]. Dogs (Canis lupus familiaris) [27], coyotes (Canis latrans) [28], dingo (Canis lupus dingo) [29] and gray wolves (Canis lupus) [30] have been identified as definitive hosts of the parasite and are significant in the transmission of the parasite to other animals. The prevalence of antibodies against N. caninum in dogs is the result of research in various parts of world, which has reached from 4 to 54.2% [31, 32]; this percentage can be varying because of habitat, age, living of dogs with cattle, diet and serological technique employed etc., among others [33]. The life cycle of N. caninum has three forms: tachyzoites, bradyzoites in the cysts and sporozoites in the oocysts. However, the tachyzoites and bradyzoites are intracellular stages identified in intermediate hosts [34]. The tachyzoites are responsible for the acute phase and has the ovoid or circular shape. Bradyzoites are in latent stages, through tissue cysts that

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 N. caninum was also observed in the colostrum of cows infected, reporting the

Contamination can occur vertically when a bitch with subclinical infection transmits N. caninum to its foetuses and litters can be born infected [41]. The congenitally infected animals are the most severe cases; however, the infection can occur in animals of all ages. Young animals manifest hind limb paralysis that occurs at an accelerated rate, and incoordination can cause paresis of hind limbs in adult dogs [42, 43]. For a reliable diagnosis: detailed history and description, good physical examination and laboratory tests are necessary [42]. Haematological and biochemical tests are not enough to confirm the diagnosis of this

3.2. Neosporosis

are resistant to acid solution pepsin [35].

62 Canine Medicine - Recent Topics and Advanced Research

possibility of transmission of N. caninum by colostrum [40].

#### 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 Canid alphaherpesvirus 1 species refers to family Herpesviridae, subfamily Alphaherpesvirinae and genus Varicellovirus [57]. This virus consists of double‐stranded DNA, has icosahedral infecting only dogs or cells canine origin. This specificity is due to the presence of specific receptors on the cell surface, such as the glycoprotein D (haemagglutinin) [54, 58]. As for CHV‐1 characteristics of the environment, there is a higher incidence and spread of the virus in kennels than in the home environment. The presence of this agent in serum from canis can get up to 100%. This fact is mainly due to agglomeration and poor hygiene conditions in places [58]. Moreover, the disease manifests itself in seasonal way, accentuating in cold weather because the virus is unstable and sensitive to higher temperatures [58, 59].

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

icosahedral infecting only dogs or cells canine origin. This specificity is due to the presence of specific receptors on the cell surface, such as the glycoprotein D (haemagglutinin) [54, 58]. As for CHV‐1 characteristics of the environment, there is a higher incidence and spread of the virus in kennels than in the home environment. The presence of this agent in serum from canis can get up to 100%. This fact is mainly due to agglomeration and poor hygiene conditions in places [58]. Moreover, the disease manifests itself in seasonal way, accentuating in cold weather because the virus is unstable and sensitive to higher temper-

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

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

atures [58, 59].

64 Canine Medicine - Recent Topics and Advanced Research

infect new cells [58].

Another viral agent that can cause severe disease in newborns, transplacental infections and embryonic resorption in dogs is Canine minute virus (CnMV) or CPV‐1 (Canine Parvovirus‐1) [68]. This agent sets off a disease currently considered endemic [69]. The consequences of infection with this virus in pregnant females may vary according to the time of infection during pregnancy and may cause embryonic resorption, stillbirth, neonatal mortality and abortion [65, 70], or initiate respiratory, cardiac and enteritis problems in puppies [65]. The CnMV is a parvovirus that belongs to Parvoviridae family, subfamily Parvovirinae and genus Bocavirus [57]. It is a very small virus approximately 22 nm in diameter, single‐stranded DNA and has no viral envelope. This virus has tropism for lymphoid and embryonic tissues, bone marrow, myocardium and intestinal epithelium [69].

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].
