Mastitis is defined as inflammation of the parenchymal tissue of the mammary gland, regardless of its cause. Mastitis cases with unidentified etiology have drawn attention to the possible role of viruses. Viruses whose activity has been detected directly or indirectly in cattle with clinical mastitis have also been reported to play an important role in subclinical mastitis, causing significant economic losses in milk production. In sheep and goats, maedi-visna virus and caprine arthritis-encephalitis virus have been reported as important viral mastitis agents. In this review, the results of studies conducted on mastitis in cattle, sheep, and goats are evaluated. The reviewed studies reveal that viral agents can replicate in mammary tissue and cause lesions, lead to mastitis associated with secondary infections due to virus-induced immunosuppression, and result in physical and chemical changes in milk. Consequently, there is a need to develop rapid diagnostic methods and antiviral agents to identify viral causes of mastitis, as well as to conduct studies to determine viral agents involved in mastitis in our country.

• Cattle viruses

• Sheep and goat viruses

• Viral mastitis

AKMAN A, GÜMÜ?OVA S (2026) Viral Mastitis in Cattle, Sheep, and Goats. J Vet Med Res 13(1): 1293

Although the role of viruses in mastitis cases of economic importance in cattle, sheep, and goat breeding is considered less significant than that of bacterial agents, their direct and indirect effects result in considerable economic losses. Mastitis is defined as inflammation of the parenchymal tissue of the mammary gland, regardless of cause. Infection is characterized by a series of pathological disorders in mammary tissue, accompanied by physical and chemical changes in milk. In many clinical cases, swelling, fever, pain, and edema of the udder are observed. In addition, discoloration of milk, presence of clots, and increased leukocyte counts are detected. Mastitis is characterized according to its cause (physical or infectious) [1].

Due to the focus of mastitis research on bacterial pathogens, the impact of viral infections on mastitis was recognized relatively late. Furthermore, difficulties in diagnosing subclinical mastitis, improper collection and storage of milk samples for virological analysis, and the labor-intensive and costly nature of laboratory diagnosis of viral mastitis have all contributed to the underestimation of viral involvement in mastitis.

Mastitis is a common disease in dairy cattle and represents a major economic burden for milk producers worldwide [2]. The disease generally causes inflammation in one or more udder lobes and may affect the entire herd or only a few animals within it [3].

Miltenburg et al. [4], detected no pathogens in 28% of animals with clinical mastitis, while Wedderkopp [5], reported no pathogen detection in 35% of such cases.

Bovine Herpesvirus 1 (BHV-1)

In 2009, a study conducted on bulk tank milk samples in Irish dairy herds aimed to determine the national prevalence of exposure to BHV-1 and BVDV. Milk samples collected periodically from 305 herds were tested by ELISA. Approximately 60% of the examined cattle were vaccinated against BVDV using inactivated vaccines, and 12.5% were vaccinated against BHV-1 using DIVA vaccines. Annual positive bulk tank milk measurements were reported as 88% for BVDV (80% in unvaccinated herds) and 80% for BHV-1 (78% in unvaccinated herds) [6].

Experimental BHV-1 infection of the mammary gland has been shown to cause necrosis in the alveolar epithelial layer, accumulation of polymorphonuclear and mononuclear cells, and intranuclear inclusion bodies in epithelial cells [7]. Overall, studies indicate that BHV-1 can cause mastitis following vaccination or experimental infection and can be isolated from teat lesions.

Bovine Herpesvirus 4 (BHV-4)

BHV-4, a member of the subfamily Gammaherpesvirinae within the Herpesviridae family, has been isolated from cattle with chronic ulcerative mammary dermatitis [8] and detected in 4% of mastitis cases alongside bacterial pathogens such as Staphylococcus aureus and Streptococcus uberis [9]. Studies have also demonstrated that BHV-4 infection increases the incidence of mastitis caused by S. uberis [10] and S. aureus [11]. Supporting these findings, Ali et al. [12] detected BHV-4 antibodies in 98% of dairy cattle infected with S. aureus or S. uberis.

Foot-and-Mouth Disease (FMD) Virus

FMD virus, a member of the genus Aphthovirus within the family Picornaviridae, can replicate in epithelial cells of the mammary gland. The virus has been isolated from milk of infected cattle [13]. Lesions in the teat canal caused by FMD virus may predispose the udder to secondary infections with Arcanobacterium pyogenes, contributing to mastitis [14].

Sharma [15], investigated six lactating crossbred cattle in a private dairy farm in India. Three animals had a history of abnormal clotted milk and teat swelling, and a foot-and- mouth disease outbreak had occurred on the farm 20 days earlier. Milk yield decreased from 14–16 liters per day to 2–3 liters. FMD-related teat erosions were observed, facilitating bacterial mastitis.

Bovine Leukemia Virus (BLV)

BLV, a member of the genus Deltaretrovirus within the Retroviridae family, has been detected by electron microscopy in mammary tissues of BLV-seropositive cattle with subclinical mastitis [13]. Szewczuk et al. [16], reported that BLV-infected cattle produced 4.3% less milk than healthy cattle.

Bovine Herpesvirus 2 (BHV-2)

BHV-2 causes bovine mammillitis, characterized by painful ulcerations on the udder and teats, as well as vesicular lesions on the skin [17]. In severe infections, destruction and dysfunction of the teat canal may occur [18]. Chronic mastitis has been observed in cattle with teat ulcers, and impairment of the udder’s mechanical defense mechanisms is believed to facilitate BHV-2–associated mastitis.

In Pennsylvania, composite milk samples collected every three days from 139 lactating cows were analyzed using PCR and somatic cell count (SCC) methods, revealing positivity rates of 10%, 28%, and 0.7% for BHV-1, BHV-2, and BHV-4, respectively [19].

Vaccinia Virus (VACV) and Cowpox Virus (CPXV)

VACV and CPXV, members of the genus Orthopoxvirus within the family Poxviridae, produce clinical symptoms similar to those caused by BHV-2 [20]. During a VACV outbreak in Brazil, 10 of 13 lactating cows (76.9%) exhibited exanthematous and hemorrhagic lesions progressing to vesicles, pustules, and ulcers on the teats. VACV was detected by PCR in milk samples from five cows with subclinical mastitis (>200,000 SCC) and in crusted teat lesions [21].

Pseudocowpox Virus and Bovine Papular Stomatitis Virus (BPSV)

Pseudocowpox virus causes significant losses by complicating milking and increasing mastitis incidence [1]. Wellenberg et al. [9], reported that the virus disrupts the udder’s mechanical defense mechanisms and was detected in 5 of 14 teat lesions examined.

BPSV is a parapoxvirus associated with papular and erosive lesions of the oral mucosa, lips, and nasal planum of cattle and has also been reported to cause teat lesions in dairy cows [22]. During a BPSV outbreak in Brazil in 2010, virological testing of crusts from 20 manually milked cows confirmed infection [23].

Bovine Papillomaviruses

Bovine papillomaviruses, belonging to the genus Papillomavirus within the family Papillomaviridae, cause fibropapillomas on the teats [24]. These lesions may disrupt natural defense mechanisms of the teat canal, predisposing animals to mastitis [25] and bacterial infections [26].

Bovine Viral Diarrhea Virus (BVDV)

BVDV, a member of the genus Pestivirus within the family Flaviviridae, is an immunosuppressive virus [27]. Studies in exposed herds have shown a 7% increase in the incidence of clinical mastitis, likely due to impaired mammary defense mechanisms during acute BVD infection [28]. Yavru et al. [29], detected BVDV antibodies in 82.6% of blood serum samples and 79.2% of milk serum samples using ELISA.

Bovine Immunodeficiency Virus (BIV)

BIV, a lentivirus within the Retroviridae family, causes immunosuppression and central nervous system lesions and has been associated with chronic mastitis in approximately 40% of infected animals [30]. In another study involving 15 Holstein cattle, mastitis contributed to secondary disease processes at a rate of 56.25% [31].

Mastitis is a major cause of culling in sheep and goats and poses a significant problem in husbandry, particularly in dairy small ruminant farms. Economically threatening infections are mainly caused by small ruminant lentiviruses (SRLV), including maedi-visna virus in sheep and caprine arthritis-encephalitis virus in goats [32]. Chronically infected animals exhibit signs such as poor body condition and hardened udders. The infection is primarily transmitted from dam to offspring via colostrum and milk [33].

Maedi-Visna Virus (MVV)

Experimental studies by van der Molen and Houwers [34], demonstrated an association between MVV infection and lymphocytic mastitis in sheep. Asadpour et al. [35], analyzed milk samples from Iranian flocks using PCR and detected MVV in 7 of 40 CMT-positive samples and in 1 CMT-negative sample, indicating that 16.5% of sheep with subclinical mastitis were infected with MVV.

Caprine Arthritis-Encephalitis Virus (CAEV)

CAEV-seropositive animals have been reported to exhibit higher somatic cell counts compared with seronegative animals [36]. Nord and Adnoy [37], also found higher SCC values in two-year-old seropositive dairy goats.

The reviewed studies demonstrate that viral agents can replicate in mammary tissue, cause lesions, induce immunosuppression, and thereby contribute to mastitis development through secondary infections. Viral agents capable of causing clinical or subclinical mastitis also induce physical and chemical changes in milk. Therefore, investigation of viral agents, in addition to bacterial pathogens, is essential in mastitis cases.

In conclusion, the development of rapid diagnostic methods and antiviral agents is crucial for identifying viral causes of mastitis. Further studies are needed to determine whether viral agents act as primary pathogens in mastitic milk samples or whether latent viral infections are reactivated by primary bacterial infections, as well as to identify viral agents involved in mastitis in our country.

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