Respiratory system disease complex of cattle (BRDC) is one of the commonly observed multifactorial health problems around the world. In its ethiology, it contains many pathogen factors such as viral ones like BPIV3, BHV-1, BCoV, BRSV, BAV, BVDV and bacterial ones like Pasteurella multicidae, Mannheimia haemolytica, Histophilus somni (Griffin et al. 2010; Headley et al. 2018). One of the most important viral factors providing a basis for this disease complex, BPIV3, usually occurs during autumn and winter months and mostly proceeds subclinically. Depending on the decrease in animal welfare based on infection, weight loss, decrease in quality of carcase, prophylaxis, increase in expenses of veterinarian services, decrease in fertility and fatal bronco pneumonias caused by joining of other pathogens to the infection cause breeders to have extensional economic losses (Ellis 2010). Serological and epidemiological researches performed on livestock and dairy animals show that BPIV3 is endemic all over the world (Tiwari et al. 2016). Besides, a seropositivity at the rate of 18-94.6% was detected in serological researches in Turkey (Alkan et al. 2000; Yıldırım et al. 2009; Kale et al. 2013; Gür 2018).
In this study, molecular diagnosis of BPIV3 was aimed to be revealed by RT-PCR technique in nasal swab, conjunctival swab and leukocyte samples of 190 non-vaccinated animals of different race, gender and ages showing respiratory system infection clinical findings and antigenic diagnosis of BPIV3 in nasal and conjunctival swab samples of the same animals by DIF method. In order to see the effects of the virus on tissue damage, a histopathological examination was carried out in lung tissue samples following the necropsy of an animal diagnosed with BPIV3 by antigenic and molecular methods.
Virus isolation could not be performed in our cell culture planting process. Similar to our study, in their study, Noori et al. (2014) performed an agent isolation from cell culture passages in only one out of 25 samples detected as positive in DIF and PCR analysis. The reason of this was thought that the agent had a fragile structure and could be isolated from a single sample since it could hardly adapt to cell lines. These results show the hardships of cell culture studies in diagnosing BPIV3 infection.
In many countries of the world, there are studies on molecular detection of BPIV3 (Zhu et al. 2011; O’Neill et al. 2015; Moore et al. 2015; Veljovic et al. 2016; Kishimoto et al. 2017; Headley et al. 2018; Kamdi et al. 2020). In these studies, the agent prevalence varied between 0% and 21.6%. Similar to these studies, in those in Turkey, Hacıoğlu (2011) obtained a positivity at the rate of 1.41% (1/71) in nasal swab samples by RT-PCR technique, Timurkan et al. (2019) 1.94% (3/155) in nasal swab and lung tissue samples and Toker and Yesilbağ (2021) 0.51% (1/193) in nasal swab and lung tissue samples. In addition, in their study on teat tissue samples by qRT-PCR technique, Çomaklı et al. (2019) detected BPIV3 viral genome at a rate of 21.67% (26/120).
This difference in prevalence values was believed to differ depending on the specifity (different primers) and sensitivity (qPCR) of the applied molecular diagnosis technique, the viral load carried by the material used (nasal swab, lung tissue sample, trachea sample), whether the animals being seropositive or in their convalescence period and the fragility of the agent.
163 NS strains obtained in this study were detected to be in a close genetic relation with some isolates in China, Turkey, Japan, the USA and South Korea and were located in BPIV3 genotype C. Besides, when this strain was compared to the isolates obtained in other studies in Turkey, Albayrak et al. (2019) found that it was 99.68% similar to the isolate (MH357343) they found in their study in Samsun and Timurkan et al. (2019) 97.99% similar to the one they found in their study in Erzurum. In accordance with this information, in our study, we supported the fact that BPIV3 genotype C was in circulation in cattle populations around Turkey. This study is the first one on antigenic and molecular detection and genetic examination of BPIV3 in south Turkey.
The strain we obtained in our study showed similarities to the isolates (HQ530153, KU198929, KT071671) found by Zhu et al. (2011) and Wen et al. (2012) in China at a rate of 99.2%, to the ones (LC000638, LC040886) obtained by Konishi et al. (2014) in Japan at rates of 96.62% and 97.31% respectively, to the virus (JX969001) isolated by Oem et al. (2013) in South Korea at a rate of 97.31% and to the strains (KJ647285, KJ647287, KJ647289) isolated by Neill et al. (2015) in the USA at rates of 97.65%, 98% and 80.45% respectively. On the other hand, it had a 79.22% genetic similarity with the strain (KP757872) isolated by Sobhy et al. (2017) in Egypt. The genetic similarity of the strain obtained in our study to SF-4 was accepted as the reference strain (AF178655) is 82.12% Bailley (2000).
During the studies performed on the antigenic detection of BPIV3 by DIF test, the prevalence varied between 9.8% and 41.5% (Alkan et al. 2000; Gençay and Akça 2004; Delgado et al. 2005; Çeribaşı et al. 2012; Çeribaşı et al. 2014; Maidana et al. 2012; Saeed et al. 2016; Kamdi et al. 2020). In this study, the positivity rate was found lower than those in the other studies. This result was believed to have occurred due to conscious breeding in sampling area, improved veterinarian services, common vaccination applications and better struggling with infections. In preventing BPIV3 infection, mucosal immunity is in the foreground compared to systemic immunity and while mucosal immunity plays a role in preventing the infection and decreasing the dispersion, systemic immunity allows an occurring infection to proceed more slightly (Elenkumaran 2013; Maclachlan et al. 2017). In accordance with this information, the fact that the sampled animals had strong mucosal immunity, they were seropositive or they had maternal antibodies against the agent could be considered as other biological agents causing low prevalence rate.
In our study, due to the fact that immune response was not sufficient, the diagnosis of the agent could be performed in animals whose nasal swab samples were taken to be detected in terms of BPIV3 in molecular and antigenic ways. Although clinical symptoms were seen, in animals whose BPIV3 viral genome could not be detected, a respiratory system infection caused by other viral, bacterial or parasite pathogens or a clinical picture dependent on secondary infections occurring after BPIV3 infection was believed to have formed. In addition, in sampled animals whose clinical symptoms subsided, the reason why the agent could not be detected was thought to be the fact that the disease did not contain the agent as it was in convalescence period or the animals were in convalescence period since 1-2 weeks passed after they showed severe symptoms. On the other hand, detection of the agent could not be performed on conjunctival swab samples as it showed affinity against respiratory tract cells where NANA receptor molecules such as BPIV3 pneumocytes, bronchial cells and trachea epitheliums were abundant (Maclachlan et al. 2017). In addition, because the agent did not have viremia period or it was too short, it was considered natural not to be able to detect the virus in leukocyte samples.