Seroprevalence of bovine viral diarrhoea virus, bovine herpesvirus 1 and bovine leukaemia virus in Iranian cattle and associations among studied agents

Abstract

Bovine viral diarrhoea virus (BVDV), bovine herpesvirus type 1 (BoHV1) and bovine leukaemia virus (BLV) are among the most important pathogens of dairy cattle which cause significant economic burden around the world. The aim of this study was to investigate seroprevalence and concurrent presence of antibodies against BVDV, BoHV1 and BLV in dairy cattle in Iran. A total of 882 animals were sampled and the presence of antibodies against BVDV, BoHV1 and BLV was determined by commercial Enzyme link immunosorbent assay (ELISA) kits. The overall BVDV, BoHV1 and BLV seroprevalence was 64.4%, 31.9% and 16.2%, respectively. The prevalence of antibodies against mentioned pathogens varied among different provinces studied. In addition, no correlation was observed between BLV seropositivity and either BVDV or BoHV1 seropositivity while there was a positive correlation between BVDV and BoHV1 seropositivity (P < 0.01). The results of the current study revealed that BVDV, BoHV1 and BLV infections are present in different regions of Iran and thus it seems necessary to implement control programmes to prevent further spread of mentioned pathogens. Moreover, it was demonstrated that a previous infection with either BVDV or BoHV1 might be a risk factor for future infection with BoHV1 or BVDV, respectively.

Keywords:

• seroprevalence
• bovine viral diarrhoea virus
• bovine herpesvirus type 1
• bovine leukaemia virus
• Iran

Introduction

Viral infectious diseases are known to contribute to significant damages in dairy cattle around the world. In this regard, bovine viral diarrhoea (BVD), infectious bovine rhinotracheitis (IBR) and enzootic bovine leukaemia (EBL) are considered among the most important diseases that play a part in economic losses of dairy cattle industry (chi et al. 2002; Nandi et al. 2009).

Bovine viral diarrhoea virus (BVDV), the causative agent of BVD, belongs to the family Flaviviridae. This virus has a worldwide distribution and develops various infections with different clinical manifestations including: fever, gastrointestinal lesions and diarrhoea. Infection of cattle during the early gestation period may lead to the birth of persistently infected (PI) calves which are of great importance in the epidemiology of BVDV infection. Moreover, it has been demonstrated that cattle infected with both BVDV and bovine herpesvirus 1 (BoHV1) are at higher risk of reproductive disorders (Biuk-Rudan et al. 1999). BoHV1 is a member of Herpesviridae family and infections caused by BoHV1, including IBR, are classified in the list B of World Organisation for Animal Health (OIE) notifiable diseases. BoHV1 is one of the major causes of the bovine respiratory disease complex (shipping fever) and can also develop other clinical syndromes such as abortion and infertility (Nandi et al. 2009). As BoHV1 is capable of developing latent infection, BoHV1-positive cattle can act as carriers and spread infection to other animals (Nandi et al. 2009). Bovine leukaemia Virus (BLV) is a retrovirus that develops lymphomas in dairy cattle and cause EBL. Development of persistent lymphocytosis (PL) occurs in 20–30% of the infected cattle but in some cases (1–5%), the infection leads to malignant lymphoma which has lethal consequences. Furthermore, it is possible that the infected cattle remain asymptomatic and spread infection to healthy individuals (Trono et al. 2001). The losses are not only attributed to death but also export limitation of semen and ova from serologically positive animals (Trono et al. 2001).

Coinfection, a status in which multiple pathogens infect an individual, is a frequent phenomenon among animals. According to Candela et al. (2009), coinfection is an important epidemiological factor which is not often considered in epidemiological studies. Concurrent infections can make an animal either more susceptible or resistance to future infectious diseases by influencing host immune responses to pathogens (Candela et al. 2009).

With approximately nine million head of cattle, Iran has one of the largest cattle populations in the Middle East. Since the most important step in a control programme is to identify infection in a population and considering the fact that little epidemiological data on the status of BVDV, BoHV1 and BLV infections are available for Iran, the present study aimed to determine the prevalence of antibodies against BVDV, BoHV1 and BLV, as well as the rate of concurrent seroprevalence of mentioned pathogens in dairy cattle in different provinces of Iran. Another purpose of this study was to investigate whether seropositivity for BVDV, BoHV1 or BLV is associated with the risk of seropositivity for the other pathogens.

Materials and methods

Previous studies in Iran have revealed that prevalence of BVDV, BoHV1 and BLV infection was 72.24%, 34% and 22.3%, respectively (Hazrati et al. 1976; Talebkhan Garoussi et al. 2009; Tolouei et al. 2009). The minimum required sample size was calculated as 746 based on the previous prevalence of IBR (34%), confidence level of 95% and precision of 3.4%. Samples were collected from each province depending on the population density of dairy farm in each province. Using random cluster sampling, blood samples were taken from dairy cattle throughout four provinces of Iran including: Khorasan (Kh), Chaharmahal Bakhatiari (CB), Sistan and Baluchestan (SB) and Semnan (Se). Samples were obtained from four big cities of each province. The cities in each sampled province were included as follow: Kh province: Mashad, Torbat-e Heydariyeh, Sarakhs and Birjand; CB province: Boroujen, Lordegan, Shahrekord and Farsan; SB province: Zahedan, Zabol, Iranshahr and Saravan; Se province: Semnan, Garmsar, Damghan and Shahrood.

Each city was divided into 2–5 sample districts of approximately equal areas that corresponded to one or more governmental veterinary organisation districts. Of the latter districts, 10–15 samples were randomly chosen for the study. Dairy farms from the interior of each district were chosen and animals were selected randomly. In large farms, 10–15 cows were bled; in small farms, all cows were bled until the predetermined sample size for that district was achieved. Between July 2006 and April 2007, a total of 882 female dairy cattle were bled in 40 sample districts in 16 cities of 4 provinces of Iran. The provincial distribution of chosen samples in this study was as follows: 290 (32.9%) animals to Kh (east and northeast), 94 (10.6%) dairy cattle to SB (east and southeast), 192 (21.8%) animals to CB (centre) and 306 (34.7%) dairy cattle to Se province (north-centre). In SB province, a lower number of animals were sampled due to lower population density of dairy cattle. Blood samples were centrifuged and sera were stored at –20°C until used.

Commercial Enzyme link immunosorbent assay (ELISA) kits were used to determine the presence of specific antibodies to BVDV (SVANOVA Biotech AB, Uppsala, Sweden), BoHV1 (SVANOVA Biotech AB, Uppsala, Sweden) and BLV (SVANOVA Biotech AB, Uppsala, Sweden). All procedures and interpretation of the results were according to the instructions of the manufacturer.

Descriptive statistics (i.e. frequencies and percentage) were used to calculate the prevalence of the anti-BVDV, BoHV1 and BLV immunoglobulins G (IgGs) in indigenous dairy cattle in four provinces of Iran. The true prevalence was calculated based on the formula described by Rogan and Gladen (1978).

The association of concurrent presence of antibodies was determined by chi-square test in the following groups: (1) BVDV and BoHV1 seropositive cattle (2) BVDV and BLV seropositive cattle (3) BoHV1 and BLV seropositive cattle. The data were analysed by PASW statistics 18.0 and P < 0.01 was considered significant.

Results

Anti-BVDV, BoHV1 and BLV antibodies were present in 570 (64.4%), 298 (31.9%) and 127 (16.2%) of examined dairy cattle, respectively. The spatial pattern of BVDV, BoHV1 and BLV seroprevalence varied among the studied provinces (Table 1). The prevalence and the correlation of concurrent presence of antibodies against two pathogens have been summarised in Table 2.

Table 1. Prevalence of IgG antibodies against BVDV, BoHV1 and BLV in four provinces of Iran.

	BVDV		BoHV1		BLV
Province	Number of seropositive animals	True prevalence (%)	Number of seropositive animals	True prevalence (%)	Number of seropositive animals	True prevalence (%)
Chaharmahal Bakhtiari	96	50.7	103	57.7	49	25.27
Khorasan	163	55.3	88	25.6	16	7.52
Semnan	228	74	72	21.7	45	15.84
Sistan and Baluchestan	83	89	35	32.9	17	17.9

Table 2. Prevalence and correlation of concurrent presence of antibodies against BVDV, BoHV1 and BLV.

Groups	Number of seropositive animals	Percentage of seropositive animals	P-value
BVDV + BoHV1	211	26.2	<0.01*
BVDV + BLV	85	12.1	0.04
BoHV1 + BLV	46	7	0.19

* P < 0.01 was considered significant.

Discussion

In the current study, we tried to provide more data on seroprevalence of BVDV, BoHV1and BLV and correlation of concurrent seropositivity with these pathogens in Iran. We found that the overall prevalence of antibodies against BVDV in cattle ranged from 50.7% to 89% among the four provinces studied. As vaccination against BVDV and BoHV-1 is not practised in Iran, the presence of these antibodies indicates a natural exposure to BVDV and BoHV-1. A previous serological study of industrial dairy cattle in Mashhad also confirmed that anti-BVDV antibodies are present in Iran with a prevalence of 72.25% (Talebkhan Garoussi et al. 2009). The prevalence obtained in this study was higher than those reported in other countries ranging from 11.46% to 41.4% (Mainar-Jaime et al. 2001; Yeşilbağ & Güngör 2008; Talafha et al. 2009; Nigussie et al. 2010). Based on the results of our study, prevalence of anti-BVDV IgG varied among different regions of Iran. This is similar to the findings of variation in seroprevalence of BVD among different states of Mexico (Solis-Calderon et al. 2005). These seroprevalence variations could be attributable to the following factors: population density, preventive measures to control diseases and age of animal (Mainar-Jaime et al. 2001). Former studies on camels and buffalos in Iran demonstrate that 19.7% of camels and 33.9% of buffalos have anti-BVDV antibodies (Hajikolaei et al. 2010; Raoofi et al. 2010). The higher prevalence of BVDV in cattle in comparison to camels and buffalos could rise from various reasons such as population density and different management practices.

In this study, the overall seroprevalence of IBR was 31.9% ranging from 21.7% to 57.7% in different provinces. Similarly, an earlier study in Iran revealed that 34% of sampled cattle were BoHV1 seropositive which may indicate BoHV1 infection is spreading at a constant rate due to lack of a control programme in Iran (Hazrati et al. 1976). The anti-BoHV1 antibodies have been identified in other parts of the world differing from 17.1% to 60.84% (Van Wuijkhuise et al. 1993; Achour & Moussa 1996; Yeşilbağ & Güngör 2008; Trangadia et al. 2010). In addition, Solis-Calderon et al. (2003) have shown that anti-BoHV1 antibodies could also differ among regions of the same country as is the fact in the current study. This variation could result from divergent factors such as breeding type, animal age and herd size (Mcdermott et al. 1997). About 16.2% of all animals tested for antibodies against BLV were BLV seropositive. The BLV seroprevalence in this study did not differ greatly in comparison to that (22.3%) reported by Tolouei et al. (2009) in Tehran province. The seroprevalence of BLV in our study (16.2%) was higher than those reported elsewhere ranging from 0% to 11% (Uysal et al. 1998; Meas et al. 2000a, 2000b). However, other seroepidemiological surveys have indicated that in some countries BLV seroprevalence might range from 28.6% to 36% (Schoepf et al. 1997; Trono et al. 2001; Murakami et al. 2011).

The positive association between BVDV and BoHV1 seropositivity could be, at least in part, the result from synergism in the pathogenesis of these pathogens. For example, BVDV and BoHV1 both can evade innate immune system by interfering in function of interferon (IFN) response factor 3 (IRF3), a transcription factor necessary for IFN promoter activation. This interference can lead to lower production of IFNs which play a vital role in the stimulation of innate immunity responses and prevention of viral infections (Srikumaran et al. 2007). Furthermore, both BVDV and BoHV1 can suppress adaptive immunity responses by mechanisms such as inhibition of leukocyte proliferation (Srikumaran et al. 2007). Similar risk factors and a common route of infection may also be considered as other possible reasons for the positive association between BVDV and BoHV1 seropositivity.

In the present study, no significant correlation between BLV seropositivity and either BVDV seropositivity or BoHV1 seropositivity was observed. One possible explanation, at least in part, is that BLV infection is not associated with impairment of normal immunological activities in infected animals (Cockerell et al. 1987). Moreover, in BLV seropositive cattle, but not in cattle with PL, cytokines related to Th1 responses are upregulated. This may cause stimulation of cell-mediated immunity and subsequent control of disease (Kabeya et al. 2001). It has also been shown that BLV-infected cattle can develop a non-specific stimulation of B lymphocytes in face of non-BLV antigens (Isaacson et al. 1998).

In conclusion, the results of the current study revealed that antibodies against BVDV, BoHV1 and BLV are present in the cattle population of Iran and thus it seems necessary to implement control programmes to prevent further spread of mentioned pathogens. Moreover, we found a positive correlation between BVDV and BoHV1 seropositivity which may demonstrate the importance of coinfection as an epidemiological factor. The significance of this concurrent seropositivity is due to the fact that dairy cows which are seropositive for both BVDV and BoHV1 are in higher risk of reproductive problems (Biuk-Rudan et al. 1999). However, further investigation is necessary to explore the association between BVDV, BoHV1 and BLV seropositivity.