Serological survey on infectious diseases of a White yak herd in the Gansu Province

H.E. Geilhausen

Yak and Camel Foundation, P.O. Box 10, D-25359 Krempe, Federal Republic of Germany

Summary

From a 330 head White yak herd, 50 (approximately 15%) blood samples for serum preparation were taken to determine the immune status of the animals in relation to viral and bacterial antigens. Viral antigens—Bovine Herpes Virus 1 (BHV1), Bovine Viral Diarrhoea/Mucosal Disease (BVD/MD), Parainfluenza 3 (PI3) and Bovine Leucosis (BLV)—the most important infectious diseases of cattle, were used. To determine typical bovine bacterial antibodies, the following antigens were used: Brucella spp., Chlamydia spp., Coxiella burnetii, Salmonella spp. and Paratuberculosis. Negative results were obtained for Bovine Leucosis, Brucella spp., Salmonella spp. and Paratuberculosis. A positive antibody status was demonstrated in 96% of the samples for PI3, 34% for BHV1, 18% for BVD/MD, 24% for Chlamydia and 2% for Coxiella burnetii. Surprisingly, the herd seemed to be negative for Brucella spp, which is quite common in yak and humans in the Himalayas. The proportion of positive cases for BHV1 and PI3 were comparable to cattle in other regions of the world. The incidence of Chlamydia was relatively high. Compared to cattle in other countries of intensive breeding where the proportion of positive BVD/MD are in the range of 70–80%, on average, the 18% positive animals in the present study was quite low.

Keywords: Serological survey, viral and bacterial antigens, White yak

Introduction

Serological procedures constitute an important basic methodology for the study of viral and bacterial diseases and of their causal agents. A number of studies on parasitic diseases have been conducted on the yak (Joshi and Pradhan 1977; Biwas et al. 1994; Liu 1994; Rangarao et al. 1994; Jiang et al. 1997), but the references on viral and bacterial diseases are very limited and even these do not have local experimental data, but are citations of results from elsewhere (Joshi 1976; Joshi et al. 1997; Lensch and Geilhausen 1997). Even the standard books on yak from Zhang (1989) and Cai (1990) do not refer to infectious diseases. The handbook of Lensch (1996) contains a short survey on parasitic infestations and infectious diseases of viral and bacterial origin.

This paper reports results of physical examination of blood serum samples from White yak with a focus on viral and bacterial antigens, which are common in bovine species.

Materials and methods

Animals, sample collection and preparation

From a 330 head White Yak herd in Tianzhu County (Gansu Province, P.R. China), 50 blood samples (approximately 15%) were randomly taken by venapuncture under aseptic conditions. The animals were of different ages and both males and females were represented.

After blood clotting at 4°C the samples were centrifuged for 10 minutes at 3000 rpm for serum preparation. The serum samples were stored in plastic tubes at –20°C until analysis.

Antigens

Viruses and bacteria were used as test antigens, following procedures routinely applied in a German diagnostic laboratory for bovine serum samples. Specifically viral antigens Bovine Herpes Virus 1 (BHV1), causing Infectious Bovine Rhinotracheitis (IBR) and Infectious Pustular Vulvovaginitis (IPV), Bovine Viral Diarrhoea/Mucosal Disease (BVD/MD), Parainfluenza 3 (PI3) and Bovine Leucosis (BLV), were used. To determine typical bovine bacterial antibodies Brucella spp., Chlamydia spp., Coxiella burnetii (causing Q (query) fever in ruminants and human), Salmonella spp. and Paratuberculosis were used.

Test methods

To detect positive antibody levels, depending on the antigens, different techniques were used. Enzyme Immune Assays (EIA) were applied to determine antibodies against BHV1, BVD/MD and Coxiella burnetii; Slow Agglutination Test (SAT) was used for Brucella and Salmonella spp. Serum Neutralisation Test (SNT) was used to detect Parainfluenza 3, Agar Gel Immune Diffusion (AGID) for BVL and Complement Fixation Test (CFT) for Chlamydia.

Results and discussion

Four of nine bovine antigens involved in the survey, Bovine Leucosis, Brucella spp., Salmonella spp. and Paratuberculosis (Johnes Disease), did not show any positive antibody levels. The results are summarised in Table 1.

Table1. Results of the serological survey.

Antigens1	Positive		Negative		Suspicious		Not analysable
	No.	%	No.	%	No.	%	No.	%
BHV1	17	34	32	64	1	2	0	0
BVD/MD	9	18	38	76	3	6	0	0
PI3	48	96	0	0	2	4	0	0
Bovine Leukosis	0	0	50	100	0	0	0	0
Brucella	0	0	50	100	0	0	0	0
Chlamydia	12	24	34	68	1	2	3	6
Coxiella burnetii	1	2	49	98	0	0	0	0
Salmonella	0	0	50	100	0	0	0	0
Paratuberculosis	0	0	50	100	0	0	0	0
1. BHV1 = Bovine Herpes Virus 1; BVD/MD = Bovine Viral Diarrhoea/Mucosal Disease; PI3 = Parainfluenza 3.

A positive antibody status could be demonstrated in 96% of the samples for PI3, 34% for BHV1, 18% for BVD/MD, 24% for Chlamydia and 2% for Coxiella burnetii.

Parainfluenza viruses are found worldwide in animals and humans. Under normal conditions, PI3 infections in bovine species are clinically unapparent. They play an important role in USA and Europe as key agents of Shipping Fever and Crowding Disease within the so-called 'Bovine Respiratory Disease (BRD) complex'. The BRD complex is a factorial disease and occurs particularly when animals are in stress situations, e.g. during transportation and crowding. Rolle and Mayr (1978) reported positive titres of PI3 in 60–90% of cattle in USA and Europe. Similar values could be observed in humans.

The positive percentage of 34% for BHV1 seems comparable to cattle in other regions of the world. Although IBR/IPV is a separate disease clinically, the infection is very frequently associated with the BRD complex.

Compared to cattle populations in other countries with intensive management where the incidences of BVD/MD are 70–80%, on average, the 18% incidence in the present study was low. For western Germany, as far back as 1964, up to 72% of the cattle examined showed positive BVD/MD titres (Rolle and Mayr 1978).

The incidence rate (24%) for Chlamydia was relatively high. However, there were no figures available in literature, except personal communications, on the incidence of Chlamydia infections in the yak. As in cattle and other species, the focus in yak seems to be the genital tract. The infection affects conception/nidation and can cause enzootic abortions in yak.

The finding of a clearly positive reaction in one animal for Coxiella burnetii, a rickettial infection, which is tick-borne and is the causal agent of Q fever in ruminants and humans, was interesting.

It was, however, surprising that the herd was negative for Brucella spp., which is usually common in yak and humans in the Himalayan region. Detailed survey of Brucellosis cases in various animal species were carried out in Nepal (Joshi 1976; Payakural and Mishra 1977). Up to 29% positive reactions were observed in yak and yak hybrids. Brucellosis has also been confirmed in yak in the former Soviet Union (Schley 1967). Anon (1965) demonstrated the problems of Brucellosis as zoo-anthroponosis in Mongolia. In human populations with contact to a yak herd, 50–70% of the tested persons showed a positive reaction for Brucella spp.

From the results of the serological survey of the White yak herd in Tianzhu, mainly respiratory and, to some extent, genital infections seem to play a significant role. However, it must be emphasised that a single study such as this provides only a snapshot at a point in time and shows only the situation of the day the serum samples were taken. To assess the real situation, at least two serum samples, taken 3–4 weeks apart, have to be analysed to determine sero-conversion.

Acknowledgements

The author is most grateful to Dr Dieter Klein and his colleagues at the Landesuntersuchungsamt Rheinland-Pfalz, Fachbereich Tiermedizin, D-56073 Koblenz, Germany for technical support.

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