Laboratory diagnosis of ruminant abortion in Europe

53 Pages·2017·1.75 MB·English

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Year: 2014
Laboratory diagnosis of ruminant abortion in Europe
Borel, N ; Frey, C F ; Gottstein, B ; Hilbe, M ; Pospischil, A ; Franzoso, F D ; Waldvogel, A
Abstract: Abortion in ruminants is a major cause of economic loss worldwide, and the management
and control of outbreaks is important in limiting their spread, and in preventing zoonotic infections.
Given that rapid and accurate laboratory diagnosis is central to controlling abortion outbreaks, the
submission of tissue samples to laboratories offering the most appropriate tests is essential. Direct
antigen and/or DNA detection methods are the currently preferred methods of reaching an aetiological
diagnosis, and ideally these results are confirmed by the demonstration of corresponding macroscopic
and/or histopathological lesions in the fetus and/or the placenta. However, the costs of laboratory
examinations may be considerable and, even under optimal conditions, the percentage of aetiological
diagnoses reached can be relatively low. This review focuses on the most commonly occurring and
importantabortifacientpathogensofruminantspeciesinEuropehighlightingtheirepizooticandzoonotic
potential. Theperformancecharacteristicsofthevariousdiagnosticmethodsused,includingtheirspecific
advantages and limitations, are discussed.
DOI: https://doi.org/10.1016/j.tvjl.2014.03.015
Posted at the Zurich Open Repository and Archive, University of Zurich
ZORA URL: https://doi.org/10.5167/uzh-95873
Journal Article
Accepted Version
Originally published at:
Borel, N; Frey, C F; Gottstein, B; Hilbe, M; Pospischil, A; Franzoso, F D; Waldvogel, A (2014). Labo-
ratory diagnosis of ruminant abortion in Europe. Veterinary Journal, 200(2):218-229.
DOI: https://doi.org/10.1016/j.tvjl.2014.03.015
1 Commissioned Review
2
3 Laboratory diagnosis of ruminant abortion in Europe
4
5 Nicole Borel a,*, Caroline F. Frey b, Bruno Gottstein b, Monika Hilbe a, Andreas Pospischil a,
6 Francesca D. Franzoso a, Andreas Waldvogel a
7
8 a Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Switzerland
9 b Institute of Parasitology, Vetsuisse Faculty, University of Berne, Switzerland
10
11 * Corresponding author. Tel.: [phone].
12 E-mail address: [email protected]
13
14 Abstract
15 Abortion in ruminants is a major cause of economic loss worldwide, and the
16 management and control of outbreaks is important in limiting their spread, and in preventing
17 zoonotic infections. Given that rapid and accurate laboratory diagnosis is central to
18 controlling abortion outbreaks, the submission of tissue samples to laboratories offering the
19 most appropriate tests is essential. Direct antigen and/or DNA detection methods are the
20 currently preferred methods of reaching an aetiological diagnosis, and ideally these results are
21 confirmed by the demonstration of corresponding macroscopic and/or histopathological
22 lesions in the fetus and/or the placenta. However, the costs of laboratory examinations may be
23 considerable and, even under optimal conditions, the percentage of aetiological diagnoses
24 reached can be relatively low. This review focuses on the most commonly occurring and
25 important abortifacient pathogens of ruminant species in Europe highlighting their epizootic
26 and zoonotic potential. The performance characteristics of the various diagnostic methods
27 used, including their specific advantages and limitations, are discussed.
28
29 Keywords: Abortion; Infectious; Ruminant; Diagnosis; Zoonotic; Europe
30 Introduction
31 An increase in the number of spontaneous abortions in a herd or flock is a dramatic
32 event for the farmer involved, and a range of epizootic and/or zoonotic diseases, or even
33 emerging diseases, may be the cause. In such situations farmers, along with their veterinary
34 practitioners, and potentially state veterinarians, expect rapid reliable results from diagnostic
35 veterinary laboratories, a process that is not always easily achieved. While a plethora of
36 pathogens can cause abortion in ruminants, there is no single diagnostic procedure that can be
37 used to identify these, and in some circumstances the infectious event triggering an abortion
38 may precede it some weeks or months so that evidence of the presence of the pathogen may
39 be obliterated by autolysis. By this time it may no longer be possible to demonstrate a rise in
40 maternal antibody indicative of recent infection. Since attempting to rule out all the possible
41 causes of abortion, can prove costly, diagnostic laboratories primarily focus on the most likely
42 aetiologies and those with zoonotic potential.
43
44 This review assesses the most important viral, bacterial, fungal and protozoal causes
45 of abortion in cattle, sheep and goats in an industrialised European country (Switzerland),
46 focusing on the methods used to reach a diagnosis and highlighting protocols that optimise
47 pathogen detection. The information presented will be of interest to laboratory diagnosticians,
48 as well as veterinary practitioners and state veterinarians. An overview of the infectious
49 abortifacients discussed is given in Table 1.
50 Viral causes
51 Bovine herpesvirus type I
52 Bovine herpesvirus 1 (BoHV-1) infections remain a major cause of abortion, venereal
53 and respiratory disease in ruminants in countries where this pathogen has not been eradicated
54 (Kirkbride, 1992). Latency with recurrent infection is typical for infection with these viruses:
55 during latency the virus survives within cells without causing clinical signs, and upon
56 reactivation, repeated abortion may occur (Nandi et al., 2009). Given that virus is shed during
57 reactivation, an infected animal remains a source of infection for in-contact herd-mates. For
58 this reason, European countries such as Austria, Denmark, Finland, Sweden, Italy,
59 Switzerland and Norway have eradicated this economically significant infection.
60
61 BoHV-1 abortion can be diagnosed by demonstrating the presence of the virus in the
62 aborted fetus and, in countries free of the virus, specific antibodies in maternal sera. PCR is
63 currently the most sensitive method of identifying the virus in fetal tissues, particularly the
64 liver (Crook et al., 2012). In endemic regions, serology is of little value in establishing a
65 diagnosis of BHV-1 abortion, as maternal infection may precede abortion for up to two
66 months (Kennedy and Richards, 1964). Thus by the time abortion occurs, maternal antibody
67 levels may have already peaked so that demonstrating a rise in specific antibody levels may
68 no longer be possible. The only grossly visible evidence of BoHV-1 infection in the fetus is
69 subtle multifocal necrosis, particularly of the liver. The fetus is typically autolysed on
70 expulsion with haemoglobin-tinged fluid in its body cavities. Microscopic examination of the
71 liver and adrenal glands may facilitate the identification of necrotic foci with attendant
72 leucocyte infiltration (Schlafer and Miller, 2007). When such lesions are observed, further
73 tests for BoHV-1 infection are recommended, even in regions free of infection.
74
75 Pestiviruses
76 Bovine viral diarrhoea virus (BVDV) and Border Disease virus (BDV) belong to the
77 genus pestivirus of the family Flaviviridae, are single-stranded RNA viruses, and exist as
78 both non-cytopathic and cytopathic biotypes, respectively. An animal may remain persistently
79 infected with a non-cytopathic biotype if exposed during the first trimester of pregnancy
80 (Bachofen et al., 2008; Hilbe et al., 2009). In a retrospective study of bovine abortion in
81 Switzerland between 1986 and 1995, 22/223 (9.9%) were positive for BVDV infection on
82 immunohistochemistry, the second most common cause of infectious abortion after Neospora
83 caninum infection (Reitt et al., 2007). Macroscopically visible brain malformations such as
84 porencephaly, hydranencephaly and cerebellar hypoplasia may result from fetal infection
85 (Moening, 1990; Nettleton and Entrican, 1995; Grooms, 2004). However, since such lesions
86 may also result from infection with other viruses, exposure to toxic compounds or genetic
87 disorders, and since fetal infection with BVDV does not necessarily produce morphological
88 alterations, demonstration of the presence of virus is required to confirm the diagnosis.
89
90 BDV can cause infertility, abortion, stillbirth and the birth of ‘hairy-shaker’ lambs
91 depending on the time of fetal infection. The name ‘Border Disease’ was coined as the disease
92 was first reported in the border region between England and Wales (Sawyer, 1992). In
93 persistently-infected sheep the non-cytopathic virus induces histologically visible myelin
94 deficiency in the CNS, resulting in tremor and an increase or enlargement in the number of
95 primary hair follicles. These ‘hairy-shaker’ animals are persistently infected with virus
96 (Nettleton, 1987; Sawyer, 1992; Nettleton and Entrican, 1995; Nettleton et al., 1998), and
97 antigen can be found in smooth muscle cells (e.g. of blood vessels), epithelial cells (e.g. of
98 hair root sheath), lymphocytes, neurons and glial cells using immunohistochemistry
99 (Brodersen, 2004; Saliki and Dubovi, 2004; Sandvik, 2005; Hilbe et al., 2007a,b).
100
101 Persistent infection with either BVDV or BDV is best confirmed by
102 immunohistochemistry and RT-PCR on skin. Samples from the ear are typically used for this
103 purpose and no fixation or pre-treatment is required. When a whole aborted fetus is available,
104 snap frozen samples of skin, tongue, and thyroid gland are used for immunohistochemistry
105 (Brodersen, 2004; Sandvik, 2005; Hilbe et al., 2007a, b). Carrying out an ELISA on skin or
106 tissue such as thyroid gland from aborted bovine fetuses gives false positive results, perhaps
107 due to the effects of autolysis.
108
109 BVDV or BDV may cross the placenta in persistently infected animals or during the
110 viraemic phase in an acutely infected animal. Infection may go unnoticed as clinical signs
111 may be absent or very mild during acute infection with BVDV and the impact on the fetus
112 depends largely on the stage of fetal development at the time of infection: fetal resorption,
113 abortion, mummification or malformation such as cerebellar hypoplasia or porencephaly may
114 result (Brownlie et al., 1987; Moening, 1990; Nettleton and Entrican, 1995; Grooms, 2004).
115 Infection with non-cytopathic BVDV at approximately 40 to 120 days gestation can induce
116 immunotolerance in the fetus to the infecting virus strain (Brownlie et al., 1987; Brock, 2003;
117 Grooms, 2004; Bachofen et al., 2008), ultimately resulting in persistent viraemia in these
118 animals. By approximately 150 days gestation the fetus is sufficiently immunocompetent to
119 eliminate the infection (Nettleton and Entrican, 1995; Brock, 2003; Grooms, 2004). With
120 BDV ovine fetuses become persistently infected between approximately day 60 and 80 of
121 gestation (Nettleton, 1987; Sawyer, 1992; Braun et al., 2002).
122
123 As abortion due to BVDV infection is often the result of one or more persistently
124 infected animals in the herd, control measures must be directed at identifying and eliminating
125 such individuals (Presi and Heim, 2010; Presi et al., 2011). Since pestiviruses are not strictly
126 species-specific, sheep may infect cattle and vice versa (Carlsson, 1991; Sawyer, 1992; Braun
127 et al., 2002). This factor should therefore be considered in herds where no obvious source of
128 infection can be detected. Zoonotic infections with pestiviruses have not been reported.
129
130 Teratogenic viruses
131 When an increased number of abortions with attendant malformations of the central
132 nervous (CNS) and musculoskeletal systems occur, infection with members of the
133 Orthobunyavirus group or Bluetongue virus (BTV) must be considered. Since these viruses
134 are vector-born their geographic range is limited by the habitat of competent vectors.
135 Nevertheless, both Schmallenberg (SBV) and Bluetongue virus have both recently caused
136 epizooties with consequent massive economic loss in Europe, an area where infections with
137 these viruses had previously been unknown: an important reminder of the importance of the
138 ongoing surveillance of livestock for emerging diseases.
139
140 Schmallenberg virus is a novel Orthobunyavirus, belonging to the Simbu serogroup of
141 Shamonda/Sathuperi-like viruses. Following its initial detection in dairy cattle in North
142 Rhine-Westphalia in Germany in 2011, this virus infection spread rapidly across Europe: to
143 the Netherlands, Belgium, France, Germany, Italy, Luxembourg, Spain, Switzerland and the
144 UK. Schmallenberg virus RNA was also found in Culicoides spp. in Denmark and Belgium
145 (ProMED-Mail, 2012; Rasmussen et al., 2012). Infection may cause hyperthermia, decreased
146 milk production, and watery diarrhoea in adult cattle. Gross lesions in aborted, stillborn and
147 neonatal lambs, goat kids and calves include brachygnatia inferior, torticollis, kyphosis,
148 scoliosis, arthrogryposis, vertebral malformations with unilateral spinal muscle atrophy,
149 hydrancephaly, porencephaly, hydrocephalus, cerebellar hypoplasia and micromyelia
150 (Garigliany et al., 2012; Herder et al., 2012). The main histopathological changes in the CNS
151 are lympho-histiocytic meningoencephalomyelitis with glial nodules in the mesencephalon
152 and hippocampus in lambs and goats, and neuronal degeneration/necrosis in the brain stem of
153 calves. Myofibrillar hypoplasia is also reported in lambs and calves (Herder et al., 2012).
154
155 Since infection with other pathogens may result in comparable lesions, infection with
156 SBV requires confirmation by the demonstration of virus in the cerebrum and brain stem,
157 amniotic fluid and/or meconium (OIE, 2012). RT-qPCR is the standard method of detecting
158 SBV in lambs, kids and calves (Garigliany et al., 2012). To date, there is no evidence that
159 SBV is zoonotic (Garigliany et al., 2012). Schmallenberg virus is closely related to Akabane
160 virus (Hahn et al., 2012), and studies of the congenital abnormalities resulting from fetal
161 Akabane virus infection in cattle suggest that hydranencephaly and porencephaly develop
162 when infection occurs between 76 and 104 days of gestation. In contrast, arthrogryposis
163 results from infection at between 103 and 174 days of infection (Kirkland et al., 1988).
164 Evaluating the type of lesions caused by SBV might therefore be useful in estimating the time
165 infection is introduced into a naïve herd. However, more data from field cases and/or
166 experimental infections will be needed in order to fully characterise this recently emerged
167 disease.
168
169 Blue tongue virus belongs to the family Reoviridae, genus Orbivirus, and is usually
170 transmitted to domestic and wild ruminants by haematophagus insects of the genus Culicoides
171 (Maclachlan, 2011). The European strain BTV-8, which emerged in the summer of 2006, is
172 one of the most virulent, spreading rapidly through western and central Europe. Infection
173 resulted in significant infertility, early embryonic death, abortions and stillbirth, as well as
174 cerebral malformation (Dal Pozzo et al., 2009; Maclachlan et al., 2009; Wouda et al., 2009;
175 Saegerman et al., 2011; OIE, 2012). Hydrancephaly was described in calves and lambs at
176 necropsy, and brachycephaly with brachygnathia superior and cerebellar aplasia were also
177 found in lambs (Vercauteren et al., 2008; Williamson et al., 2010; Saegerman et al., 2011).
178
179 The CNS malformations caused by BTV infection have been linked to the particular
180 susceptibility of neuronal and glial progenitor cells to infection prior to their migration to the
181 cerebral cortex and sub-cortical white matter (Maclachlan et al., 2000, 2009). Thus, fetal
182 infection results in cyst formation and dilated ventricles following selective destruction of
183 undifferentiated glial cells (Dal Pozzo et al., 2009). CNS defects in bovine fetuses are most
184 severe if infection occurs prior to 130 days of gestation (Dal Pozzo et al., 2009), and their
185 severity is considered inversely proportional to the period of gestation at which infection
186 occurs (Waldvogel et al., 1992; Maclachlan et al., 2000). The extent of lesions may also be
187 determined by viral dose and virulence and/or by the genetic predisposition of the fetus
188 (Waldvogel et al., 1987; Maclachlan et al., 2009; Williamson et al., 2010). The CNS
189 malformations described in calves infected with serotype-8 in Europe were similar to those
190 reported following infection with serotypes elsewhere (Desmecht et al., 2008; Maclachlan et
191 al., 2009).
192
193 Bluetongue virus is not zoonotic, and a presumptive diagnosis can be confirmed by
194 RT-qPCR on fetal tissues (Toussaint et al., 2007; Vandenbussche et al., 2008). RT-qPCR and
195 sequencing have numerous advantages in terms of speed, sensitivity and specificity and are
196 the most extensively used diagnostic method by reference centres throughout Europe (Brito et
197 al., 2011; Zientara et al., 2012). Other non-viral causes of congenital malformation of the
198 CNS or musculoskeletal system in cattle include plant poisoning (James et al., 1994) and
199 genetic defects (Murphy et al., 2007).
200 Bacterial causes
201 Brucella spp.
202 Brucellosis causes significant losses due to abortion and infertility in ruminants, but is
203 also zoonotic resulting in persistent or ‘undulant’ fever with influenza-like symptoms and can