Caprine herpesvirus-1 abortion storm in a goat herd in Quebec

Abstract

Numerous abortions were reported on a Quebec goat farm, and caprine herpesvirus-1 (CapHV-1) was confirmed by PCR in several tissues from 3 aborted fetuses. This is the first report of CapHV-1 in Canada. Practitioners and diagnosticians must consider this disease when making a differential diagnosis for caprine abortion.

A herd of 80 does on a mixed-breed goat farm in Quebec, with no previous history of reproductive problems, experienced an abortion storm. During the kidding period of January–February 2002, 50% of the does had late term abortions or gave birth to stillborn kids. When there were twins, often one was alive and the other dead at birth. Goats showed no clinical signs prior to abortion. The last animal to be introduced into the herd, in May 2001, was a buck. It was kept in an individual pen and had no contact with the other goats. No significant health problems were reported in its herd of origin in Alberta. Some goats from the Quebec herd were brought to an animal fair in July 2001 and may have had contact with other goats at that time.

Three late-term aborted goat fetuses from 3 separate litters and the placenta from one (fetus B) were submitted for necropsy to the Faculté de médecine vétérinaire de l’Université de Montréal. All fetuses were moderately autolyzed. In fetus A, several pinpoint white foci, 1 to 2 mm in diameter, were disseminated in the lungs and liver. Pulmonary congestion was present in fetus C. No other gross lesions were observed. Samples of brain, tongue, skeletal muscles, heart, lung, thymus, liver, spleen, kidney, abomasums, and placenta were fixed in 10% neutral-buffered formalin and processed routinely for histological examination. All sections were stained with hematoxylin-phloxin-saffron (HPS). The following stains, Gram, Gomori-methenamine-silver (GMS), Gimenez, and Whartin-Starry, were used on selected sections. Frozen samples of thymus, lung, liver, spleen, and kidney were tested for bovine viral diarrhea virus (BVDV), bovine herpesvirus-1 (BHV-1), and leptospires, using a direct (BVDV, BHV-1) or indirect (leptospires) fluorescent antibody test (FAT). Samples of gastric contents, lung, liver, kidney, and placenta were sent for tents, routine bacteriological culture. Gastric contents, placenta, and liver were cultured for Campylobacter spp.

Microscopic examination revealed similar lesions in all animals. Multiple, small, randomly distributed necrotic foci were observed in the liver, lung, and thymus, and, to a lesser degree, in the spleen, kidney, and abomasal mucosa (Figures 1 and 2). Lesions were characterized by areas of coagulation necrosis, with minimal or no inflammation. In and around some necrotic foci, especially in the thymus, several intranuclear acidophilic inclusion bodies were present in parenchymal or epithelialreticular cells (Figure 2 insert). A mild neutrophilic reticular arteritis and periarteritis was present in the placenta (fetus B). No bacteria or fungi were revealed by the special stains.

Figure 1.

Liver; fetus A. Multiple necrotic foci are randomly distributed in the parenchyma. Hematoxylin-phloxin-saffron stain 40×.

Figure 2.

Thymus; fetus A. Large coagulative necrotic foci are found in some lobules. HPS. 40×. Insert: Acidophilic, intranuclear viral inclusions in some epithelial-reticular cells. nuclear Hematoxylin-phloxin-saffron stain 200×.

Tissues were positive by the FAT for BHV-1 and negative for leptospires and BVDV in all 3 fetuses. No significant bacteria were isolated and Campylobacter spp. were not found. An immunoperoxidase test (Prairie Diagnostic Services, Saskatoon) for Chlamydophila abortus done on slides of liver and spleen was negative.

Paraffin-embedded blocks of thymus, lung, liver, and spleen were sent to the Colorado Veterinary Diagnostic Laboratories for detection of caprine herpesvirus-1 (CapHV-1) by the polymerase chain reaction (PCR) technique. A reagent that releases DNA (GeneReleaser; BioVentures, Murfreesboro, Tennessee, USA) was used to extract DNA from unstained slides. Caprine herpesvirus-1 DNA was detected by PCR, using primers designed to amplify the amino terminus of the glycoprotein C gene. Amplification products were separated by electrophoresis in 1.5% agarose gels and visualized under ultraviolet light after being stained by ethidium bromide. Tissues from an aborted fetus (provided by Dr. Bill Layton, Michigan State University) served as a positive control. Negative control consisted of double distilled water (ddH₂O).

A band of approximately 182 base pairs (bp) was visualized in DNA preparations from different fetal tissues of animal C. Amplification products were not found in DNA preparations from tissues of fetuses A and B. Based on these results, a diagnosis of CapHV-1 abortion was made.

A seroneutralization test has been developed at the Institut National de Recherche Scientifique-Institut Armand-Frappier (Laval, Québec), using a CapHV-1 strain provided by the American Type Culture Collection (ATCC). Culture medium containing 100 TCID₅₀ of CapHV-1 was placed in contact with serum dilutions from 1 to 2 and 1 to 1024. After a 2-hour period, the mixture was incubated at 37°C for 4 to 5 d in the presence of calf testicle cells. Cells were then examined using a light microscope. The positive threshold of the test was established at 1 to 8.

All animals in the herd were tested. The sera of all does that had aborted and were still in the herd were positive for CapHV-1, with titers ranging from 1 to 24 and 1 to 256. Two of a total of 4 bucks were positive (1 to 192 and 1 to 256) and almost all kids from positive does were also positive. Fifteen kids were from 1 of the seropositive bucks; of these, 14 were positive.

Many infectious and noninfectious causes of abortion have been reported in goats. The most important infectious abortifacient agents in goats in North America include Chlamydophila abortus, Coxiella burnetii, Toxoplasma gondii, and Listeria monocytogenes (1). Caprine herpesvirus-1 (CapHV-1) has rarely been reported to cause abortion in goats. This virus is closely related to other ruminant α-herpesviruses, especially -BHV-1. Over the last 3 decades, infection by CapHV-1 has been reported in many countries, including the USA, but, to the best of our knowledge, not in Canada (2,3). Natural outbreaks of the disease are apparently rare even though seropositivity has been detected in many countries, showing that the virus is widespread (2). The virus appears to be species-specific, although antibodies to CapHV-1 have been detected in an ibex (Copra ibex) ) (2). As well, calves and lambs experimentally infected with CapHV-1 showed seroconversion, generally without clinical signs (2,4). Infections with CapHV-1 have been associated with late term abortions and gastroenteric and respiratory disease in 1- to 2-week-old kids (2,3,5). Infection in adult goats is generally subclinical, although vulvovaginitis or a balanoposthitis may develop (2). Rarely, pulmonary lesions have been reported in does (2).

The lesions observed in our case were characteristic of spontaneous CapHV-1-induced abortions (3). The reason for the negative PCR results for 2 of the 3 fetuses remains unknown. Possible reasons include a sampling problem (tissue with no viral DNA or with amounts below the test’s detection threshold) or interference with PCR enzymes, the samples’ nucleic acids, and other reagents by inhibitors present in the tissue extract. The positive FAT for BHV-1 in all 3 fetuses is probably due to the cross-reactivity of BHV-1 and CapHV-1 with this method (3). Seroconversion for CapHV-1 in all goats that aborted by the seroneutralization test is highly indicative that these animals were really infected by CapHV-1. It has been reported that BHV-1 causes only mild clinical signs in experimental infections of goats (4).

The source of infection remains uncertain as, in the recent past, no new animal had been introduced into the herd nor had any member of the herd travelled outside the farm. However, as with other α-herpesviruses, -CapHV-1 can remain latent in the trigeminal ganglia, other tissues (nose, vagina), or both, for a long time and be reactivated by stress or immunosuppression (4,6). Therefore, latently infected goats or bucks may have been present in the herd for many months or even years.

Although CapHV-1 has never been reported before in Canada, this may have been due to misdiagnosis. One study done in 1984 on the prevalence of some bovine viruses in the goat and sheep population of Quebec reported that 11 goat farms had serological evidence of BHV-1 infection (7); however, serological testing was done by IFAT, and CapHV-1 has been shown to cross-react with BHV-1 by this method (3). In fact, a study performed in 1985 on a similar population showed no BHV-1-infected goat farms in Quebec when testing was done by seroneutralization, which is a more virus- specific test (8). It could be hypothesized that the antibodies to BHV-1 demonstrated in goats in the 1984 study really indicated a CapHV-1 infection.

A CapHV-1 inactivated autovaccine has been produced and proved to fully protect the animals against a CapHV-1 challenge (9). However, as the disease caused by CapHV-1 seems relatively rare and sporadic, the pertinence of developing a commercial vaccine against this agent is questionable. Animals seem to develop a good humoral immunity; in fact, the producer reported no abortion during the following kidding period (April–May).

In conclusion, practitioners and diagnosticians must be aware of the presence of CapHV-1 in Canada and include this agent in their differential diagnoses when faced with abortions in goats.