Spontaneous human herpes virus type 1 infection in a chinchilla (Chinchilla lanigera f. dom.)

How Host Specific Are Herpesviruses? Lessons from Herpesviruses Infecting Wild and Endangered Mammals

Herpesviruses are ubiquitous and can cause disease in all classes of vertebrates but also in animals of lower taxa, including molluscs. It is generally accepted that herpesviruses are primarily species specific, although a species can be infected by different herpesviruses. Species specificity is thought to result from host-virus coevolutionary processes over the long term. Even with this general concept in mind, investigators have recognized interspecies transmission of several members of the Herpesviridae family, often with fatal outcomes in non-definitive hosts-that is, animals that have no or only a limited role in virus transmission. We here summarize herpesvirus infections in wild mammals that in many cases are endangered, in both natural and captive settings. Some infections result from herpesviruses that are endemic in the species that is primarily affected, and some result from herpesviruses that cause fatal disease after infection of non-definitive hosts. We discuss the challenges of such infections in several endangered species in the absence of efficient immunization or therapeutic options.

Management of Ocular Human herpesvirus 1 Infection in a White-faced Saki Monkey (Pithecia pithecia)

A 20-y-old male intact white-faced saki monkey (Pithecia pithecia) presented with an acute ocular disease of the right eye. Clinical signs included periocular swelling, conjunctivitis, and anisocoria with a miotic right pupil. Conjunctival swabs were positive for Human herpesvirus 1 (HHV1) according to PCR amplification with sequencing. Initial clinical signs resolved with supportive treatment, and the animal was managed chronically by using acyclovir (5 mg/kg PO twice daily) during flare-ups. After more than 2 y, the progression of clinical disease led to enucleation of the right eye. At 2 mo after surgery, acute presentation of severe neurologic signs, including ataxia and blindness, resulted in euthanasia. Histopathology, PCR analysis, and sequencing results were consistent with viral encephalitis due to HHV1; coinfection with Pithecia pithecia lymphocryptovirus 1 was identified. This report describes the first case of managed HHV1 infection in a platyrrhine primate and the first case of HHV1 in a white-faced saki monkey that was not rapidly fatal.

Herpes simplex encephalitis in a captive black howler monkey (Alouatta caraya)

An 18-month-old captive black howler monkey (Alouatta caraya) died after a 3-day history of neurologic signs. Gross findings at autopsy were limited to bloody, yellow, and foul-smelling intestinal contents. Histologically, there was extensive necrotizing meningoencephalitis predominantly in both cerebral hemispheres, and lymphohistiocytic, neutrophilic infiltrate expanded the subarachnoid and Virchow-Robbin space. In the most severely affected regions, neurons contained eosinophilic intranuclear inclusion bodies surrounded by a clear halo and margination of the chromatin. Electron microscopy of the affected cells revealed numerous intranuclear viral particles characteristic of herpesvirus. Immunohistochemically, neurons and glial cells in the affected regions were labeled with a monoclonal antibody against Human herpesvirus 1, and was confirmed by polymerase chain reaction.

Viral infections of rabbits

Viral diseases of rabbits have been used historically to study oncogenesis (e.g. rabbit fibroma virus, cottontail rabbit papillomavirus) and biologically to control feral rabbit populations (e.g. myxoma virus). However, clinicians seeing pet rabbits in North America infrequently encounter viral diseases although myxomatosis may be seen occasionally. The situation is different in Europe and Australia, where myxomatosis and rabbit hemorrhagic disease are endemic. Advances in epidemiology and virology have led to detection of other lapine viruses that are now recognized as agents of emerging infectious diseases. Rabbit caliciviruses, related to rabbit hemorrhagic disease, are generally avirulent, but lethal variants are being identified in Europe and North America. Enteric viruses including lapine rotavirus, rabbit enteric coronavirus and rabbit astrovirus are being acknowledged as contributors to the multifactorial enteritis complex of juvenile rabbits. Three avirulent leporid herpesviruses are found in domestic rabbits. A fourth highly pathogenic virus designated leporid herpesvirus 4 has been described in Canada and Alaska. This review considers viruses affecting rabbits by their clinical significance. Viruses of major and minor clinical significance are described, and viruses of laboratory significance are mentioned.

Encephalitis in a rabbit caused by human herpesvirus-1

CASE DESCRIPTION

An 8-month-old sexually intact male rabbit was examined because of a 2-day history of anorexia, epiphora of the left eye, bruxism, hypersalivation, and ataxia.

CLINICAL FINDINGS

Physical examination of the rabbit revealed bilateral conjunctivitis, hypersalivation, and severe signs of CNS dysfunction such as incoordination, intermittent myoclonic seizures, and opisthotonus. Results of hematologic and serum biochemical analyses revealed only lymphopenia, a relative monocytosis, and an increase in serum activity of creatine phosphokinase and serum concentration of total protein. Serum antibodies against Encephalitozoon cuniculi and Toxoplasma gondii were not detected.

TREATMENT AND OUTCOME

Despite IV administration of crystalloid fluids and treatment with antimicrobials, vitamin B complex, nutritional support, and prednisolone, the condition of the rabbit deteriorated; it was euthanized 7 days after admission. Histologic evaluation of brain tissue revealed lesions characteristic of severe, diffuse, nonsuppurative meningoencephalitis and a few large, eosinophilic, intranuclear inclusion bodies in neurons and glial cells. The DNA of human herpesvirus-1 was detected in the nuclei of glial cells, lymphocytes, and neurons by means of in situ hybridization. The rabbit's owner, who reported having had a severe labial and facial herpesvirus infection 5 days before the onset of clinical signs in the rabbit, was suspected to be the origin of infection for the rabbit.

CLINICAL RELEVANCE

Human herpesvirus-1 may be transmissible from humans to rabbits, and infection with this virus should be considered as a differential diagnosis in rabbits with CNS signs of disease.

Fatal human herpesvirus type 1 infection in a white-handed gibbon (Hylobates lar)

This report documents a case of spontaneous, fatal, and likely recrudescent human herpesvirus type 1 (HHV-1) infection in a captive white-handed gibbon (Hylobates lar) confirmed by polymerase chain reaction (PCR). An approximately 44-year-old, captive, female, white-handed gibbon with a history of recurrent conjunctivitis and occasional seizures became acutely weak, disoriented, and ataxic. A postictal state was suspected by caretakers and veterinary staff, and euthanasia was ultimately elected because of lack of clinical improvement with supportive care. No significant abnormalities were detected at necropsy. Histologically, sections of cerebrum and midbrain contained minimal to mild, multifocal lymphoplasmacytic meningoencephalitis with numerous intranuclear viral inclusions within astrocytes and some neurons. The presumptive diagnosis of HHV-1-induced encephalitis was strengthened by nested PCR amplification of a segment of the herpesvirus DNA polymerase gene. Sequences from this region have been found to be unique to each herpesvirus species, thus identifying HHV-1 as the likely etiologic agent in this case. Positive HHV-1 serology from several years before the terminal episode suggested that the disease was most likely due to recrudescence of latent HHV-1 infection.

Small mammal virology

Most viral infections in small mammals are transient and rarely produce clinical signs. When clinical signs do appear, they are often of a multifactorial etiology such as respiratory infection with Sendai virus and the bacteria M. pulmonis in rodents. Diagnosis is generally made based on clinical signs, while therapy involves treatment for concurrent bacterial infections and supportive care. Small mammals may carry zoonotic viruses such as LCMV, but natural infections are uncommon. Viral diseases are rare (or largely unknown) for hedgehogs, chinchillas, and prairie dogs, while no known naturally occurring, clinically relevant viral diseases exist for gerbils and sugar gliders. This article is intended to aid the clinician in identifying viral infections in small mammals and to help determine the significance each virus has during clinical disease.