Pseudorabies Virus (PRV) is a concern in animal health, particularly within livestock. First identified in 1902 by Hungarian veterinarian Aladár Aujeszky, this viral disease has historically impacted various animal species, especially swine. Globally, its economic implications for the swine industry have been substantial in regions where other major swine diseases are controlled.
Understanding Pseudorabies Virus
Pseudorabies Virus, also known as Aujeszky’s disease, is a DNA virus classified as Suid herpesvirus 1 (SHV-1) within the Herpesviridae family. This enveloped, double-stranded DNA virus is the sole serotype within its classification. Its natural host is swine, including both domestic and wild pigs.
PRV can infect many other mammals, considered secondary or “dead-end” hosts. These include cattle, sheep, goats, dogs, cats, and various wildlife like raccoons, opossums, and mink. In these secondary hosts, infection often leads to severe neurological signs and intense itching, explaining its common name, “Mad Itch.” This itching can be so severe that animals may self-mutilate.
Transmission and Clinical Manifestations
PRV primarily spreads through direct contact with infected animals, especially via nasal and oral secretions. The virus sheds in saliva and nasal discharges, facilitating its spread among animals in close proximity. Airborne transmission through aerosols is also a recognized route, with the virus capable of spreading over distances, sometimes many kilometers, under favorable conditions. Contaminated feed, water, and inanimate objects (fomites) like boots, clothing, and equipment can also transmit the virus indirectly.
Clinical signs vary by host species and age. In pigs, young piglets are vulnerable, often showing severe neurological signs such as trembling, incoordination, and seizures, with mortality rates potentially reaching 100% in those under two weeks old. Older pigs may show respiratory symptoms like coughing, sneezing, and nasal discharge, sometimes progressing to pneumonia. Reproductive issues, including abortions, stillbirths, and returns to estrus, are common in pregnant sows.
In secondary hosts, the disease presents with intense itching (pruritus) at the site of infection, severe enough to cause self-mutilation. Neurological signs are prominent in these animals, often resembling rabies, and can include abnormal gait, tremors, convulsions, and excessive salivation. The disease progresses rapidly and is usually fatal within days of symptom onset.
Human Health Considerations
Pseudorabies Virus is not known to infect humans, with no documented cases of human infection with classical PRV strains. However, some recent reports from China suggest a possible association between variant PRV strains and human encephalitis or ocular disease. These findings are based primarily on viral genetic material detection and require further confirmation.
The virus does not pose a direct threat to human health through contact with infected animals or consumption of pork. Meat from inspected pigs is considered safe for human consumption. PRV management focuses on animal health and preventing economic losses in livestock industries.
Prevention and Management
Prevention and control of PRV involve vaccination, which plays a significant role in swine populations. Modified-live and killed vaccines are available, aiming to reduce disease incidence and severity, and limit virus shedding. These vaccines often include gene deletions, allowing differentiation between vaccinated animals and those naturally infected through companion diagnostic tests.
Strict biosecurity measures are essential to preventing PRV introduction and spread within herds. This includes hygiene practices like cleaning and disinfection of facilities, and controlled animal movement. Quarantining new animals before integrating them into existing herds is also standard practice. Effective pest control, particularly targeting rodents and other wildlife that could carry the virus, helps minimize transmission risks.
Diagnostic methods, such as polymerase chain reaction (PCR) and serology, are used for surveillance and to confirm PRV infections. PCR tests detect viral genetic material, while serological tests identify antibodies, indicating exposure. These tools are important for monitoring herd health and implementing timely control measures. The United States, for example, successfully eradicated PRV from its commercial swine herds by 2004 through comprehensive control programs, though the virus can still be found in feral swine populations.