Canine distemper virus

Concern over emerging infectious diseases and a better understanding of their causes have resulted in increasing recognition of the linkages among human, animal, and ecosystem health. Historically, the connection between animal and human health was understood and accepted, with the term “One Medicine” appearing in English texts as long ago as the 19th century ( 1 , 2 ). However, during the early 20th century, human and veterinary medicine diverged into discrete fields with reduced overlap. At this time, infectious diseases afflicting humans and animals were rarely considered in the context of broader environmental issues ( 3 ).

In viral diseases of plants, such as tobacco mosaic disease, the natural host was readily available and appropriate. For human diseases, such as rabies and polio, nonhuman hosts were necessary to isolate and characterize the etiological agent. In the case of rabies, a zoonosis that spreads from animals to humans with catastrophic results, the development of animal models might be expected to be productive. In contrast, polio and human influenza were not known to have animal hosts, nor was an animal host known for yellow fever. Yet, isolation and study of the agents for each of these diseases were achieved in experimental hosts. This chapter discusses the transmission of rabies to dogs and rabbits and polio in monkeys, which served as animal models for study. Isolation in monkeys, and particularly in mice, was exceptionally productive for filterable viruses that caused epidemics of encephalitis. These viruses were transmitted by mosquitoes and came to be called arthropod-borne, later shortened to arbovirus. Rabies is horrific in all aspects: in the savage bites by crazed wolves or dogs to implant infection, in the anxiety and fear in anticipation of whether the disease will develop, in the torturing expression of the acute disease, and in the knowledge that once expressed, rabies is an essentially fatal disease. Studies on biological systems showed that the embryonated egg of chickens was remarkably productive for the understanding of human influenza infection.

This chapter focuses on recently emergent paramyxoviruses that are associated with zoonotic disease, Hendra virus (HeV), Nipah virus (NiV), and Menangle virus (MeV). Molecular biological studies have made substantial contributions to the characterization of recently emergent zoonotic paramyxoviruses. As for other paramyxoviruses, the NiV surface glycoproteins are the primary targets for neutralizing antibodies. The conservation of most of the structurally important amino acids suggests that the attachment proteins of HeV and NiV would have structures that are very similar to the structure proposed for the attachment proteins of other paramyxoviruses. The development or characterization of animal models to study henipavirus infections is critical for understanding their pathogenesis and for development of therapeutics or vaccines. The chapter describes the pathogenesis and immune responses of human infections for each virus. Traditional techniques of virus isolation in cell culture, electron microscopy, enzyme-linked immunosorbent assay-based serology, neutralization assays, and immunohistochemical (IHC) techniques have been employed in the diagnosis of the zoonotic paramyxoviruses. NiV and HeV are internationally classified as biosafety level or biosecurity level 4 (BSL-4) agents; thus, clinical specimens suspected to be infected with these agents must be handled with caution. Pig farmers in areas in which NiV may be endemic should be educated regarding the features of Nipah encephalitis in pigs and to report any unusual disease. Since transmission is possible without close contact with pigs, exposure to potentially infected animals should be completely avoided, if possible. Persons handling pigs or their excreta should wear protective equipment such as gloves and masks.

Domesticated mammals include dogs, cats, cattle, sheep, goats, pigs, horses, donkeys, and camels. Agents are acquired from domestic animals by contact, ingestion, inhalation, or inoculation. Some agents are host specific and do not readily cross species, in particular, some zoonotic viruses. Other agents have a broader host range, for instance, Lyssavirus, Brucella, Francisella, Salmonella, microsporidia, and Toxoplasma. In rare instances of species jumps from mammals to receptive humans, severe (virgin territory) epidemics can result. Examples include human immunodeficiency virus, Henipavirus, and severe acute respiratory syndrome-associated coronavirus. This chapter talks about the various types of infections spread by dogs, cats, domestic bovids, suids, equids, and camelids.

This chapter describes the outbreaks of disease caused by Megamyxovirus zoonotic agent; provides an updated description of the virus, its genome, and its wildlife reservoir; and documents what is known of the pathology and pathogenesis of equine morbillivirus (EMV) infection. A severe outbreak of respiratory disease occurred in the second half of September 1994 in horses stabled in the Brisbane suburb of Hendra. The outcome of the outbreak was that 13 horses died. The trainer died after hospitalization with severe respiratory involvement, while the stable hand recovered after a protracted illness. Although horses had been moved off the property during this period, infection had not spread to distant sites and extensive surveillance showed that the virus was not active in horses or humans. In fluorescent-antibody tests, sera from naturally infected horses and humans reacted strongly with the fruit bat virus. Identical viruses were isolated from a range of tissues from horses infected during the initial outbreak and from a kidney of the deceased trainer. Morphologically the virus is a member of the family Paramyxoviridae. The pathology of field and experimental EMV infections in horses and experimental infections in cats has been described. It is sufficiently different from known members of the Paramyxoviridae to be considered a member of a new genus which bridges the two existing genera Paramyxovirus and Morbillivirus. The author proposes that consideration should be given to creating a new genus within the family Paramyxoviridae, subfamily Paramyxovirinae, to be called Megamyxovirus, with the type species being EMV.