Rabies

Rabies

R SWANEPOEL
Rinderpest

Introduction

Rabies (rabidus, L. = mad) is a highly fatal disease of humans and all other warm-blooded vertebrates, caused by a virus which is present in saliva late in infection and which is generally transmitted by the bite of diseased animals, most commonly dogs and other carnivores. Virus introduced into the bite wound enters peripheral nerves and, during an incubation period of weeks to months, spreads to the spinal cord and brain to produce severe nervous disease that lasts from a few days to weeks. The disease is usually marked by excitability, furious behaviour, inability to swallow, salivation, convulsions, paralysis, coma and death. Human patients often exhibit fear of water and this has given rise to the alternative name of hydrophobia for the disease in humans.

The disease appears to have occurred widely in Europe, Asia and Africa throughout recorded history, but it never had the significant impact on human and livestock populations classically associated with diseases such as bubonic plague, smallpox, bovine pleuropneumonia or rinderpest. Nevertheless, the dramatic nature of the signs and symptoms and the invariably fatal outcome of infection has long caught the imagination, and recognizable descriptions of the disease can be traced back further in early Chinese, Egyptian, Greek and Roman records than descriptions of any other infectious disease.765 Controversy raged for centuries as to whether the disease arose spontaneously, or was caused by an agent transmitted by bite, and it was not until 1804 that Zinke784 published a description of the experimental transmission of the disease to dogs and cats by brushing saliva from a rabid dog into wounds. In 1879, Galtier276 described the transmission of the disease to a laboratory host, the rabbit, and thereby paved the way for the historic work of Pasteur and his associates.

Pasteur soon established the essential association of the causative agent of rabies with nerve tissue, and demonstrated by serial intracerebral passage of infected nerve tissue in laboratory animals that wild or ‘street virus’ could be transformed into ‘fixed virus’ with a shortened and reproducible incubation period.520

The concept of specific immunization against infectious diseases had recently been developed by Pasteur and his associates for fowl cholera and anthrax, and in logical extension of their work they reasoned that vaccine could be administered to humans after exposure to rabies virus in order to induce immunity before the infection became established in the victim. They 'attenuated’ rabies virus by desiccating strips of infected rabbit spinal cord over potassium hydroxide, and administered suspensions of increasing ‘virulence’ to patients, starting with material dried for 14 days and ending with material dried for two days. The technique was first applied in 1885 on a nine-year-old boy, who survived, and within a short period the technique found widespread application and had a lasting impact on rabies immunization practices.519 It can be deduced that Pasteur’s method of preparing vaccine did not constitute attenuation of virus in the modern sense of the term, but resulted in the initial administration of inactivated virus followed by increasing doses of live virus.

Despite the development of a vaccine, the true nature of the infectious agent remained obscure and it was not until 1903 that Remlinger554 demonstrated that it passed through filters which retained bacteria, and thus conformed to the newly defined group of agents known as viruses. In the same year, Negri492 described the occurrence of cytoplasmic inclusions in infected nerve cells, and while the discovery of these ‘Negri bodies’ facilitated the specific diagnosis of rabies, the author himself considered the inclusions to be protozoan parasites, hereby fuelling controversy about the aetiology of the disease which was to continue for many years.

Pasteur’s vaccine had the disadvantage that fresh batches had to be prepared constantly, and hence Fermi introduced a method in 1907 of preserving vaccine, while at the same time achieving partial inactivation of virus, through treating infected nerve tissue with phenol.251 The method was modified by Semple in 1911 to achieve more complete inactivation of virus.601 Semple-type vaccines prepared from infected nerve tissue from a variety of animals (particularly mouse brain) and inactivated with a variety of chemicals, especially formalin, remained in general use for humans and domestic animals for many decades, in some countries up to the present day, until superseded by inactivated or attenuated vaccines prepared from virus grown in chick embryos, duck embryos and cell cultures.

In parallel with the development of an understanding of the mode of transmission of rabies infection, the early literature reflects growing opinion that the disease could be controlled by restriction and muzzling, or quarantine, of dogs, plus the destruction of strays.765Elimination of rabies through the application of such measures was achieved in very few instances only, when the control of the disease was uniquely favoured by the insularity of the country concerned and by the lack of wild reservoirs of infection. Control was first achieved in the Scandinavian countries of Norway, Denmark and Sweden in 1826345 and in Britain in 1902 after the promulgation of Anti-rabies...

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