Pox Diseases

acute infectious viral diseases of man and animals.

Man. In man, smallpox (Variola vera) is characterized by high contagiousness and a distinctive nodular-vesicular rash followed by scarring; the disease’s course is often very severe. References to smallpox are found in ancient Egyptian and Chinese manuscripts, in the works of ancient Greek and Roman physicians, and in 15th-century Russian manuscripts. The disease entered Europe from Asia in the 13th century during the Crusades and was brought from Europe to America on the ships of H. Cortés in the 16th century. Between the 15th and 18th centuries, smallpox epidemics in Europe killed hundreds of thousands of persons and disfigured the survivors’ faces. The practice of quarantine, begun in the 18th century, had little effect.

The turning point in the struggle against smallpox was the discovery of vaccination in 1796 by the English physician E. Jenner. However, it took a long time for this method to become widely used. In Russia, as late as the period between 1891 and 1912, approximately 100,000 persons contracted the disease yearly. After Lenin’s decree introducing compulsory vaccination in 1919, the incidence of the disease began to decline; by 1937 it was completely eradicated in the USSR. It is still high in many Asian, African, and Latin-American countries, where there occurred 50,000 to 90,000 cases yearly between 1950 and 1972; thus, smallpox may be brought into countries where it has been eradicated. For example, 24 cases were brought into the United States, Great Britain, France, Poland, and the USSR between 1947 and 1968. As a result of the disease’s spread, 258 persons in these countries (excluding the United States) became infected and 51 died. In 1958 the Soviet government proposed a worldwide program to eradicate smallpox that was adopted by the World Health Organization, and made available a large quantity of smallpox vaccine for this purpose.

The causative agent of smallpox is a filterable virus that is resistant to drying and to the effect of low temperature. (The virus is visible under a microscope after special treatment.) The source of the infection is a person with the disease. The virus is transmitted through the air together with dust or drops of mucus or, less commonly, by means of articles such as linens, clothing, and toys. The incubation period is between five and 17 days, with an average of 14 days. The disease begins with a sharp rise in temperature (to 40°C), severe headaches, nausea, and pain in the sacral area. At the end of the third day an eruption appears in the form of dull red spots on the face, extremities, body, palms, and soles. Subsequently, the lesions pass through several stages: papule, vesicle, pustule, and crust. The disease lasts from 35 to 45 days. Clinical variations of smallpox are confluent smallpox, a severe form in which the lesions merge; hemorrhagic smallpox (“black smallpox” or purpura variolosa), a very severe form with high lethality, in which hemorrhages into various tissues and organs occur; and varioloid, a mild form with low fever; in this form the lesions are isolated or do not pass through all the above stages. Smallpox may occur without a rash or fever; there are also other forms of the disease. Recovery imparts permanent immunity.

Antivariolic gamma globulin is used for the specific therapy of the disease. The principal preventive measure is vaccination. A quarantine disease, smallpox is controlled by international sanitary regulations and by sanitary regulations protecting each nation’s borders. A smallpox patient and those who have come in contact with him must be isolated and their homes and possessions disinfected. Persons who have been in contact with the patient must be revaccinated.

Animals. In animals, the agents causing pox in sheep, goats, monkeys, swine, rabbits, and some other animals are independent viruses. Susceptible to cowpox virus and the related variolovaccine virus are cows, swine, buffalo, camels, horses, asses, mules, elephants, rabbits, monkeys, and man.

The causative agents of avian pox occupy a special place. The virus of chicken pox is pathogenic for birds of the suborder Galli, while the viruses of pigeon pox and canary pox are pathogenic for birds of the Columbiformes and Passeriformes orders, respectively. Some strains of avian pox viruses can be doubly and triply pathogenic for birds of different orders, while at the same time immunizing them from the virus of another kind of avian pox. Mammals and birds contract pox more frequently and severely in winter and early spring, especially those which are young, those of domesticated breeds, and ornamental birds.

The sources of pox viruses are infected and recovered virus-bearing animals and humans. The course of the disease in animals is subacute and marked by intoxication, fever, and an eruption on the skin (exanthem) and on the mucous membranes (enanthem). The eruption passes through the distinctive stages of roseola, papule, vesicle, pustule, crust, and scar. Pox causes economic loss by lowering milk yield of cows and the laying capacity of hens. Animals suffering from pox lose weight and their skin becomes damaged; some of them die, especially when the disease is complicated by bronchopneumonia or gastroenteritis. Diagnosis is based on analysis of the clinical epizootological and epidemiological data, the pathoanatomical changes, and the results of laboratory tests. There is no effective specific therapy. Chemotherapeutic preparations are used to prevent and eliminate complications. Pox in animals is controlled principally by strict observance of quarantine and sanitary measures. Vaccines are used as a preventive measure.