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inactivated by the sun's rays, thus explaining a fewer occurrences of foot and south disease in animals during these periods of the year, as compared to the autumn and winter months.
SOURCES OF INFECTION AND MEANS OF PROPAGATION.
The main sources of the disease are sick animals and those that have recovered from an attack of the foot-and-mouth virus, as well as, the products and raw materials obtained from such animals, and the contaminated media of their environment (such as barns, farm lands, pasture grounds, water, etc.). The carriers of foot-and-mouth infection can be humans, transport, infected house pets, wild animals and birds, which have visited a foot-andmouth disease center.
while studying the epizootic flare-ups of foot-and-mouth disease in fresh farms and settlements, which had no previous record of such epizootic areas at great distances from disease centers (sometimes as much as hundreds of kilometers), we did not find even one case where an animal affected by the foot-andmouth disease, had passed-on the disease directly. In the greater number of cases (70%), the infection was transported by humans, who were present in the foot-and-mouth disease center and assumed the role of carriers of the virus to far away regions. Thus, the foot-and-mouth virus was introduced into the VINITSKAYA region from the foot-and-mouth center in Rastov, Kiev region, and from the Sums'kaya region such an infection was carried to the Zhitomirs'kij regions. in most cases in fact it was because timely measures had not been undertaken in the foot-and-mouth center, namely, veterinary, hygiene check posts had not been set upto carry out the required checking of persons who had been present in the region of the foot-and-mouth center, formalin-steem chambers had not been set up to disinfect peronnel [personnel] and upper clothing, special uniforms, shoes, etc. The second reason for the spread of the foot~and-wouth infection (14%) was, according to our data, transport vehicles, mainly of the autocar types, which were not checked by veterinary check posts, because of non-availability of such check posts at the time, these vehicles were not aiways properly disinfected while leaving the farms where the foot-andmouth center, was located.
Very often (in 4% of the cases) the foot-and-mouth infection was caused by milk products which were not properly treated at the dairies and were products of animals which developed footand-mouth disease later. This milk wae used to feed the calves and young pigs in farms which had remained unaffected by the virus. The infected milk and other milk products were specially harmful because the very young calves and young pigs generally had very low resistance to the foot-and-mouth virus, which in such cases, occur in a non-aphthous (septic) condition, resulting in a large number of deaths among the young ones. That is usually the reason
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why a correct diagnosis of the foot and mouth disease has often been delayed in newly born calves and pigs, consequently, the farms cannot commence to take the necessary timely measures to combat foot and mouth infection, thereby allowing the virus, time to attack full grown animals,
The spread of foot and mouth disease through milk products, is characterized by the fact that the infection has usually been transmitted to farms where a particular milk dairy is operating. In fresh out-breaks of foot and mouth disease, in farms, where the infection has been transmitted through milk products, as a rule, the infection first starts attacking calves and piglets. In the transmission of foot and mouth infection through milk products, even one farm which has been attacked by the foot and mouth disease, is sufficient to spread the disease to others as yet unaffected, because of a dairy which had not carried out the necessary purification of the milk.
As far as the role of products of animal farms themselves, in the spread of foot and mouth infections, we have not established a single case where the virus was transmitted to such distant regions.
Very often, foot and mouth virus is transmitted to farms, which have not so far been affected by the disease, through water, specially rivers. Thus, during a foot and mouth epizootic in many farms of the Republic, fresh outbreaks in farms which have not so far been affected by the virus were observed by veterinary specialists in regions which were connected by river waters. The data collected by our Scientists indicated four cases, where the epizootic foot and mouth flare-ups had occurred in farms which were situated down stream at distances of 6 to 18 km, from the source of the foot and mouth infection and where the cattle continued to be watered untill such time as the foot and wouth disease became evident in these animals.
Excrita and Urine play a very important role in the spread of foot and mouth infection. According to our data, 4% of foot and mouth infections has resulted from excreta and urine of diseased cattle. It has been established that during the cold weather, the foot and mouth virus remains virulent in the excreta for a period of 150 to 168 days, hence the excreta and urine should be considered as very important agents in keeping the infection alive in outer media. If it is taken into consideration that during the winter months, it is practically impossible to render harmless the excreta of cattle suffering from foot and mouth disease or to completely disinfect the grazing lands of the animal farm in the grip of foot and mouth disease, then the importance of the excreta and urine in the propagation of the disease acquires even more significance.
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Sometimes, during the foot and mouth epizootic in the Ukraine, the unaffected farms, situated at long distances from the affected regions, were known to have been attacked by the virus as a result of transmission of the infection through forage ( hay, green fodder, etc.).
A definitely active role was played in transmission of the virus from regions infected by foot and mouth disease to unaffected farms by animals which were immune to this infection ( namely cats and dogs ) as well as, wild birds. A case has been known where foot and mouth infection was introduced into a farm, so far free from the infection, by rocks during the winter period. This has been proved by the fact that a very heavy snow fall in this particular farm area had completely cut it off from the surrounding inhabited regions, in other words, the only possible source of the foot and mouth infection was the rocks.
Literature has given a lot of information which proves that the Artiodactyla plays an important role in the propagation of foot and mouth disease.
In one of the farms of the Sumskaya regions, V. P. Litvin ( 1968 ) observed a case where foot and mouth infection was transmitted through a sick moose, which before the infection was discovered, grazing for some time with a group of young cattle in a pasture, S. I. Dzhupin ( 1965 ) also mentions the importance of wild Artiodactyla in transmitting the foot and mouth infection in the Novosibirsk regions.
The protracted virulence of foot and mouth virus and the active virus carried animals who had been affected by the disease, is a very important factor in the spread of the infection. Thus, according to the data of O. L. Skomorokhov ( 1952 ), a foot and mouth virus was observed in the urine of an animal 146 days after it was proclaimed clinically free of the disease. S. I. Dzhupin ( 1965 ) informs us that animals which had developed the foot and mouth disease were carriers for a period of 3 to 12 months after they were considered clinically healthy.
In our estimations, 7% of the foot and mouth epizootic cases were caused by animal virus carriers. The extended period of infection, due to the foot and mouth infection in some farms of the Khmel'nic'kaya region may be explained by the fact that stock which had suffered from the disease was mixed with groups of mature cattle which had not been affected so far. It has been established that the animals which had recovered from the foot and mouth disease remained carriers of the virus for a period of 17 to 18 months. Thus, the cause of the foot and mouth disease in 1967 among the animals of the Derazhnyanskaya department of the "Zagotskotvidgodivlya" ("State purchasers of animal food") (Vinnichnij region), were pigs brought in for fattening from the
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