NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
RESEARCH WORK ON FOOT-AND-MOUTH
DISEASE
207
that a given species is not susceptible, or if attacked is not infective for another
species.
(iii) Different types of virus. Besides difference in virulence and adaptation
of various strains of foot-and-mouth virus there are distinct " types " of virus
which have to be reckoned with. It was mentioned in the Third Progress Report
that Vallee had described two types of foot-and-mouth disease virus which he
called the O and A types, the former being much the commoner, and that later
Waldmann and Trautwein (1926) described a third type C. Waldmann originally
called his three types A, B and C since he did not know to which of Vallee's types
his strains corresponded. It is now generally agreed to retain Vallee's notation
for O and A and to use C for Waldmann's new type. The three types all produce
cases of disease and epizootics which are nearly or quite indistinguishable clini-
cally, but an attack due to one type does not protect animal's against the others.
Trautwein (1927) was able to infect with two of the types in succession 100 per
cent. of guinea-pigs, 84 per cent. of swine and 58 per cent. of cattle, and with the
three types in. succession 100 per cent. of guinea-pigs, 72 per cent. of swine and
37 per cent. of cattle. It appears that in cattle and pigs at any rate there is some
overlapping or extension of the resistance produced by one of the types to infection
with the other types.
Almost the only way of discovering the type to which a newly acquired strain
belongs is by inoculating with it animals immune to known types of virus in order
to see whether they are susceptible to the new strain.
Identification of types is important, because only by this means can it be
known whether recovered animals are liable to reinfection from another source
of infection, and also as an aid to tracing the origin of an outbreak. Only a few
strains have been found so far which cannot be placed into one of the three groups,
O, A and C, though in Waldmann and Trautwein's original paper (1927) some
slightly divergent variants were described.
Professor Ciuca examined four strains of foot-and-mouth virus at the Lister
Institute in 1927 from Roumania, and found that while one of these appeared to
be identical with the typical GF strain of O virus then in use, the other three
strains only showed incomplete agreement with the GF strain and the first
Roumanian strain but were certainly not of either the A or the C types.
Dr. Andrews, in the past two years, has determined the type of virus of 23
strains from different outbreaks in Great Britain, and 21 of these belonged defi-
nitely to the O type ; none corresponded to the A or the C type. The remaining
two strains were not like each other, nor could they be assigned to O, A or C.
Including those strains of virus previously recorded by Sir Stewart Stockman, 40
208 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, II
strains have now been examined from outbreaks in this Country. Of these 37 or
92 per cent. conformed to the O types, one to type A, and two belonged apparently
to hitherto undescribed types.
The type to which each of these strains belonged was first examined by means
of guinea-pigs and on the whole this seems to be the most satisfactory procedure,
since these animals react more regularly than cattle and it is very much easier
to inoculate as many as are required and also to keep in stock guinea-pigs immune
to the different types so as to be ready for testing new unknown strains. The
only difficulty in using guinea-pigs for this purpose is that it is necessary to make
sure that the fresh strain from a bovine is adapted and will readily infect the
guinea-pig. Of the 23 strains tested by Dr. Andrews, 20 which had been
diagnosed by the use of guinea-pigs as type O were subsequently tested on cattle
and the diagnosis of type O was confirmed. Dr. Andrews has also examined
10 strains of virus sent from the Argentine in September, 1928, through the
kindness of Dr. Fernandez Beyro of the Ministry of Agriculture at Buenos
Ayres. When tested on cattle three of them appeared to belong to the type O,
though by tests on guinea-pigs the result was not quite so clearly defined,
probably because of incomplete adaptation. Seven of the Argentine appeared
to be neither O, A nor C, since they caused foot-and-mouth disease in
animals which had recovered from attacks of each of these types. A similar
occurrence of apparently new types had been observed in the case of the
peculiar strains found in Great Britain and mentioned above, but it is not
known whether any of the seven Argentine non-conforming strains are of the
same type as either of the two unusual strains from this country. It has been
claimed by Modrow (1929) that virus type O differs from type A very considerably
in the size of the particles of which it is composed. This conclusion was the
result of experiments showing that O virus would pass through a collodion filter
with very much smaller pores than were required to allow A or C to pass. The
result of her experiments and the conclusions are very remarkable, since such a
difference between the types would be of great interest if they were confirmed,
especially if it could be shown that the difference was really due to the type of
virus used and not merely a peculiarity of the particular strain tested.
There have been occasional statements such as that of Manninger (1930) that
a strain of one type has changed its character and become assimilated to another
type. Such observations are very rare and must at present be accepted with
reserve.
N.—THE INFECTIVITY OF LIVING ANIMALS.
It has been shown by previous workers that in susceptible animals the con-
centration of the virus is greatest in the fluid contained in the vesicles when they
RESEARCH WORK ON FOOT-AND-MOUTH DISEASE
209
first appear and in the epithelial tissues of the vesicles. In guinea-pigs this is
especially the case in the primary vesicles at the site of inoculation on the feet.
The content of virus in the internal organs and the blood has been shown to be
much less.
Farm animals. It has long been recognised that animals may be infective in
the very early stages of the disease before the symptoms are very obvious.
Dr. Andrews made a detailed study of cattle infected by intramuscular inoculation or
naturally by contact with inoculated animals. He found that the blood was not
always infective at the same stage of the disease, and often not before vesicles had
appeared. The earliest stage at which the disease was communicated to others by
contact in these experiments, with one exception, was after vesicles had appeared
in the mouth and not as early as the first rise of temperature. The same was true
of cases in which the disease had been acquired by contact instead of inoculation.
Previous workers have stated that the urine and milk of cattle are infective
about the same time that virus can be detected in the blood, i.e., during the erup-
tion of vesicles and for two or three days later.
At Pirbright the milk has been found to be infective, and virus has also been
detected some times in the urine, but not with any regularity.
O.—SOURCES OF INFECTION.
Evidence adduced from the long experience on the reappearance of foot-and-
mouth disease after slaughter and disinfection in England has recently been sum-
marised by Sir Ralph Jackson. Out of 5,554 infected centres, which have occurred
in the course of the last 20 years where restocking has taken place from 4 to 18
weeks after the disinfection, in 57 the disease has reappeared, though in 13 of these
the disease was probably reintroduced.
Magnusson (1930) points out that material taken experimentally from animals
at the height of the disease retains infectivity as a rule much longer than the flakes
of epithelium, etc., thrown off naturally by the animal during recovery. The re-
covered animal also as a rule rapidly disinfects itself. He found that infection was
much more persistent in winter. Lebailly (1922) claimed that, 4 or 5 days after
the onset of the disease, cattle and the stalls in which they had been confined, as a
rule, ceased to be infective for fresh animals. This latter observation has been
confirmed at Pirbright at all seasons of the year under experimental conditions.
P.—THE DURATION OF INFECTIVITY.
It is generally accepted, especially as the result of a long series of observations
at Riems, that virus can only rarely be recovered from cattle as late as the 11th
day of the disease even when scrapings from the mouth and tongue are examined.
K
210 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, II
On the strength of these observations the isolation of cattle in Germany on an in-
fected farm was not continued beyond a fortnight from the recovery of the animals
infected by inoculation. It has, however, recently been found necessary to increase
the period to three weeks on account of the occasional later appearance of symp-
toms in animals which have been inoculated with virus and serum by the so-called
combined method.
It has, however, been believed that virus may be enclosed in the horn of the
hoof during recovery and then again be liberated after four months or more by
detrition or paring of the hoof. Though proof of this hypothesis has been sought
there is very little direct evidence in its favour. Brandt (1928), who investigated
103 cattle and 9 pigs from this point of view at Riems, believed that if virus was
retained it was present in dung or other dirt in fissures of the hoof and was not
really shut off from the reach of antiseptics applied externally.
In spite of the lack of evidence where virus may lie latent in a recovered
animal, Traum and Olitsky, at Strasbourg, found evidence of one animal retaining
infection and infecting another after 34 days among 23 cattle investigated, and
Brandt observed an infection of one experimental animal in the course of the exa-
mination of 103 cattle and 9 pigs in order to see whether any of them were carriers
36-67 days after they had been infected. Burgi (1928), in Switzerland, as the result
of prolonged field observations, maintained that recovered cattle retained infection
and started fresh outbreaks some months after they had recovered. Such a source
for an outbreak is scarcely likely to be operative in this country unless from a con-
cealed or overlooked case of disease. There is some reason to suppose that virus
might survive dried on the coat of an ox for some days if the animal were not tho-
roughly disinfected after recovery.
The ultimate source of infection in foot-and-mouth outbreaks has always been
considered to be cases of the disease in cattle, pigs and sheep and this is no doubt
correct in the main. It has, however, been shown of late years that other animals
are more or less liable to foot-and-mouth disease.
The susceptibility of the goat was investigated by Rippin (1929), who had no
difficulty in communicating the disease by inoculation, and in most animals with
which it was attempted three attacks with the three distinct types of virus were
given in succession. Some goats have also been artificially infected at Pirbright.
R.—FOOT-AND-MOUTH DISEASE IN OTHER ANIMALS BESIDES CATTLE, PIGS,
SHEEP AND GOATS.
Magnusson (1927) has recorded an epizootic among reindeer, and other rumin-
ants including camels may also suffer from the disease.
RESEARCH WORK ON FOOT-AND-MOUTH
DISEASE
211
It has been recongised in some countries, but it has been considered as a rule
unimportant, that the unexpected occurrence of foot-and-mouth disease in animals
other than ruminants and pigs might sometimes be the means by which infection
was spread. Such infections have been occasionally discovered or suspected in
several different species and this possibility has now and then been investigated by
laboratory experiments.
(i) Foot-and-Mouth Disease in Man. The susceptibility of man to foot-and-
mouth disease has seldom been conclusively proved, but two accidental infections
have occurred at Riems and been recorded by Pape (1921) and Trautwein (1930) in
which laboratory workers cut their hands with broken glass vessels containing virus
and suffered in consequence from a pronounced vesicular eruption, chiefly on the
injured part. In the latter case the nature of the disease was confirmed by animal
inoculation. A few other fairly well-substantiated cases are recorded, especially one
by Pancera (1921) at Como. Dr. Arkwright (1929) reviewed and published a sum-
mary of the chief recent evidence of this subject. Kling and Hojer (1926-1928)
suggested that the disease was spread in Sweden by men who were infected without
overt signs of disease and carried the virus in their throats. They obtained no
direct evidence in support of their hypothesis, and Waldmann and Trautwein (1928)
examined 40 men employed at Riems without finding any reason to endorse Kling's
views.
(ii) Rats. In the Second Progress Report, pp. 16 and 103, it is recorded that it
was found possible to infect wild rats by inoculation, but no increased adaptation
of the virus to the rat was obtained by passage of the virus through these
animals, nor did they infect one another when kept in the same cage. Since then
Beattie, Morcos and Peden (1928) at Liverpool, continuing the former work by
Beattie and Peden (1924), have succeeded in infecting wild rats by feeding them
with virus from guinea-pigs. This was mixed with crushed bones, in order to
increase the liability to inoculation by producing injuries to the mucous membrane
with spicules of bone.
Four rats, F. 1, 2, 3, and 4, with suspicious sores which were caught on a farm
in Yorkshire have been examined at Pirbright. Inoculation of material from one
of them, F. 3, resulted in the production in a guinea-pig of both generalised and
local vesicles which were with little doubt due to foot-and-mouth disease but the
attempt to pass the disease on to other guinea-pigs was unsuccessful. These four
rats were sent to Pirbright for examination because the Inspector of the Ministry in
charge of operations at a farm, the site of a foot-and-mouth disease outbreak,
noticed that the rats which were being destroyed there were lame and had abrasions
or ulcers on the feet. The rat from which the guinea-pig was infected had a small
vesicle on the tongue and abrasions on the toes.
K 2
212 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, II
On another occasion a rat, S. 1, was caught at the experimental station at
Pirbright, and from this animal foot-and-mouth virus was obtained. With this
virus guinea-pigs, wild and albino rate and swine have been infected and the virus
recovered from the infected animals has been passed through others in series. The
nature of the virus in this case was established beyond doubt by the character of
the vesicles in guinea-pigs and swine and by the subsequent immunity of the animals
infected. It was shown that the virus from S. 1 belonged to the type O. A stock
strain of O. virus from cattle and strain S. 1 both produced disease which gave
protection to animals when they were subsequently inoculated with either of these
two strains. Swine were infected by feeding them with the bodies of guinea-pigs
inoculated with the rat virus S. 1. Wild rats were infected by simultaneous inocu-
lation into the skin of the hind feet and into the muscles, and both local vesicles on
the feet and generalised vesicles in the mouth resulted. Rats were also infected by
feeding them with material from infected guinea-pigs mixed with crushed bone.
The signs of infection in rats consisted of vesicles on the feet and toes, on the ton-
gue and lips and on the tail. The diseased areas on the tail were mostly inconspi-
cuous and were indicated by small ulcers or crusts on any part of the tail. Virus
was obtained from lesions on the tail which were not very characteristic in appear-
ance. Altogether 132 rats caught at the experimental station at Pirbright and in
the immediate vicinity of the infected compound have been examined and six in all
have been found to be infected. Further experiments showed that not only virus
S. 1 from the wild rat but also another strain, Virus 1, which originally came from
a bovine in Great Britain, readily infected rats by inoculation. Three other strains
of virus from cattle were also communicated to rats, though less easily. These
three additional viruses were Virus 52, an O. type from cattle in England, a strain
sent from the Argentine, and the type A strain which originally came from Profes-
sor Vallée. Experimentally, the disease was found to spread from inoculated rats
to others which were kept in contact with them and from these contacts again to
others through association in the same cages.
Not only wild rats but also albino rats were infected by similar methods. It
was found that infection of rats could not readily be obtained unless they were
adults or at least half grown. This observation is comparable to the well-known
greater susceptibility of large guinea-pigs.
The difficulty in infecting rats in previous experiments as well as the failure to
pass the virus from one of the Yorkshire rats F3, to guinea-pigs in series was
probably largely due to the well-known obstacles to adapting some strains of virus
to a different species of animal from that to which it has been accustomed.
(iii) Rabbits.—It has been repeatedly shown that tame rabbits can be infected
with foot-and-mouth disease by inoculation and in the Third Progress Report,
RESEARCH WORK ON FOOT-AND-MOUTH DISEASE
213
pp. 71, 114, experiments with tame rabbits are recorded. It was found that the
disease occasionally spread from infected to healthy rabbits, probably as the result
of bites when they were kept at close quarters. In Appendix II to the present
Report, experiments are recorded by Mrs. Gibbs showing that wild rabbits can
also be given a mild infection by inoculation, but although healthy wild rabbits
were kept in a hutch with those showing vesicles, no spread of infection could be
observed. Further experiments with tame rabbits by Mr. Galloway are also
recorded.
(iv) Hedgehogs.—In the Second Progress Report, p. 51, Dr. Minett recorded
briefly that two adult hedgehogs were infected with foot-and-mouth virus by
inoculation, vesicles appearing on the inoculated feet from which virus was
recovered, and that both animals died within 15 days. A further study of the
disease in hedgehogs was begun by Mrs. Gibbs in 1928. In these animals, after
inoculation into the skin of the feet and into the muscles, vesicles appeared on all
four feet, and in the mouth and on the snout. The hedgehogs usually became
very ill, and were killed or died in a week or ten days. When healthy hedgehogs
were kept in contact with those which had just been inoculated they also showed
signs of infection 3 or 4 days after the onset of disease in the former. The disease
was also severe when the infection was thus acquired naturally by contact.
The virus recovered from hedgehogs was highly virulent since after grinding
up the vesicle epithelium in salt solution and filtering the resulting liquid was
infectious for guinea-pigs in dilution of one in a million.
These experiments have been continued by Dr. Edwards, who has used a large
number of hedgehogs. He found that they could only be infected with difficulty
when virus direct from guinea-pigs was used, but that when virus was recovered
from a hedgehog after inoculation and re-inoculated into an animal of the same
species the virulence for the hedgehog had risen rapidly, and that after passing
through two or three hedgehogs the adapted virus caused a very severe and fatal
disease, which spread rapidly by contact.
The hedgehog is the only species of animals besides farm animals in which rapid
spread by contagion of a severe form of the disease is known to occur, though
Dr. Andrews' experiments show that transmission by contact happens fairly often
in the rat in captivity.
When hedgehogs survive infection they are found to be insusceptible to further
inoculation and their blood is capable of neutralising the virus, like that of
recovered cattle, pigs and guinea-pigs.
In two experiments, hedgehogs did not catch the disease from infected guinea-
pigs with which they were kept in contact, but healthy guinea-pigs placed in the
214 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, II
same cage as infected hedgehogs did acquire the infection, which was believed to
enter through pricks made on the guinea-pigs' feet by the hedgehogs' quills.
Earlier experiments with other small animals have shown that rabbits, long-
tailed field mice, dogs, cats and hamsters can be infected in the laboratory, but the
disease has usually been mild and has not spread by contagion.
House mice and white mice have almost completely resisted attempts to infect
them.
(v) Cats.—Dr. Minett in the Second Progress Report described infection which
he had obtained in cats. The disease in adult cats appeared to be mild, but
young kittens when inoculated died without specific lesions.
Höve (1929) at Riems, has recently made a number of experiments with cats
and has shown that the disease, though not severe, could be passed from cat to
cat by inoculation and in one instance a healthy cat acquired infection by contact
with an inoculated animal. All the three types of virus, O, A and C were found
infective for cats.
Mr. Galloway has recently begun a study of the disease in cats. He met at
first serious difficulties due to distemper-like infections among the inoculated
animals. This was eliminated by breeding the stock of cats for experiments. He
has found that cats at 8 weeks old or more can be infected regularly by inoculation
and is pursuing the subject with a view to determining the ease with which they
can acquire the disease and the duration of infectivity and also how far they are
susceptible to strains of virus of different types and from different sources.
(vi) Dogs.—It is known that dogs can be infected in the laboratory, and some
experiments demonstrating this were recorded in the Second Progress Report :
no detailed study on this animal has been published of late years, till quite recently
(Trautwein, 1931).
S.—FOOT-AND-MOUTH DISEASE AND VACCINIA IN CALVES, ETC.
It was at one time suggested that vaccinia and foot-and-mouth disease conferr-
ed a certain degree of mutual protection against each other in animals, but this
has not been supported by recent work. Belin (1926-27) has claimed that inocula-
tion of suitable preparations of vaccinia and foot-and-mouth viruses together into
cattle results in an infection in which the foot-and-mouth symptoms are much
diminished in severity but immunity against the latter disease is secured. These
observations are not at present generally accepted and other workers have not
obtained confirmatory results.
The infection of calves and cattle with foot-and-mouth disease in the U. S. A.
(Mohler and Rosenau, 1909) by means of imported vaccine lymph used to produce