TICK BORNE ENCEPHALITIS IN EUROPE/SOME ASPECTS OF EPIDEMIOLOGY AND CONTROL/DIONYZ BLASKOVIC

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80T00246A011900140001-4
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 29
• Document Creation Date: December 22, 2016
• Document Release Date: December 3, 2010
• Sequence Number: 1
• Publication Date: December 14, 1960
• Content Type: REPORT

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Tick-b or MilEi4't?dOk" 'I ttgLi$+'Igairope
Some aspects of epidemiology and control
Dinnyz Bla?`kovi(:
Institute of Virology, Czechoslovak Academy of Sciences, Bratislava
Tick-borne encephalitis is a virus infection of man and ani-
mals usually affecting their central nervous system. The disease
develops following a tick bite or after drinking infected goat's
and probably also cow's or sheep's milk. The domestic animals be-
come infected by ticks harboring the encephalitis virus.
(tayga)
Various infections such as Russian spring-summer encephalitis
(Zilber, 1939), bi-phasic meningoencephalitis (Smorodintsev et al.,
1954), Central European encephalitis (Gallia et al., 1949) and
louping-ill are classed under the term of tick-borne encephalitis.
Louping-ill is predominantly a disease of sheep. No special at-
tention has been paid to naturally occurring human Infections, the
clinical course of which has been studied mostly on laboratory in-
fections. Other encephalitides have a different clinical course,
varying from mild benign forms (the majority of Central European
encephalitides and bi-phasic meningoenoephalitides of Bielorussia
and Ukraine) to the very severe ones ending in paralyses of dif-
ferent muscle groups, destruction of nerve centres and sometimes
in death, as is the case with Russian spring-summer encephalitis.
This occurs in the eastern parts of European Russia (Ural) and
prevails in Siberia and the Far East.
Ticks of the Ixodidae family act as both vectors and reser-
voirs of the virus.
Russian spring-summer encephalitis is transmitted by Ixodes
persulcatus ticks. Haemaphysalis ooncinna and Dermaoentor eilveam
ticks (Ryzhov and Skrynnik 1q 4'1 ; Skrynnik and Ryshov 1940
also participate in\maintenance and circulation of the vi
are of minor importance. Ixodep rSioinus acts as vector and
_ II TI c ~+ 1 77
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2
encephalitis as well as of louping-ill viruses.
The antigenic properties of the viruses recovered from diseas-
ed or apparently healthy host animals and human oases are very milar. The viruses under consideration belong to the B si
arbor viruses (Casale and Brown 1 group o of
954). The louping-ill, bi phasic
meningoenoephalitis it and Russian spring-summer encephalitis vi-
ruses can be distinguished from one another either by the antibody
absorption and agar gel preoipkin technic (Clarke, 1960) or by
the pathogenicity for Maoaoa rhesus monkeys (Ilyenko and Pokr
1960). The viruses of Central ovskay8
European 8ncephalitis and bi-phasic
meningoenecephalitis have been shown to.be antigenically identica
(Clarke 1 1
960). The geographical distribution of the infections
of man and animals occurring in natural foci of infection is as
follows: northern parts of Great Britain (loupi ?
ng-111 ), the Euro-
pean part of the Soviet Union (both Russian spring-summer enoe ha-
litis and bi-phasic meningoencephalitis); and Austria p
Czechoslovakia, Finnland, German Democratic Republics Bulgaria,
Poland, Hungary,
Rumania, Sweden and Yugoslavia (Central European encepha-
litisy..
Fig. 1.
Viruses with a similar antigenic structure were discovered i
the Eastern Hemisphere n
Rzapaxat Siberia (Omsk hemorrhagic fever), India ggasan outside Europe in
( ur forest disease)
and Malaya (Tp 21, Langat virus). Quite recently,a new virus anti-
genioally closely related to the viruses of the tiok-borne enoe ha..
litis >~ Mc.Lean and, Donohvelgsq~~salcW6OTiem s.t*i. 60~.
group was disoovere n Canada po aeean v r e
tc~a+t The
(I A
used by
thes
e viruses are of world wide importance.
P
al
1. Ecology of the tiok-borne enoephalitis viruses
Tiok-borne encephalitis belongs to diseases occurring in na-
tural toes of infection. Pav3.ovsky (1939, 1956) defi .*
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focus of an infectious disease "as a tract of country of a defi-
nite geographical type containing habitats) in which certain
Geographically well-defined area characterized by the pre-
sence of a particular flora and fauna.
given interspecific relationships have evolved between the patho-
gen (the microorganism) and the vector or vectors. The latter
transmit the infective agent from animal donor to animal recipient
under conditions of the external environment conducive to, or pre-
venting circulation of the microorganism among the participants
of such biocenosesn.
This definition is very useful for understanding the natural
history not only of tick-borne encephalitis but also of other in-
fections such as tularemia, leptospirosis, babeniosis, yellows
fever etc., which are called transmissible diseases in the Russian
and arthropod-borne infections in the Arnerica^ English literature.
Man actually does not play a role in the circulation of tick-
-borne encephalitis virus in nature, he being the dead link in
the chain of infection.
Virus circulation in nature is effectuated by different in-
stars of Ixodes persulcatus, Dermacentor silvarum and Haemaphy-
salis concinna ticks in the tayga and forests of the Asian part
of the U.S.S.R. and in woods of the Ural, and by Ixodes ricinus
ticks in Western Russia and the rest of Europe. We will deal with
the ecology of the virus in respect to Ixodes ricinus. The geogra-
phical distribution of the main vectors and reservoirs of virus
is evident from Figure 2.
Fig. 2.
The circulation of the virus in nature is illustrated schema-
tically in Figure 3.'
Fig. 3.
Ixodes ricinus ticks are suckinrr the hlnnA an ia,wal 4"stars
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mainly on small rodents anlInS ctivorous animals, birds and
reptiles. Occasionally they feed on bigger and big beasts of
chase (deer, roebuck, fox, hare), domestic animals (cow, sheep,
goat) and man. The nymphal instars are feeding on all the animal
species mentioned and man, but especially on domestic animals
grazing in areas infested by ticks. Adult ticks are found almost
exclusively on big wild and grazing domestic animals and man.
Both wild and domestic animals do not succumb after .n.-Feotii
bqr} a bite by a virus carrying tick. There are neither deaths nor
mtt&- signs of disease, except of a slight temperature increase, in
domestic animals inoculated subcutaneously with large amounts of
virus (0.04 ml. per kg. body-weight of a 101. suspension containing
~QSSa,a-)
10 mouse LD50 per 0.03 ml.) (Gre~ikovA, 1957 a,b,cy. Nonimmune
domestic animals ,goats, sheep) grazing for one season in a natu-
ral focus of tick-borne encephalitis produce only specific antibo-
dies without a clinical manifestation of disease (5koda and Bla-
kovi?t 1958). Specific complement-fixing, haemagglutination inhibit-
ing as well as virus neutralizing antibodies develop quite regular-
ly in animals infected naturally with the virus. The demonstration
of antibodies serves as a basis for conclusions about the presence
of virus in nature.
The infectious process caused by virus transmitted to a host
animal depends on the state of susceptibility or immunity of the
animal (Benda 1958).
In animals which ks acquired immunity following a previous in-
fection, feeding of infectious ticks will not cause viremia, whe-
reas viremia of varying duration will develop in non-
immune animals. The viremic phase lasts 4-6 days in roes and hares,
on the average 5 days in laboratory mice (Libikova and Albrecht
1958), and 6, 5 and 4 days respectively in goats, sheep and cows
lasea~, e-)
(Grelkovd, 1957 a,b,ct-:-~The affected animals in the viremio stage
serve as source of infertio i fo' noninfectioug? 13oks. Because ?i-
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rus remains infective in"
rged f`oi~. Aevera,l consecutive
instars and may even be transmitted transovarially, the persis-
tence of the virus in a natural focus of infections is secured
provided that there is a sufficient supply of hosts. Virus spread
is secured into the next surroundings by the ticks themselves and
host animals includrn*
into distant areas by means ofYmigrating birds. The duration of
viremia and the level of virus content in the blood are of deci-
sive importance for the preservation of virus in nature (vn-
Smith, 1954).
Following the viremic stage, during which the virus can be
isolated from wild animals in nature (Przesmycki et al., 1960),
the virus becomes fixed in tissues, predominantly in the brain,
where it can be easily demonstrated. Following experimental sub-
cutaneous infection with 100-1,000 mouse LD50 of virus of Micro-
mys minutus mice caught in the field it was possible to demonstrate
the virus in them after 31 days (Mornsteinovi and Albrecht, 1957).
It is not known whether animals preserving the virus in brain tis-
sue can serve as source of infection for ticks by developing seoon-
dary viremia. The'presence of circulating antibodies seems to of-
fer evidence against such a possibility. Alimentary infection of
m
predators after consuption of such animals cannot be excluded, how-
ever. So far, no satisfactory evidence of this has been offered.
The state of immunity of host animals, both wild and domestic,
can be one of the regulators of the amount of virus present in
ticks and of the total amount of virus present in a natural focus
of infection. We mentioned already that immune animals do not de-
velop viremia even if infested with infectious ticks. On the con-
trary, the virus doses from the ticks act as revaccination doses
leading to increased titres of antibodies.
On the other hand, antibodies affect the virus present in tioks.
Extensive experiments (Benda 1958$) showed that blood from an immune
animal can > - show no ffeat on the_ virus titer in infeotiow
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ticks following engorgemen , or can cause a decrease in the titer.
There is a decrease in the tiler of virus transmitted to the next
instar of such ticks as compared with the controls. When nymphs
are sucking blood from an immune animal, further transstadial trans-
mission of virus is irregular or does not take place. Sucking of
immune blood does not free the tick from virus, it causes a decrease
in the titer of virus or an irregular transmission of virus to
the subsequent instars.
The tick-borne encephalitis virus is transmitted transstadiall?
in ticks. This fact has been known since the first investigations
on tick-borne encephalitis and has been demonstrated su 8essfully
br most investigators in different species of ticks: Ixodes per-
suJc tus ~Chumakov, 1944), Dermacentor silvarum (Ryzhov and Skryn-
Tai: