VIRUS INFECTIONS OF "NORMAL" HEALTHY ANIMALS 
G. D. Hsiung and N. S. Swack* 
Longitudinal survey studies of virus infections in nor- 
mal healthy animals, including primates and non-pri- 
mates, showed that both groups may harbor latent vi- 
ruses. The greatest number and variety of viruses were 
recovered from tissues of rhesus and green monkeys. A 
herpesvirus was consistently isolated from inbred strain 
2 guinea pigs but only occasionally from the Hartley 
strain. Rabbits, hamsters and cattle were commonly free 
of virus infections in their kidney tissues. Two of ten 
lots of horse kidney cultures examined showed a herpes- 
virus infection. Circulation of simian viruses in mon- 
keys during captivity was observed to have occurred. 
Green monkeys acquire SV40 and foamy virus type 1 
from rhesus; whereas the latter acquire cytomegalo- 
virus from the green monkeys. Both monkey species may 
acquire SV5 infection from man. 
INTRODUCTION 
Previous studies by a number of investiga- 
tors have demonstrated the presence of a vari- 
ety of latent viruses in simian tissues.^-^ The 
recognition of these viral agents in primate 
tissues has proven to be important especially 
when the tissue cells are used for the prepara- 
tion of virus vaccines, or when the animals are 
used for medical research. A number of the 
viruses isolated from "normal" monkeys were 
shov^Ti to be oncogenic. These included: (1) 
SV40, a papova virus, isolated from apparently 
healthy rhesus monkeys,^" (2) several types of 
simian adenoviruses isolated from healthy 
African green monkeys, as well as from macaca 
monkeys," and (3) herpesviruses isolated from 
normal squirrel and owl monkeys.12.13 
During the past several years, we have con- 
ducted survey studies on the prevalence of virus 
infections in "normal" healthy animals, in- 
cluding monkeys, horses, cattle, rabbits, guinea 
pigs and hamsters. The comprehensive results 
of these studies are included in this discussion. 
• Department of Laboratory Medicine, Yale University School of 
Medicine, New Haven, Connecticut, and Veterans Administration 
Hospital, West Haven, Connecticut. 
Virus Infections in Primates and Non-Primates 
Primary cell cultures prepared from primate 
and non-primate kidney tissues were examined 
for the presence of latent viruses (Table I). 
Cultures in the primate group were prepared 
from the kidney tissues of rhesus and green 
monkeys; and in the non-primate group from 
the kidneys of guinea pigs, rabbits, hamsters, 
cattle and horses. It was noted that the pri- 
mate cultures, especially rhesus monkeys, 
showed a higher percentage of viral agents than 
the non-primate group. Of the 124 rhesus mon- 
keys, 65 viruses were isolated; and of the 108 
green monkeys studied, 35 showed the presence 
of viral agents in their kidney tissues. 
A herpes-like virus was repeatedly isolated 
from inbred strain 2 guinea pigs and on two 
occasions was also isolated from Hartley 
guinea pigs.^* Since the virus persisted for the 
lifetime of the infected animals and transplacen- 
tal transmission of the virus in guinea pigs was 
demonstrated, it is speculated that most likely 
all strain 2 guinea pigs harbor the virus.^^ No 
virus was isolated from the kidney cell cultures 
prepared from 211 New Zealand white rabbits, 
Table I. — Latent Virus Infections in Primary Cell Cul- 
tures Derived from "Normal" Healthy Animals 
August 1969— 
-June 1971 
Animals 
Studied 
No. 
Studied 
No. 
showed 
latent 
virus 
%of 
virus 
infection 
Primates 
Rhesus Monkeys 
124 
65 
62 
African Green Monkeys 
108 
35 
32 
Non-Primates 
Guinea Pigs — Strain 2 (inbred) — 
82 
72 
88 
Hartley Strain 
198 
2 
1 
Rabbits — New Zealand White 
211 
0 
0 
Hamsters — Syrain Golden 
16 
0 
0 
Cattle 
50 
0 
0 
Horses 
10* 
2 
20 
* Nine horses were examined during January-May 1966.' 
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