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Dispatches
Rat-to-Human Transmission
of Cowpox Infection
Tom F.W. Wolfs,* Jaap A. Wagenaar,† Hubert G.M. Niesters,‡
and Albert D.M.E. Osterhaus‡
*Wilhelmina Children’s Hospital/University Medical Center, Utrecht,
the Netherlands; †Utrecht University, Utrecht, the Netherlands; and
‡University Hospital, Rotterdam, the Netherlands
Suggested citation for this article: Wolfs TFW,
Wagenaar JA, Neisters HGM, Osterhaus ADME. Rat-to-human transmission
of cowpox infection. Emerg Infect Dis [serial online] 2002 Dec [date
cited];8. Available from: URL: http://www.cdc.gov/ncidod/EID/vol8no12/02-0089.htm
We isolated Cowpox
virus (CPXV) from the ulcerative eyelid lesions of a 14-year-old
girl, who had cared for a clinically ill wild rat that later died. CPXV
isolated from the rat (Rattus norvegicus) showed complete homology
with the girl’s virus. Our case is the first proven rat-to-human
transmission of cowpox.
A 14-year-old girl was admitted to the hospital with ulcerated nodules
on her upper lip and her left lower eyelid and several molluscum-like-lesions
on her right eyelids (Figure 1). She was feverish
but otherwise in good health. Values of complete blood and differential
counts were within normal limits. The erythrocyte sedimentation rate was
41 mm the first hour, and she was treated orally with ciprofloxacin. Within
a few days the lesions on her eyelids developed into crater-like ulcers,
which were surrounded by inflammatory tissue and were later covered by
thick black crusts; and sedema and erythema developed on the right side
of her face. At home she kept turtles, hamsters, guinea pigs, birds, ducks,
cats, and a dog. She also cared for a clinically ill wild rat, which she
had found 2 weeks before admission. After 6 days of care, the rat died
and was buried. During the following 4 weeks, the ulcerated lesions on
the girl’s face healed and left atrophic scars.
Routine virus isolation procedures from biopsies of the eyelid lesions
in Vero cells showed the presence of Orthopoxvirus. Serum immunoglobulin
(Ig) M antibodies to the viral isolate and to Vaccinia virus were
detected upon admission. The virus was identified as Cowpox virus
(CPXV) by polymerase chain reaction (PCR) and sequence analysis (PCR directed
at the Orthopoxvirus fusion protein gene, as described by Chantrey
et al.) (1). The rat, identified as Rattus norvegicus,
was recovered for laboratory testing. CPXV was isolated from brain samples
from the rat, and a swab was taken from its paw. Sequence analysis of
the rat’s virus indicated complete homology with the girl’s
virus. As shown in Figure 2, the sequence analysis
clearly demonstrates that the virus was CPXV.
Human CPXV is a rare zoonosis, which is transmitted as a result of contact
with animals. Usually localized at the site of inoculation, CPXV lesions
progress from a papule through vesiculation and pustulation into an ulcerative
nodule, which is covered with an elevated border with a black eschar.
Ulcera heal with scar formation. Differential clinical diagnosis of CPXV
includes herpes virus infection, anthrax, and orf (caused by a Parapoxvirus).
CPXV is almost always a self-limiting disease in immunocompetent hosts.
Although wild rodents are the reservoir hosts of CPXV (1), transmission
to humans has only been described from accidental hosts such as infected
cats, cows, and animals in zoos and circuses (2-4). Circumstantial
evidence of rodents as source of infection has been reported in two human
cases: one infection was associated with a suspected rat bite (5);
the other infection was in a person who cared for a sick wild field mouse
(6). Person-to-person transmission has not been reported.
Our case is the first proven wild rodent-to-human transmission. Serologic
surveys have shown that CPXV is a widespread endemic infection in European
wild rodents with the highest seroprevalence in bank voles (Clethrionomys
glareolus), wood mice (Apodemus sylvaticus) and field voles
(Microtus agretis) (1). Seroprevalence rates in
rats are not available; therefore, whether rats might also be reservoir
hosts or act as liaison (accidental) hosts is unclear. Since smallpox
has not occurred naturally anywhere in the world since 1977, immunization
with Vaccinia virus has been discontinued, which has led
to a declined cohort immunity to orthopoxviruses including CPXV, and thus
may result in an increased incidence of human CPXV infections (2,7).
Physicians must be aware that zoonosis may not only be contracted from
accidental hosts (e.g., cats and cows) but also directly from a primary
natural reservoir (rodents).
Dr. Wolfs is an infectious diseases pediatrician at the Wilhelmina Children’s
Hospital, Utrecht, the Netherlands. His research interests include HIV
and the interaction between viral and bacterial infections.
References
- Chantrey J, Meyer H, Baxby D, Begon M, Bown KJ, Haxel
SM, et al. Cowpox:
reservoir hosts and geographic range. Epidemiol Infect 1999;122:455–60.
- Willemse A, Egberink HF. Transmission
of cowpox virus infection from domestic cat to man. Lancet 1985;1:1515.
- Vestey JP, Yirrel DL, Aldridge RD. Cowpox/catpox
infection. Br J Dermatol 1991;124:74–8.
- Baxby D, Bennett M, Getty B. Human
cowpox 1969–93: a review based on 54 cases. Br J Dermatol 1994;131:598–607.
- Postma BH, Diepersloot RJA, Niessen GJCM, Droog RP. Cowpox-virus-like
infection associated with rat bite. Lancet 1991;337:733–4.
- Lewis-Jones MS, Baxby D, Cefai C, Hart CA. Cowpox
can mimic anthrax. Br J Dermatol 1993;129:625–7.
- Vestey JP, Yirrel DL, Aldridge RD. Cowpox/catpox
infection. Br J Dermatol 1991;124:74–8.
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