Research Results - (PDF, 101 mb) - USAID

Problem Statement and Approach
Ovine pulmonary carcinoma (OPC) and
lentivirus-induced interstitial pneumonia
produce severe economic losses in Peruvian
sheep. The natural coexistence of both
oncogenic type D and non-oncogenic retrovirus
(lentivirus) suggests a possible cofactorial role of
lentivirus in the development of lung tumors.
In an attempt to decrease losses in affected
Peruvian sheep farms, one of seven sheep
production units (mean = 25,000 head) at a large
sheep enterprise of the central sierra was selected
for research on retrovirus-induced
chronic pneurmonopathies. This production unit
has beer. isolated from the others for six years,
during which time no animal from any of the
others unit was allowed to enter the research
unit. Three of the ten flocks of ewe- (mean =
2,500) of this unit were selected as experimental
flocks and seven were left as controls. Ewes
sufferirg from chronic respiratory disorders
were eliminated periodically from the experimental
flocks, and annual serum tests were
conducted to determine the prevalence of OvLV
antibodies by the AGID test. The prevalence of
chronic pneumonopathies was determined by
gross examination at death by local veterinarians.
Justification
During the last eight years, extensive
field studies have been conducted in Peru,
particularly at the SAIS Tupac Amaru, to discover
the causes, improve the diagnosis, and
evaluate control strategies for chronic viral
respiratory diseases of adult sheep. In addition
to ovine pulmonary carcinoma (sheep pulmonary
adenomatosis), lentiviruses have been
found to contribute to respiratory disease and
have been implicated as a cause of a severe
indurative mastitis which limits milk production
in affected ewes. Serological tests and
histopathology have been used to determine the
prevalence and geographical distribution of
these diseases in Peru. This year the goal was to
complete baseline studies which will facilitate
future field testing of diagnostic tests and
vaccine products as they become available.
Project Progress
The occurrence of ovine pulmonary
carcinoma has been progressively decreasing in
the experimental flocks at the SAIS Tupac
Amaru. In 1985, the prevalence of pulmonary
carcinoma in the control flocks was 127/10,000
compared with 109/10,000 in the experimental
flocks. However, by 1989, the prevalence was
147/10,000 for the controls and only 48/10,000
in the experimental flocks. In order to compare
these results with the disease status of the entire
sheep operation (seven production units), the
prevalence of OPC during the last three years
was investigated in a second production unit.
The frequency of OPC in ewes of the latter unit
was found to be similar to the control flocks
during 1987-1989, with a prevalence of 114/
10,000 for 1989.
That the occurrence of the disease is
decreasing in the entire research unit and not
just among the experimental (ewes) flocks is
corroborated by the disease prevalence among
other classes of animals (adult and young). In
1989, the prevalence of OPC in young animals
(yearling rams, yearling castrated rams, and
yearling ewes) was less than 20/10,000. A
similar pattern has been observed among rams
(140/10,000) and castrated rams (55/10,000).
However, the prevalence of OvLV antibodies in
the experimental and control flocks of the
research unit was similar (22 and 25% respectively).
The rapid periodic elimination of ill
animals from the experimental flocks appears to
result in decreased OPC losses. The offspring of
these less-affected experimental flocks are being
used to repopulate other flocks in the research
unit, which may also result in diminished
disease losses. The unchanged prevalence of
OvLV in the research unit may well be related to
milk-borne transmission of the virus.
Project Achievements
The long-term study to evaluate the
possibility of reducing the prevalence of OPC
through low-cost management changes has been
completed. The value of using young, primiparous
ewes as a flock foundation and of consistently
removing clinical OPC cases from the
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