Reducing transmission risk of livestock disease
New research identifies livestock husbandry practices that increase transmission risk of deadly livestock virus PPRV

Date:
August 24, 2020
Source:
Penn State
Summary:
The risk of transmitting the livestock virus PPRV, which threatens
80% of the world's sheep and goats, increases with certain husbandry
practices, including attendance at seasonal grazing camps and the
introduction of livestock to the herd.



FULL STORY ==========================================================================
The risk of transmitting the livestock virus PPRV, which threatens 80
percent of the world's sheep and goats, increases with certain husbandry practices but not herd size. A new study, led by researchers at Penn
State, investigated how transmission of PPRV might change at different
scales and identified specific husbandry practices associated with
increased odds of infection -- including the introduction of sheep and
goats to the herd, sheep or goat attendance at seasonal grazing camps,
and the sales or gifting of goats from the herd.


==========================================================================
The sheep and goat plague virus, formally known as peste des petits
ruminants virus (PPRV) and now known as small ruminant morbillivirus
(SRMV), produces a highly infectious and often fatal disease. This study,
which appears online Aug. 24 in the journal Viruses, is the third from
an international team of researchers who hope to inform strategies for
the global campaign to eradicate the virus.

"If we can identify behaviors that increase transmission risk, we can
better inform how we allocate resources to manage the virus," said
Catherine Herzog, epidemiologist and Huck postdoctoral scholar at the
Center for Infectious Disease Dynamics at Penn State and first author
of the paper.

The researchers previously found that transmission risk of PPRV was
greater among herds in pastoral villages, where people rely almost
solely on livestock for their livelihood, compared to herds from
agropastoral villages, where people rely on a mix of livestock and
agriculture. However, the factors driving these differences were unclear.

Because pastoral villages typically have much larger herds than
agropastoral villages, the researchers first investigated whether herd
size was related to the rate at which animals become infected -- the force
of infection. One might expect the rate of infection to increase with
herd size, because an animal in a larger herd would have the potential
to closely interact with more individuals.

"We hypothesized that the force of infection would increase with herd size
-- a pattern known as density-dependent transmission -- but interestingly
this is not what we observed," said Ottar Bjo/rnstad, Distinguished
Professor of Entomology and Biology and J. Lloyd and Dorothy Foehr Huck
Chair of Epidemiology at Penn State and a member of the research team.

Instead, Bjornstad explained that at the level of an individual compound,
which might contain animals from multiple households living together in
a herd, the data suggest that transmission is not related to herd size
-- a pattern known as frequency dependent transmission. The researchers
believe this is due to the formation of social cliques, whose size is unaffected by the overall herd size.

"Having a clear understanding of this relationship and if it varies
across geographic scales will improve how we model the disease," he said.

Transmission risk, however, did increase with specific husbandry practices
such as the attendance of sheep or goats at seasonal grazing camps,
where many herds come to aggregate, and introduction of livestock to the
herd. Introductions occur when animals are purchased from or returned
home from the market after a failure to sell, or if they returned
from being loaned to another herd for breeding opportunities or milk production. Transmission risk also increased when cattle or goats were
recently removed from the herd, through gifting, sale, or death.

The researchers hope their ongoing work will help clarify the ecological mechanisms driving PPRV transmission.

"Now that we have evidence that these husbandry practices are
associated with higher rates of infection in the Tanzanian setting,
we can take a closer look at these practices and recommend improvements
or modifications that could help mitigate the transmission risk," said
Herzog. "For example, we could explore quarantine procedures around the introduction of animals from sales or gifting, and the return of animals
from seasonal grazing camps. We could also focus our veterinary care on settings or events where risk is the highest."

========================================================================== Story Source: Materials provided by Penn_State. Original written by Gail McCormick. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Catherine M. Herzog, William A. de Glanville, Brian J. Willett,
Isabella
M. Cattadori, Vivek Kapur, Peter J. Hudson, Joram Buza, Emmanuel
S. Swai, Sarah Cleaveland, Ottar N. Bjo/rnstad. Peste des petits
ruminants Virus Transmission Scaling and Husbandry Practices That
Contribute to Increased Transmission Risk: An Investigation among
Sheep, Goats, and Cattle in Northern Tanzania. Viruses, 2020; 12
(9): 930 DOI: 10.3390/v12090930 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200824120042.htm

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