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A ProMED-mail post
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International Society for Infectious Diseases
Date: 8 May 2010
Source: En Mercopress.com [edited]
SENASA, Argentina's National Animal and Agriculture Health Board, has
issued a statement suspending all transportation of horses in the Buenos
Aires province for 2 weeks due to an outbreak of viral equine arteritis.
The ban, in force as of this week, may be extended up to 30 days and has
curtailed horse activities such as racing, show jumping, endurance, and
auctions. The origin of the outbreak was traced to semen imported recently
from Holland for jumpers.
The disease affects pregnant mares, which abort their embryos; however,
after being infected, they become immune. Stallions that have viral equine
arteritis must be gelded. The disease can be transmitted through the air or
during breeding.
According to the Merck Veterinary Manual, equine viral arteritis (EVA) is
an acute, contagious, viral disease of equids caused by equine arteritis
virus. It is characterized by fever, depression, dependent edema
(especially of the limbs, scrotum, and prepuce in the stallion),
conjunctivitis, nasal discharge, abortion and, infrequently, death in young
foals.
The virus which causes EVA was first isolated from horses in Ohio in 1953,
but the disease has afflicted equine animals worldwide for centuries. It
has been more common in some breeds of horses in the United States, but
there is no breed "immunity." There is no known human hazard.
--
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ProMED-mail
[Equine viral arteritis is caused by equine arteritis virus (EAV), an RNA
virus in the genus _Arterivirus_, family Arteriviridae and order
Nidovirales. Isolates vary in their virulence and potential to induce
abortions. Only one serotype has been recognized. Limited genetic analysis
suggests that EAV strains found among donkeys in South Africa may differ
significantly from isolates in North America and Europe.
Equine arteritis virus is found in the equidae. Antibodies to this virus
have been reported in horses, ponies, donkeys, and zebras. Illness occurs
mainly among horses and ponies, but clinical signs have also been reported
in experimentally infected donkeys. EAV might also be able to cause disease
in South American camelids: polymerase chain reaction assay (PCR) detected
viral nucleic acids in an alpaca that had aborted.
Equine arteritis virus can be transmitted by the respiratory and the
venereal routes. Acutely affected horses excrete the virus in respiratory
secretions; aerosol transmission is common when horses are gathered at
racetracks, sales, shows, and other events. This virus has also been found
in urine and feces during the acute stage. It occurs in the reproductive
tract of acutely infected mares, and both acutely and chronically infected
stallions. In mares, EAV can be found in vaginal and uterine secretions as
well as in the ovary and oviduct for a short period after infection. Mares
infected late in pregnancy may give birth to infected foals. Stallions shed
EAV in semen, and can carry the virus for years. Transmission from
stallions can occur by natural service or artificial insemination. Some
carriers may eventually clear the infection. True carrier states have not
been reported in mares, geldings or sexually immature colts; however, EAV
can occasionally be found for up to 6 months in the reproductive tract of
older prepubertal colts.
Equine arteritis virus can be transmitted on fomites including equipment,
and may be spread mechanically by humans or animals. This virus is
inactivated in 20-30 minutes at 56-58 C (133-136 F), but can remain viable
for 2 to 3 days at 37-38 C (99-100 F) and for up to 75 days at 4-8 C (39-46
F). Semen remains infectious after freezing.
The incubation period varies from 2 days to 2 weeks. Infections transmitted
venereally tend to become apparent in about one week.
Most EAV infections, especially those that occur in mares bred to long-term
carriers, are asymptomatic. The clinical signs are generally more severe in
old or very young animals and in horses that are immunocompromised or in
poor condition. Fulminant infections with severe interstitial pneumonia
and/or enteritis can be seen in foals up to a few months of age. Systemic
illness also occurs in some adults. In adult horses, the clinical signs may
include fever, depression, anorexia, limb edema (particularly in the
hindlimbs), and dependent edema of the prepuce, scrotum, mammary gland
and/or ventral body wall. Conjunctivitis, photophobia, periorbital or
supraorbital edema and rhinitis can also be seen. Some horses develop
urticaria; the hives may be localized to the head or neck, but are
sometimes generalized. Abortions or stillbirths can occur in mares that are
pregnant when they are exposed. Abortions are not necessarily preceded by
systemic signs. Temporary decreases in fertility, including reduced quality
sperm and decreased libido, may be seen in stallions during the acute stage
of the disease. The decrease in sperm quality has been attributed to
increased scrotal temperature and edema, and can persist for up to 4
months. The quality of the semen is not decreased in carrier stallions.
Except in cases of severe disease in foals, deaths are rare.
Equine viral arteritis should be considered when the clinical signs include
fever, depression, edema, conjunctivitis, nasal discharges and abortions.
This disease is difficult to differentiate from other systemic and
respiratory illnesses of horses.
The differential diagnosis includes equine influenza, equine infectious
anemia, and African horse sickness, as well as infections with Getah virus,
Hendra virus, equine rhinitis A and B viruses, equine adenoviruses, and
equine herpesviruses 1 and 4. Equine viral arteritis also resembles purpura
hemorrhagica and other streptococcal infections, as well as poisoning from
the toxic plant _Berteroa incana_ (hoary alyssum).
Acutely infected horses should be isolated to prevent transmission in
secretions and excretions. Precautions should also be taken to avoid
spreading the virus on fomites. EAV is readily inactivated by detergents,
common disinfectants and lipid solvents. No specific treatment is
available; however, most healthy horses other than young foals recover on
their own. Good nursing and symptomatic treatment should be used in severe
cases. Vaccination can also help contain outbreaks.
Venereal transmission can be controlled by good management and vaccination.
To protect pregnant mares from abortion, they should be separated from
other horses and maintained in small groups according to their predicted
foaling dates. Newly acquired horses should be isolated for 3 to 4 weeks.
Vaccination appears to prevent uninfected stallions from becoming long term
carriers. Stallions that are not carriers should be vaccinated before the
start of the breeding season. Prepubertal colts are given the vaccine when
they are 6-12 months old. Carrier stallions are identified and bred only to
well vaccinated or naturally seropositive mares. Similarly, semen that
contains EAV should be used only in these mares. Because 1st time
vaccinates may shed field viruses for a short time after exposure, these
mares should be isolated from seronegative horses, particularly pregnant
mares, for 3 weeks after breeding. Naturally infected mares and those that
are not 1st time vaccinates are isolated for 24-48 hours to protect other
horses from the viruses present in semen.
Portions of this comment have been extracted from
- Mod.TG]
[see also:
2008
---
Equine viral arteritis - Israel (02): OIE 20081111.3547
Equine viral arteritis - Israel 20081108.3515
2007
---
Equine viral arteritis - France 20070714.2260
2006
---
Equine viral arteritis - USA (NM) (02) 20061121.3317
Equine viral arteritis - USA (NM) 20060711.1903
2005
---
Equine viral arteritis - UK: OIE 20050131.0335
2002
---
Equine viral arteritis 20020209.3523
1999
---
Equine viral arteritis - New Zealand (02) 19990805.1350
Equine viral arteritis - New Zealand 19990802.1319]
...................tg/msp/sh
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