Indian Farmer, Vol.

8 (03); March-2021 Gomes et al

Volume 8, Issue 03, 2021, Pp. 273-277.

ORIGINAL ARTICLE

Viral diseases of sheep and goats

Amitha Reena Gomes., Kavitha G., Sumathi, B. R and Saritha N. S

IAH & VB, Hebbal, Bangalore-24

S
mall ruminants are an important source of meat, milk or wool throughout the
world. Sheep and goats are both small ruminants with cosmopolitan
distributions due to their being kept as grazers both individually and in herds in
return for their production of milk, wool, and meat. As such the diseases of these
animals are of great economic importance to humans. This article describes the diseases
of sheep and goats in India in brief with special reference to their etiology, clinical signs,
treatment, prevention and control.
1. Contagious ecthyma (orf)
Orf is an exanthemous and highly contagious disease caused by a parapox
virus and occurring primarily in sheep and goats. It is also known as contagious
pustular dermatitis, infectious labial dermatitis, ecthyma contagiosum, thistle
disease and scabby mouth. Orf virus is zoonotic, it can also infect humans. The disease is
manifested by the occurrence of the pustular and scabby lesions on the lips, muzzle and
udder. The disease is endemic worldwide. Incubation period of the disease is 2 - 3 days.
Symptoms include papules and pustules on the lips and muzzle, and less
commonly in the mouth of young lambs and on the eyelids, feet, and teats of ewes. The
lesions progress to thick crusts which may bleed. Orf in the mouths of lambs may
prevent suckling and cause weight loss, and can infect the udder of the mother ewe,
thus potentially leading to mastitis. Sheep are prone to reinfection. Occasionally the
infection can be extensive and persistent if the animal does not produce an immune
response.
The disease is transmitted by direct contact between animals and indirect
contact with dry scabs in pens. The virus is resistant to drying and may be viable in
scabs for months and years in empty feedlots and pens. Farm workers may disseminate
the virus among animals of different pens with contaminated equipment, feed and farm
vehicles.

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More typically the infected animal will become free of orf within a week or so as
the disease runs its course. Sheep custodians can assist by ensuring infected lambs
receive sufficient milk and separating out the infected stock to slow down cross-
transmission to healthy animals. The topical application of antiseptics, may reduce
bacterial contamination of the lesions and help prevent secondary complications. Live
attenuated orf vaccine can be used to prevent the disease. Bluetongue, foot and mouth
disease, sheep and goat pox, ulcerative dermatosis, cutaneous anthrax and vesicular
diseases are some of the diseases to be considered in differential diagnosis.
2. Bluetongue (BT)
Blue tongue is a non-contagious, insect-borne, viral disease of ruminants,
mainly sheep and less frequently cattle, goats, buffalo, deer, dromedaries, and antelope.
It is caused by the Bluetongue virus (BTV). The virus is transmitted by
the midge Culicoides imicola, Culicoides variipennis, and other culicoids. The disease is
manifested by fever, oral lesions, lameness and emaciation. The disease is also known as
catarrhal fever of sheep or soremuzzle disease. The disease occurs mostly in the African
region, in Asia and the Pacific and in the Western hemisphere.
In sheep, BTV causes an acute disease with high morbidity and mortality.
Major signs are high fever, excessive salivation, swelling of the face and tongue
and cyanosis of the tongue. Swelling of the lips and tongue gives the tongue its typical
blue appearance, though this sign is confined to a minority of the animals. Nasal signs
may be prominent, with nasal discharge and stertorous respiration. Some animals also
develop foot lesions, beginning with coronitis, with consequent lameness. In sheep, this
can lead to knee-walking. Torsion of the neck (opisthotonos or torticollis) is observed in
severely affected animals. Not all animals develop signs, but all those that do lose
condition rapidly, and the sickest die within a week. For affected animals which do not
die, recovery is very slow, lasting several months. The incubation period is 5–20 days,
and all signs usually develop within a month. In goats and wild ruminants infection is
usually asymptomatic despite high virus levels in blood.
Treatment and prevention is effected via quarantine, vaccination and control of
the midge vector. Simple husbandry changes and practical midge control measures may
help break the livestock infection cycle. Housing livestock during times of maximum
midge activity (from dusk to dawn) may lead to significantly reduced biting rates.
Similarly, protecting livestock shelters with fine mesh netting or coarser material
impregnated with insecticide will reduce contact with the midges.
The culicoides midges that carry the virus usually breed on animal dung and moist soils,
either bare or covered in short grass. Identifying breeding grounds and breaking the
breeding cycle will significantly reduce the local midge population. Turning off taps,
mending leaks and filling in or draining damp areas will also help dry up breeding
sites. There are no medications available to treat the disease, but supportive treatment
may decrease mortality.
Even though there are more than 24 serotypes reported only 5 serotypes are
more prevelant. Therefore bluetongue multivalent inactivated vaccine is introduced

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with BTV serotypes 1, 2, 10, 16 and 23 which are prevalent in India. The vaccination of
sheep needs to be done one month before the onset of monsoon.
3. Peste des petits ruminants
Peste des petits ruminants (PPR), also known as ‘goat plague’, is a viral disease of
goats and sheep characterized by fever, sores in the mouth, diarrhea, pneumonia, and
sometimes death. It is caused by a morbillivirus in the family of paramyxoviruses, that is
related to rinderpest, measles and canine distemper. Cattle and several wild ruminants
have been infected most often experimentally, but goats and sheep are the usual targets.
The virus is secreted in tears, nasal discharge, secretions from coughing, and in
the faeces of infected animals. Therefore, close contact between animals, especially
through inhalation of fine droplets that are released into the air when affected animals
cough and sneeze will spread the disease. Water, feed troughs, and bedding can also be
contaminated with secretions and become additional sources of infection, however the
virus does not survive for a long time outside the body of a host animal. Since animals
excrete the virus before showing signs of the disease, it can spread by movement of
infected animals.
After an incubation period of 3-6 days, there is a sudden onset of fever, severe
depression, loss of appetite, and clear nasal discharge. The nasal discharge becomes
thicker and yellow, often becoming so profuse that it forms a crust that blocks the
nostrils causing respiratory distress. The eyes may also become infected, causing
eyelids to mat together with discharge. Tissues in the mouth can swell and ulcers form
on the lower gums, dental pad, hard palate, cheeks and tongue. Severe diarrhoea
develops in some animals, resulting in dehydration and weight loss. Pneumonia is
common in later stages. Pregnant animals may abort. The prognosis of peste des petits
ruminants is poor and death can occur within five to ten days of the onset of fever.
Young animals are most severely affected, goats more than sheep. In its most severe
form (peracute) animals are found dead. However, the disease can be mild or
unapparent and circulate in a country causing little or no illness until susceptible goats
are exposed.
When the disease appears, the standard disease control measures consisting of
quarantine, movement control, sanitary slaughter, and cleaning and disinfection are
applied. The virus is susceptible to most disinfectants. There are no medications
available to treat the disease, but supportive treatment may decrease mortality. A live
attenuated homologous vaccine is used through out India and it provides good
immunity.
4. Sheep and goat pox
Sheeppox and goatpox are serious, often fatal, diseases characterized by
widespread skin eruption. The poxviruses of sheep and goats (capripoxviruses) are
closely related, both antigenically and physicochemically. Reports on the natural
susceptibility of sheep to the virus of goatpox and vice versa are conflicting; at least
some strains seem capable of infecting both species.

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The incubation period of sheeppox is 4–8 days and that of goat pox is 5–14 days.
The clinical picture is similar in the two diseases but is generally less severe in goats.
Fever and a variable degree of systemic disturbance develop. Eyelids become swollen,
and mucopurulent discharge crusts the nostrils. Widespread skin lesions develop and
are most readily seen on the muzzle, ears, and areas free of wool or long hair. Palpation
can detect lesions not readily seen. Lesions start as erythematous areas on the skin and
progress rapidly to raised, circular plaques with congested borders caused by local
inflammation, edema, and epithelial hyperplasia. Although microvesicles are present
histologically, vesicles and pustules are not evident clinically. Virus is abundant in skin
lesions at this stage. As lesions start to regress, necrosis of the dermis occurs and dark,
hard scabs form, which are sharply separated from the surrounding skin. Regeneration
of the epithelium beneath the scabs takes several weeks. When scabs are removed, a
star-shaped scar, free of hair or wool, remains. In severe cases, lesions can develop in
the lungs. In some sheep and in certain breeds, the disease may be mild or the infection
inapparent.
The disease is often transmitted by the respiratory route during close contact,
but they may also enter the body through other mucous membranes or abraded skin.
These viruses can be found in saliva, nasal and conjunctival secretions, milk, urine and
feces, as well as in skin lesions and their scabs. Ulcers on the mucous membranes are
important sources of virus. The virus can also be spread on fomites or transmitted
mechanically by insects such as stable flies (Stomoxys calcitrans), although the latter
route may be uncommon. These viruses can remain infectious for up to six months in
shaded sheep pens. They may also be found on the wool or hair for as long as three
months after infection, and possibly longer in scabs.
Outbreaks can be controlled by quarantines, movement controls, and
depopulation of infected and exposed animals, followed by stringent cleaning and
disinfection of farms and equipment. Proper disposal of infected carcasses is important;
burning or burial is often used. Capripoxviruses may persist for up to 6 months in
shaded, uncleaned pens and for at least a few months in dry scabs on skin, fleece and
hair.
In endemic area systematic vaccination programs have provided the most
effective control over the disease. Cell cultured attenuated vaccines which give good
immunity are used to prevent the disease.
5. Foot and mouth disease
Foot and Mouth Disease (FMD) is a severe, highly contagious viral disease of
livestock with significant economic impact. The disease affects cattle and swine as well
as sheep, goats, and other cloven-hoofed ruminants. Sheep and goats play an important
role in the epidemiology and transmission of FMD. Typical clinical signs of FMD in sheep
and goats include pyrexia, lameness and oral lesions, which are often mild, foot lesions
along the coronary band or interdigital spaces, and lesions on the dental pad, which may
go unrecognised, agalactia in milking sheep and goats and death of young stock without
clinical signs. FMD is difficult to diagnose in small ruminants as infected sheep not

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always show typical clinical symptoms or as the cardinal signs mimicked other diseases.
Sheep and goats may be carriers. Infected herds which practice transhumance or are
nomadic can spread the infection to other herds long before diagnose of the disease is
established. Shipping and trade with live sheep and goats is much more common world
wide than in other FMD susceptible species. Lack of identification of all sheep and goat
herds and lack of individual identifications signs may result in incomplete control
measurements under FMD conditions.
In a susceptible population, morbidity approaches 100%. Intensively reared
animals are more susceptible to the disease than traditional breeds. The organism
which causes FMD is an aphthovirus of the family Picornaviridae. There are seven
strains (A, O, C, SAT1, SAT2, SAT3, Asia1) each one requiring a specific vaccine strain to
provide immunity to a vaccinated animal.
FMD viruses can be spread by animals, people, or materials that bring the virus
into physical contact with susceptible animals. FMD is found in all excretions and
secretions from an infected animal. Infected animals notably breathe out a large amount
of aerosolized virus, which can infect other animals via the respiratory or oral routes.
The disease can be treated for secondary bacterial infections. The lesions can be
washed with one per cent potassium permanganate solution. Antiseptic lotion can be
applied to the vesicles on the foot. Boric acid and glycerine paste can be applied to the
oral lesions. Diseased animals should be fed on a palliative diet and should be
segregated from the heard of healthy animals. Healthy animals can be vaccinated with
the inactivated vaccine as a preventive measure.
To conclude, maintaining the health of sheep and goats with a strict vaccination
program, having effective parasite control program, quarantining new additions to the
herd for at least three weeks, providing adequate nutrition for optimal reproductive
capability and to reduce susceptibility to disease and parasitism and maintaining clean,
well-ventilated housing will avoid many health problems.

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