Updated September 16, 2020
What Are Small Ruminant Lentiviruses (SRLV)?
SRLV are a family of viruses that affect small ruminants including sheep and goats. The most commonly known diseases caused by SRLV are CAE in goats and OPP in sheep. These viruses are in the same family as HIV, but they cannot cause HIV infections in humans.
SRLV diseases are rather common, and many animals infected can live long and enjoyable lives in spite of the diseases. Many goats in sanctuary environments are SRLV-positive. Typically, SRLV diseases are transmitted from a pregnant mother to her child while still in utero and via milk once born (known as vertical transmission), but it is also possible to transmit the disease from one animal to another via infected blood or prolonged close contact (horizontal transmission). With good care practices in place, such as not using the same needle on multiple animals, horizontal transmission of most forms of SRLV is extremely rare. Once infected, the animal carries the disease for their entire lives. There are no known cures or vaccines for SRLV diseases; preventing transmission and treating the symptoms are the best treatments available.
What Are CAE and OPP?
Caprine Arthritis and Encephalitis, or CAE, is a SRLV infection that primarily affects goats, but some variants can spread to sheep. Ovine Progressive Pneumonia, or OPP, is a disease caused by infection of an SRLV that primarily affects sheep, but some variants can be spread to goats.
How Does One Test For A SRLV?
CAE and OPP are both diagnosed and confirmed interchangeably with the same test. When new sheep or new goats arrive at your sanctuary, it’s important to have their blood tested to determine whether they have an SRLV infection. The Elisa test has been known to give false positives but is not likely to give false negatives, so one should typically trust a negative result on the test. Young goats and sheep less than six months old are not accurately testable due to their mother’s antibodies, but if they come in with a mother who is positive, it is highly likely that they are positive as well. You can also diagnose disease by tapping joints to evaluate synovial fluid, lung radiographs, mammary gland evaluation, serological testing for antibodies, or necropsies of young goats or sheep who have the Encephalitic form.
What Are The Symptoms Of CAE?
Many carriers of CAE never produce symptoms, though they still have the potential to transmit it to other residents if good care practices are not followed. Generally, symptomatic CAE animals have one of five sets of symptoms:
- Arthritic CAE: The most common form of CAE is progressive chronic arthritis, usually manifesting in animals over six months old, though sometimes there can be a sudden onset of the arthritic form. Other times, the animals will develop arthritis after seven years of age. Symptoms include arthritis in the joints, starting with inflammation and soreness in their front knees. The arthritic joints may become large and fluid-filled and typically refill after draining. Never drain their joints yourself. If a veterinarian feels a joint tap is necessary, they should perform the procedure. A joint tap done improperly can cause serious issues. Animals may not wish to stand as often as they used to, develop a limp, and avoid using their sore legs. Advanced arthritis manifests as more definitive swelling and pain in their joints. The animal’s coat becomes dull and they tend to lose weight, and they seem to generally look less healthy as the symptoms worsen.
- Encephalitic CAE: Less common than the arthritic form, the encephalitic form of CAE mostly affects young goats between 2-6 months old. The afflicted animal has poor coordination and difficulty walking, progressing into nerve damage and paralysis from the hind to front legs. It may progress further into depression, seizures, blindness, circling motions, tremors, a tilted head, and facial nerve damage. This form of CAE is unfortunately fatal.
- Pneumonic CAE: This form can be noted by a chronic cough, followed by rapid breathing, difficulty breathing in general, weight loss, pneumonia, and enlarged lymph nodes. This form seems to affect goats who are older and have been carrying the disease symptom-free for many years.
- Mastitic CAE: This form causes a hard udder that cannot produce milk. Beyond general discomfort and difficulty for an animal to nurse their young, this form of CAE does not produce many other challenges. If a kid nurses with a CAE-positive mother, they will likely get the disease as well.
- Chronic Wasting Disease: This form of CAE can be found in most CAE-positive animals. Afflicted animals progressively lose weight, generally seem less healthy than their CAE-negative counterparts, and have dull or thick and shabby coats.
What Are The Symptoms Of OPP?
OPP in sheep doesn’t typically present symptoms in sheep until around age 2 to 4. The forms of OPP are fairly similar to CAE. Generally, the affected animals first develop dull coats and lose weight, develop labored breathing due to a thickening of their lung tissue, and experience general exhaustion (sometimes they are unable to keep up with the rest of the flock). They also can commonly develop lesions on their lungs and lymph nodes, coughs and runny noses, depression, and lameness and joint deterioration in a manner similar to CAE. It can also harden udder tissue making it difficult for a sheep to nurse her lambs.
If it reaches the central nervous system, OPP can result in incoordination, head tilt, circling, twitching, and sometimes paralysis.
It appears that OPP can be spread in utero from mother to child, but more often is spread through nursing. It can be found in secretions, especially in udders and from lung discharge.
What Are The Best Treatment Options for SRLV Infections?
As there are no cures or vaccines available, it’s important to keep SRLV-positive residents who have the Pneumonic form or lung infections from SRLV-negative residents. Other forms of SRLV are not likely to spread horizontally. If you have the resources, some sanctuaries have created SRLV-positive resident herds that live completely separately from their SRLV-negative residents to be extra safe, though other sanctuaries find this to be unnecessary. No resident should ever live without at least one companion unless it’s absolutely necessary.
Regardless of whether you separate SRLV-positive residents from the rest of your herd, you should use separate needles for all residents in order to be extra vigilant in preventing the spread of disease.
If you rescue a pregnant sheep or goat who is SRLV-positive, you’ll need to consider whether or not you will allow the baby to nurse from their mother, as this is a primary source of SRLV spread. While many sources will recommend you fully separate mother and baby, another option to consider is to use a sheep or goat bra to prevent the baby from nursing, without having to separate the two. This arrangement may still cause distress for mother or baby, but will likely result in less distress than full separation. You can then milk the mother and pasteurize the milk to kill the virus or feed colostrum and milk from a non-infected source. Be sure to talk to your veterinarian to ensure you know exactly what you will need to do to protect the baby from SRLV and to protect the mother from mastitis. Because not all SRLV-positive individuals develop clinical disease, some sanctuaries choose not to intervene and instead allow the baby to nurse freely. Ultimately, this decision comes down to your Philosophy of Care.
Generally, the best you can do for infected animals is treat the symptoms as they arise. Consider the following:
- Afflicted animals might require more frequent hoof trimming due to their reluctance to move as freely as non-infected animals
- Provide ample soft bedding to prevent pressure sores in animals who prefer to lay down more often
- Keep afflicted animals from getting too cold in the wintertime
- Administer analgesics and Arthritis therapy for affected animals as necessary, although if their joints begin to break down completely or pain medication no longer seems to work effectively enough, their contentment and quality of life will unfortunately never improve much from that point onward
- Treat secondary infections with antibiotics as prescribed by your veterinarian
- Afflicted animals may be more vulnerable to other health issues such as parasitic infections
Keep a positive outlook! Just because your resident is SRLV-positive, doesn’t mean they can’t still lead a happy, comfortable life with your help.
CAE | Washington State Extension (Non-Compassionate Source)