Caprine Arthritis Encephalitis (Leukoencephalomyelitis of goats, caprine encephalomyelitis)
Caprine arthritis encephalitis (CAE) was first recognized in the early 1970's, and has emerged to be a significant and economically costly disease. The CAE virus (CAEV) is a member of the family Retroviridae, subfamily lentivirus, and hence has gained much attention as the "AIDS" virus of goats . CAEV typically infects dairy goats and is most prevalent in western countries. Caprine arthritis encephalitis has emerged to become one of the five most important diseases of dairy goats in the western hemisphere and such should be perceived as a major threat to the goat industry.CAEV creates a persistent infection which may regress but will invariably worsen with time, and although CAE is detected in a goat it is not automatic grounds for euthanasia. There is no cure and supportive therapy is the only course of action. This includes good nutrition, nursing care, palliative measures and phenylbutazone to decrease discomfort.
Arthritis is the most common form of CAE.
The CAE virus (CAEV) is a member of the family Retroviridae, subfamily lentivirus. Seroprevalence ranges from 38% to 81% in the USA, Canada and Europe. In England, Australia and developing contries is less than 10%.Clinical arthritis will develop in 25 % of seropositive goats.
CAEV presents itself in goats in 5 clinical forms: the arthritic form affecting older goats; the neurologic form affecting goats from 2-6 months; the respiratory form which manifests itself as a chronic progressive interstitial pneumonia in adults (and may be associated with arthritis); the udder form, an indurative viral mastitis; and the chronic wasting form. 1)The arthritic form, commonly known as "big knee", tends to affect dairy goats which are sexually mature and are one or more years of age. The arthritis tends to be insidious in onset and manifests itself either acutely or chronically. All joints exhibit signs of arthritis but the most commonly affected joints are the carpus, followed by the tarsus, stifle and fetlock. Early signs are quite subtle and may vary from reluctance to move to decreased feeding. The joints are frequently swollen due to increased synovial fluid and are cool to the touch. The disease often cycles and affected goats may enter periods of remission. However, the disease always progresses to a debilitating stage characterized by weight and hair loss. Pain becomes apparent due to progressive mineralization of the capsule and soft tissue surrounding the joint, and exostoses of the bone causing collapse of the joint which can be demonstrated by a radiograph. 2) The neurologic form tends to affect dairy goats between 2-6 months of age, but has been known to affect goats of any age. Clinical signs vary greatly between the cases but most patients show ataxia and then progressive paresis, beginning in the hindlimbs and extending to the forelimbs. Gait abnormalities will depend on the site of the spinal cord affected. Other signs which are transient and recurring may include increase in temperature (mild to severe), depression, blindness, abnormal pupillary light reflex, lack of menace response, abnormal nystagmus, opisthotonos, head tremor, head tilt, circle and others. The virus favours the white matter of the spinal cord which results in hypertonic hyperactive patellar reflexes in one or more legs. However, if the infection is severe enough, it may extend into the grey matter and produce hyperactive reflexes. The final culmination is seizuring and death, but up until that point, kids remain alert and nonfebrile.3) Mastitis caused by CAE is often referred to as "hard udder" due to the firm appearance of the udder during infection. This disease has not been proven to be caused exclusively by CAE, but experimental infection of goats with CAE produces the symptoms of hard indurative viral mastitis.. Goats with this condition have rock-like udders which have a non-edematous outer skin layer. The udder is cool, and erythema is absent. Milk is difficult to express from the udder and when it is, there is an increase in cell count. The supra mammary lymph nodes are enlarged but there is no other evidence of systemic viral disease. 4) The pneumonic form, which may be subclinical or fatal, may accompany the CNS form or exist by itself. Whether or not CAE can produce these signs by itself, or whether it needs a helper virus to achieve its' effects is still unknown as experimental infection will not produce the same pneumonia. However, it is known that lung worm infection can precipitate the pneumonic form by causing a macrophage proliferation. Pneumonic CAE manifests itself after a stressful event and produces dyspnea, exercise intolerance, wasting and a chronic cough. Often, secondary bacterial infections produce a greater degree of disease and antibiotic treatment may be of some use. Some goats may have enlarged carpi, but this is not always present. 5) Chronic weight loss in goats is another manifestation of CAE. It may accompany the arthritic or pneumonic form and may also exist by itself. CAE is present for life and chronic weight loss may be due to persistent cytokine release, and may be independent of feed intake.
Clinical and Pathologic Features
The development of the disease is similar to Maedi/Visna. Virus replicates in macrophages and CMI responses contribute to the lesions. Chronic connective tissue disease affects the joints of mature goats; a leukoencephalomyelitis is seen in young goats and less commonly there is mastitis or pneumonia in older goats.The arthritic form is characterized by a proliferative synovitis of the carpal, fetlock, hock, and stifle joints. Joints are enlarged, especially the carpal joints, and common histological lesions are those of synovial cell proliferation and inflammatory cell infiltration (lymphocytes, plasma cells, and macrophages). The arthritis may remain static or become progressively worse with development of fibrinous concretion, necrosis, and mineralization.
Central nervous system (CNS) disease is principally seen in young kids 2 - 4 months of age and is characterized by a progressive ascending paralysis. Microscopically, the CNS lesions resemble those of Visna in sheep and include lymphocytic cell infiltration and demyelination of the white matter.Some infected goats may develop an interstitial pneumonitis and some infected does may develop swollen, fibrotic mammary glands.
CAE is a chronic disease of multiple organ systems. 75% of seropositive animals will stay without any clinical signs.
Symproms can be classified in 4 clinical syndromes.
Chronic arthritis is seen in goats older than 6 months.
Caprine arthritis encephalitis virus; a non
- oncogenic retrovirus of the genus Lentivirus. As mentioned earlier, this virus is closely related antigenically to the virus causing Maedi/Visna.
- encephalitis (CAE) virus is widely distributed in goats of all ages and breeds throughout the world. The disease is seen most frequently in dairy goats.
Young kids are most commonly infected through the ingestion of milk from infected does. Horizontal transmission is thought to occur by direct contact with secretions and excretions from infected goats and through coitus.
The pathogenesis of the disease is similar to Maedi/Visna. It is characterized by chronic persistent inflammation, which is not resolved in spite of a vigorous CMI response to viral antigen. Infected monocytes are a source of persistent antigen and a large number of viral variants generated during viral replication; this combination contributes to the inability of the host to resolve the infection. Immunopathologic mechanisms are thought to be responsible for the development of most lesions.
Diagnosis can be difficult as goats may be infected with CAEV but never show clinical manifestations of the disease. In addition, CAE has many differential diagnoses. For example, bacterial infection or copper deficiency can cause a similar form of arthritis to that seen in CAE. The neurological form can be confused with congenital malformations, trauma, vertebral body abscess, polioencephalomalacia, and or listeriosis.
The first step in diagnosing CAE is to rule out bacterial infection, such as mycoplasma, chlamydia, erysipelas and listeria.
Lung. Loose perivascular lymphoid nodule and cuboidal hyperplasia of type II pneumoncytes in some alveoli. The alveoli are filled with dense eosinophilic proteinaceous material and occasional histiocytes.
In chronic arthritis synovial fluid has a decreased protein concentration and has more lymphocytes.
- Anorexia, loss or decreased appetite, not nursing, off feed
- Dysphagia, difficulty swallowing
- Abnormal proprioceptive positioning, knuckling
- Ataxia, incoordination, staggering, falling
- Dysmetria, hypermetria, hypometria
- Exercise intolerance, tires easily
- Fever, pyrexia, hyperthermia
- Forelimb atrophy, wasting
- Forelimb lameness, stiffness, limping fore leg
- Forelimb swelling, mass in fore leg joint and/or non-joint area
- Forelimb weakness, paresis, paralysis front leg
- Generalized lameness or stiffness, limping
- Generalized weakness, paresis, paralysis
- Head, face, ears, jaw weakness, droop, paresis, paralysis
- Hindlimb atrophy, wasting
- Hindlimb lameness, stiffness, limping hind leg
- Hindlimb swelling, mass in hind leg joint and/or non-joint area
- Inability to stand, downer, prostration
- Mammary gland swelling, mass, hypertrophy udder, gynecomastia
- Paraparesis, weakness, paralysis both hind limbs
- Tetraparesis, weakness, paralysis all four limbs
- Torticollis, twisted neck
- Trembling, shivering, fasciculations, chilling
- Underweight, poor condition, thin, emaciated, unthriftiness, ill thrift
- Weakness of one hindlimb, paresis paralysis rear leg
- Weight loss
- Decreased mobility of forelimb joint, arthrogryposis front leg
- Decreased mobility of hindlimb joint, arthrogryposis rear leg
- Abnormal behavior, aggression, changing habits
- Abnormal forelimb reflexes, increased or decreased
- Abnormal hindlimb reflexes, increased or decreased
- Dullness, depression, lethargy, depressed, lethargic, listless
- Forelimb hypoesthesia, anesthesia front leg
- Head, face, neck, tongue hypoesthesia, anesthesia
- Head tilt
- Hindlimb hypoesthesia, anesthesia rear leg
- Hyperesthesia, irritable, hyperactive
- Abnormal pupillary response to light
- Agalactia, decreased, absent milk production
- Anestrus, absence of reproductive cycle, no visible estrus
- Firm mammary gland, hard udder
- Coughing, coughs
- Dyspnea, difficult, open mouth breathing, grunt, gasping
- Increased respiratory rate, polypnea, tachypnea, hyperpnea
- Rough hair coat, dull, standing on end
As no treatment or vaccine is available for CAEV, control of it's spread depends on development of a prevention program that aims at reducing the risk factors described in modes of transmission .
1) Prevent the transfer of infection through the milk of infected does by removing kids from dams immediately at birth and feeding the kids either: pasteurized goat colostrum and milk, or cow's colostrum and milk.
2) Reduce the risk of horizontal transmission by removing seropositive goats from contact with seronegative goats.
IMPORTANT: The goal of a control program is to prevent contact of goats with potential sources of the virus. As this is repeated over several generations, the incidence and risk of CAE virus exposure within a farm should decrease, as will the likelihood of contact with an infected goat or milk from an infected doe
- Goats infected with CAE virus remain infected for life.
- Prevention is best accomplished by maintaining closed herds.
- All replacement animals should be isolated and tested serologically (ELISA or AGID).
- Control of CAE in herds in which the virus is enzootic is difficult. If economically feasible, test and removal is the preferred method. Alternatively, serologically positive animals should be segregated from negative animals. Young kids should be removed from positive does at birth.
- Milk from infected does should not be fed unless it has been pasteurized.