Understanding Caev: a sneaky virus that takes root and mutates
The disease ofviral caprine arthritis-encephalitis (AECV or Caev in its English acronym) is caused by a RNA virus (retrovirus). This type of virus manages to integrate into the genome of the host cell. This integration makes the infection irreversible. Carrier animals cannot not get rid of the virus. Once integrated into the host’s cells, the virus remains hidden from the immune system for a more or less long time, which means that a goat may be HIV negative but infected. THE Caev is a virus lent (lentivirus) which takes a few months, or even a few years, to express itself. “This complicates early diagnosis and gives the virus time to spread within the herdcomments Carole Sala, consulting veterinarian at GDS France. This slow evolution can mislead breeders. They think the herd is healthy when the disease progresses silently. »
The Caev is also known for its strong ability to mutate. “There exists many strains and it is this variability which prevents the development of an effective vaccineunderlines Carole Sala. The animal’s immune response also always lags, because the antibodies produced often do not match the new mutations. » An animal sick with Caev will therefore not be able to recover..
The different strains have a variable pathogenicity : some can circulate silently, while others cause severe clinical forms. This is why breeders of infected herds with few or no clinical signs should stay vigilant pour do not introduce more virulent strains.
Serology possible by mixing five samples
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To diagnose the presence of Caev in a herd, the only accessible method remains the serology. It is based on the detection of antibodies produced by the immune system during contact with the virus, even if the animal is asymptomatic. THE kits de diagnostic currently available have a sensitivity and specificity of around 97%, thus offering a good capacity to detect infected animals while limiting false positive results.
Since July 2024, it is possible to carry out Caev serologies by pooling the sera from five animals in the same test. This approach maintains high sensitivity and specificity, equivalent to those of individual tests, while dividing analysis costs by two or even three.
The virology by PCR which consists of searching for the genetic material of Caev is currently only carried out within the framework of research by a single INRAE laboratory in Lyon. A promising avenue remains serology on tank milk since it gives an overall estimate of seroprevalence in the herd from a single analysis. This method is still being tested (Serocaptank) to improve the interpretation of the results.
Big knees, the most specific sign of Caev
THE clinical signs the most common are arthritis (inflammation of the joints), indurated udders (“wood udders”) or unbalanced and progressive losses of state. Among the kidsof the encephalitis Acute illnesses can occur and lead irremediably to the death of the animal. They result in nervous signs such as convulsions or lack of coordination.
The most characteristic sign remains theknee arthritis (front legs). These clinical signs lead after a few months to reform lame or unproductive animals.
The economic burden of Caev: at least 93 euros per goat
In addition to animal suffering, Caev leads to significant economic losses : reduction in milk production and milk quality and premature culling of animals. A French study showed an average loss of milk production of more than 100 kilos per goat per year, beyond the third lactation in infected herds.
Taking into account this loss of production, chronic mastitis, a drop in useful material and indirect costs for the breeding of replacement goats, Bertrand Bluet of the Livestock Institute estimates a loss ofat least 93 euros per goat for positive herds.
Caev is transmitted through colostrum, milk or air
In young animals, the Caev is transmitted mainly by colostrum and the lait of the infected goats. As animals grow, the transmission will essentially be done by respiratory routeduring close contact or in poorly ventilated buildings via infected aerosols. Carole Sala explains: “All infected animals, even those that are seronegative, are contagious. The more clinical signs an animal shows, the more infectious it is to others. » The virus can also be transmitted through the semen of infected goats or through improper care practices, such as the use of unexchanged needles between animals.
This diversity of transmission modes makes the mastery of Caev particularly complexbecause it can spread quickly within a poorly protected herd. Carole Sala insists: “Caev is everywhere: in milk, respiratory secretions, blood… This is why it is essential to respect strict measures of biosecurity to limit its spread in the herd. »
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