SERO-SURVEILLANCE OF HYPODERMOSIS IN A HERD UNDER THERAPEUTIC CONTROL- EFFECT OF A LOW-LEVEL OF INFESTATION

A cattle herd from the experimental farm of INRA in Nouzilly has been treated for hypodermosis since October 1990. Additionally, a regional eradication scheme has been implemented in this area since autumn 1992 . Bi-monthly warble counts were performed between March and July each year on an average of 200 animals. No warble was recorded in this herd from 1991 to 1994 with the exception of two dairy cows in 1993. In au tumn 1994, therapeutic control measures were stopped, Serological surv eys were performed in the autumn of each year from 1991 until 1995, An ti-Hypoderma antibodies were found in 25%, 27.2%, 4.3%, 3.2% and 0% of the animals respectively, An experimental low infestation was conduct ed in the summer of 1994. During the spring 1994, third instars of Hyp oderma bovis were collected from naturally infested animals, From a to tal of 13 pupae, six adults (four males and two females) emerged and w ere released in the herd of Nouzilly on 24 June and 4 July. In October 1994 serological investigations revealed two animals seropositive for hypodermosis. This number increased to six in January 1995. The antib ody kinetics of these six animals remained parallel throughout the nex t 6 months: the titres increased up to April and started to fall in Ma y to return to negative values in August. Manual examinations of the a nimals at weekly intervals between April and July revealed the presenc e of four warbled animals with one, one, two and three warbles respect ively. The two other seropositive animals remained warble free. One ot her animal showed antibody titre fluctuations between negative and low positive values. but was warble free in the spring. In October 1995 a ll the animals of the herd were seronegative The interpretation anti t he value of a sensitive immunodiagnosis in a large eradication program me are discussed and compared with warble counts. especially in the ca se of a low level of infestation.