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 autumn 1994, therapeutic control measures were stopped. Serological surveys were performed in the autumn of each year from 1991 until 1995. Anti-Hypoderma antibodies were found in 25%, 27.2%, 4.3%, 3.2% and 0% of the animals respectively. An experimental low infestation was conducted in the summer of 1994. During the spring 1994, third instars of Hypoderma bovis were collected from naturally infested animals. From a total of 13 pupae, six adults (four males and two females) emerged and were 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 antibody kinetics of these six animals remained parallel throughout the next 6 months: the titres increased up to April and started to fall in May to return to negative values in August. Manual examinations of the animals at weekly intervals between April and July revealed the presence of four warbled animals with one, one, two and three warbles respectively. The two other seropositive animals remained warble free. One other animal showed antibody titre fluctuations between negative and low positive values, but was warble free in the spring. In October 1995 all the animals of the herd were seronegative. The interpretation and the value of a sensitive immunodiagnosis in a large eradication programme are discussed and compared with warble counts, especially in the case of a low level of infestation.

Cross-reactive, stage-specific antigens in the Oestridae family.

The larval stages of different economically important Oestridae species were studied for their antigenicity and cross reactivity, using ELISA and immunoblotting. The immune sera of cattle from Algeria, Belgium, France and Switzerland were compared for their capacity to recognize the stage-specific antigens of their specific parasites Hypoderma bovis and H lineatum, originating from different populations. This comparison was extended to other Hypoderminae species responsible for economic losses in European animal production: H diana in roe deer and H tarandi in reindeer. The specific host for each of these parasites recognized common epitopes of hypodermin C, a collagenolytic enzyme previously well characterized in the first instar of H bovis and H lineatum. No cross reactivity was found with other Oestridae, such as Oestrus ovis or Gasterophilus intestinalis. The specificity of hypodermin C was evaluated using sera from animals harbouring other arthropods such as ticks, helminths, including Fasciola hepatica and Haemonchus contortus, or protozoa such as Anaplasma sp, and no reaction was observed. The use of hypodermin C is therefore suggested as an antigen in the immuno-survey of economically-important Hypoderminae.

[Epidemiology of bovine hypodermyiasis in canton Vaud: comparison of two methods of mapping the infestation with a view to strategic treatment]. / Epidémiologie de l'hypodermose bovine dans le Canton de Vaud: comparaison de deux méthodes de cartographie de l'infestation en vue d'un traitement stratégique.

The geographic distribution of bovine hypodermyiasis in the canton Vaud/Switzerland has been investigated in two ways: By direct examination of the animals by the livestock officers at the 1993 annual census and by ELISA on bulk milk sampled in January 1994. The efficacy of the two methods is compared and the distribution of hypodermyiasis presented on a map. The serological analyses have revealed a highly satisfactory degree of sensitivity and specificity (92.1% and 98.1%, resp.). The epidemiological interpretation however, is rather difficult, partly because quite often the animals are not infested on their farms but rather while being on alpine pastures. A monitoring of the herds with a view to an efficient control of hypodermyiasis could thus in a first instance be based on the indications provided by the livestock officers, whereas a serological monitoring in a second place would allow to detect the last and remaining foci of infestation.

Complement depletion in rats infected with Fasciola hepatica: in vivo and in vitro studies.

The action of Fasciola hepatica on rat complement was evaluated by measuring the haemolytic activity. Extracts from metacercariae and eggs and the excretory and secretory products of adult flukes reduced the classical pathway of complement-mediated lysis by normal rat sera in a protein dose-dependent manner. Whole metacercariae produced the same effect. In vitro incubation of newly excysted juveniles and intact eggs with normal rat serum had no detectable effect on serum complement activity by either the alternative or classical pathway. During the course of rat fasciolosis a depletion in the classical pathway of complement-mediated lysis was demonstrated particularly 6-9 weeks post-infection; the alternative pathway of complement-mediated lysis was not affected.

The response of cattle vaccinated with hypodermin A to a natural infestation of Hypoderma bovis and Hypoderma lineatum.

In this study, we have determined whether immunization with hypodermin A (HA), associated with various adjuvants, could provide protective immunity for calves when challenged with a natural hypoderma infestation. Groups of naive calves were vaccinated with HA antigen alone or with adjuvants [Freund's incomplete adjuvant (FIA) or alumina phosphate (AP)]. Subcutaneous injection with HA antigen with or without adjuvant did not significantly protect calves against a natural hypodermosis infestation. The humoral response during the infestation period was evaluated by ELISA. A significant earlier and greater response was induced in groups vaccinated with HA alone and HA combined with FIA. These results indicate that HA, in this vaccination protocol, induces a very incomplete protection in calves exposed to a natural infestation.

Use of pooled serum or milk samples for the epidemiological surveillance of bovine hypodermosis.

An enzyme-linked immunosorbent assay (ELISA) was used on pooled serum and milk samples to determine whether hypodermosis could be detected where a larger sero-epidemiological survey was required. This study was undertaken to assess the potential of this assay for testing sera on milk samples, pooled from 10 cows, and determining the period of the year when detection was optimal. The sensitivity of the assay was determined by increasingly diluting a positive serum with pooled negative sera, from 1:10 to 1:100. The diagnostic lower limit of the assay requires at least two serological reactors within a herd of 100. The kinetic development and depletion of anti-Hypoderma antibody of individual and pooled sera or milk from 30 cows was evaluated from November to July. Anti-Hypoderma antibody levels of two groups of 8 calves, one control and one teated with ivermectin (Ivomec), were tested from October to June. These preliminary results indicate that an ELISA assay on serum or milk samples pooled from 10 cows can be used between February and April to evaluate the prevalence of hypodermosis within cattle herds in France, demonstrating the feasibility of using pooled serum already collected for bovine leucosis testing.