Pathogenicity and thermotolerance of entomopathogenic fungi for the control of the scab mite, Psoroptes ovis.

Psoroptes ovis is responsible for a highly contagious skin condition, both in sheep and cattle. This parasite has a marked economical impact in the sheep and cattle industry. Biological control is considered as a realistic alternative to chemotherapeutic control. Laboratory experiments were carried out to evaluate the pathogenicity and the thermotolerance of twelve isolates of entomopathogenic fungi from four genera (Beauveria Vuillemin, Metarhizium Sorokin, Paecilomyces Bainier and Verticillium Nees). The pathogenicity was evaluated by the survival of P. ovis females after exposure to 10(6) to 10(8) conidia ml(-1) in humidity chambers. Results revealed intra- and interspecies differences. All isolates with the exception of B. bassiana IHEM3558 and V. lecanii MUCL8672 induced 50% mortality within 2 days at the highest concentration. At this concentration the entire mite population became infected with all isolates but B. bassiana IHEM3558; however, only four isolates gave rise to 100% infected cadavers at the lowest concentration. The thermotolerance of each isolate was evaluated by measuring its growth on an artificial medium kept between 25 and 37.5 degrees C. All isolates were able to grow up to 30 degrees C but only two, M. anisopliae IHEM18027 and Paecilomyces farinosus MUCL18885, tolerated temperatures up to 35 degrees C. These two isolates could be considered as good candidates for further use as biopesticide taking into account their virulence and thermotolerance. Other critical factors linked with the implementation of this type of biocontrol in P. ovis infected animals are discussed.

In vitro entomopathogenic activity of Beauveria bassiana against Psoroptes spp. (Acari: Psoroptidae).

An indigenous strain (IHEM 18747) of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycetes) was evaluated for its in vitro entomopathogenic activity against the parasitic mite Psoroptes ovis Hering (Acari: Psoroptidae) from rabbits. The following aspects were evaluated: (1) effects of conidial concentration on the viability of adult females; (2) influence of the infection on the fertility, and on the hatchability of eggs; (3) and transmission of infection between mites, and from contaminated surface. Adult females immersed into increasing concentrations of conidia (10(4)-10(9)conidia ml(-1)) showed a dose-related susceptibility. At the highest concentration of conidia, LT50 was 1.6 days while LT50 of the controls reached 5.8 days. The fungus was able to sporulate on the body surface and 100% of the mites were covered with mycelium after immersion in solutions containing 10(7)-10(9)conidia ml(-1). One hundred percent of healthy mites exposed to infected cadavers or surfaces acquired the infection (LT50 reached 1.9 and 1.73 days, respectively, versus 6.1 and 5.1 days in controls, respectively). Egg laying was not reduced by the fungal infection but both the hatchability of the eggs and the life span of the emerging larvae were significantly reduced. Eggs directly infected with the fungus did not show reduced hatchability but the life span of the larvae was shortened. It is concluded that B. bassiana has a high entomopathogenic activity against Psoroptes spp. The in vivo use of this biocontrol agent against Psoroptes spp. in rabbit, sheep and cattle deserves further attention.

Comparison of three techniques for the serological diagnosis of Neospora caninum in the dog and their use for epidemiological studies.

An enzyme-linked immunosorbent assay (ELISA) was developed in our laboratory and used to determine the seroprevalence of Neospora caninum in three different dog populations in Belgium: healthy dogs from cattle farms and urban dogs with or without various neurological disorders. The test was validated and compared with two other tests: an indirect fluorescent antibody test (IFAT) and a commercially available competitive enzyme-linked immunosorbent assay (C-ELISA). The study showed a good correlation between the IFAT and the ELISA developed. When the two tests were compared with the C-ELISA, moderate positive and negative agreement indices were observed. Using our ELISA and the IFAT techniques, a high prevalence was found in farm dogs. This result showed that the neurological symptoms are not usually associated with the Neospora infection. In conclusion, the ELISA developed in our laboratory could replace the IFAT for the screening of a large number of dogs' sera.

The vertical transmission following the reactivation of a Neospora caninum chronic infection does not seem to be due to an alteration of the systemic immune response in pregnant CBA/Ca mice.

The factors responsible for the reactivation of a Neospora caninum latent infection are unknown, but it is postulated that the maternal immune response could be altered during pregnancy. The immune response was investigated in N. caninum chronically infected mice during successive pregnancies as well as in non-pregnant infected mice and mice infected when pregnant. Vertical transmission was demonstrated in chronically infected mice after the first pregnancy but the rate of foetal infection fell after further pregnancies. Non-pregnant chronically infected mice showed a marked specific proliferative response and an IgG2a isotype preferential secretion. During the course of the first pregnancy, no significant modification of the immune response was recorded. After 2 successive pregnancies, the specific cellular response showed a significant fall whereas Th2 cytokine mRNA expression was noted. At the same time, IgG1 secretion increased to reach the IgG2a level. At the third delivery, a partial restoration of the proliferative response was observed. The reactivation of N. caninum chronic infection during pregnancy does not seem to be consecutive to an immunodepression. Nevertheless, pregnancy could favour parasite multiplication in utero after an occasional spontaneous release of bradyzoites.

Fetal infection with Neospora caninum in dairy and beef cattle in Belgium.

Neospora caninum is a protozoan parasite, which causes fetal and neonatal mortality in livestock and companion animals. In 224 abortions in Belgian cattle, different diagnostic methods were used to demonstrate infection, and the presence of N. caninum. An indirect fluorescent antibody test (IFAT) was used to analyze fetal and maternal sera and immunohistochemistry (IHC) was performed when lesions consistent with neosporosis were observed in the brain, heart or liver. Twenty dairy cattle sera out of 70 (29%) and 13 beef cattle sera out of 93 (14%) were positive by IFAT. A positive titer to N. caninum was found in seven and three fetuses born to beef and dairy cows, respectively. Lesions consistent with N. caninum infection were observed in 17 fetuses. Of nine positive beef fetuses, five were confirmed by IHC while, all but one dairy fetus were confirmed using the same technique. Age had no influence on the serological status of the mother (P = 0.486) whereas husbandry system had a borderline influence (P = 0.082). However, a strong association (P = 0.004) between the level of antibodies in the dam and the occurrence of lesions in the fetus was observed and lesions were more prominent in dairy than in beef fetuses. Additionally, the distribution of intra-cerebral lesions was more extensive in dairy than in beef fetuses (P < 0.0001). Age and serological status of the fetus were found to influence the occurrence of lesions in beef fetuses (both P < 0.001) but no such significant relationships could be demonstrated in dairy fetuses. The study indicated that N. caninum must be considered as an important cause of bovine abortion in Belgium.

Humoral and cellular immune response to a crude exo-antigen and purified keratinase of Microsporum canis in experimentally infected guinea pigs.

In order to understand better the host-parasite relationship and to compare with previous observations in Microsporum canis naturally infected cats, the humoral and cellular immune responses to both a crude exo-antigen and a 31.5 kDa purified keratinase were evaluated in 12 M. canis experimentally infected guinea pigs. Humoral and cellular responses were assessed by ELISA from days 0 to 56 postinfection (PI) and by measurement of delayed-type hypersensitivity (DTH) responses on days 14 and 57 PI, respectively. Additionally, immunohistochemical staining was performed and demonstrated that the keratinase was produced in infected guinea pig skin, as previously reported in cats. Despite a marked interindividual variation, all the guinea pigs produced specific IgG to the crude exo-antigen from day 21 PI onwards, but no anti-keratinase IgG was detected. Strongly positive DTH responses to the exo-antigen were observed on both dates, whereas the keratinase elicited no and weak DTH on days 14 and 57 PI, respectively. These results are in agreement with those previously described for naturally infected cats, and indicate that the 31.5 kDa keratinase is not a major antigen in M. canis infection.

Histopathological pattern and humoral immune response to a crude exo-antigen and purified keratinase of Microsporum canis in symptomatic and asymptomatic infected cats.

In order to understand better the mechanisms involved in the diverse clinical patterns in Microsporum canis-infected cats, the histopathological features were compared in symptomatic and asymptomatic infected cats. Additionally, the IgG immune response to a crude exo-antigen and purified keratinase of M. canis was studied by ELISA in cats of various clinical and mycological status. Acute and subacute perifolliculitis and folliculitis occurred more frequently in symptomatic than asymptomatic cats. The latter usually displayed signs of chronic inflammation and a marked infiltration of superficial dermis by mast cells, which would suggest that these animals present similarities to chronically dermatophytic humans or animals. When using a crude M. canis antigen, all infected cats were shown to have significantly higher levels of specific IgG when compared to culture negative and mechanical carrier-cats. In these non-infected animals, specific IgG was more frequently detected in adults than in young animals. No difference in anti-crude antigen specific IgG was observed between symptomatic and asymptomatic infected cats, indicating that the presence of IgG is probably unrelated to the clinical status of cats. Anti-keratinase specific IgG was only detected in one of the infected cats.