Immunoblotting analysis of somatic components of Dirofilaria immitis

SDS-PAGE analysis of Dirofilaria immitis extracts demonstrated the complexicity of protein components of microfilariae, similar to that of adult male and female worms. Immunoblotting analysis using sera from microfilaremic and amicrofilaremic dogs with D. immitis infection suggest that antigenic components in the low molecular weight region may be related to the anti-microfilarial mechanism of the host.

Clinical prophylactic activity of melarsomine dihydrochloride (RM 340) against Dirofilaria immitis in heartworm-naive beagles exposed to natural infection in three southeastern states

Melarsomine dihydrochloride (RM 340), a drug being developed as an adulticide for treatment of heartworm (Dirofilaria immitis) infection in dogs, was safe and highly effective as a clinical prophylactic agent against naturally acquired infections using Strategic and Tactical Treatment Programs. The Strategic Program involved treatment every 4 months (three series of treatments per year), disregarding the mosquito season (MS), to clear the existing infection at each treatment. The Tactical Program consisted of two series of treatments per year, 4 months apart, with the first one given about the middle of the MS (August) and the second one given after the end of the MS (December). Melarsomine was administered as two i.m. injections (lumbar muscles) of 2.2 mg kg-1 given 3 h apart. A total of 90 heartworm-naive beagles and a number of microfilaremic 'seed' dogs were used. Three similar experiments (30 beagles per experiment) were conducted at selected areas (Georgia, Florida, Louisiana) known to be enzootic for heartworm. At each site, 30 beagles were allocated to six groups of five dogs each, and four of these groups were placed outdoors in April of 1988. Two groups (control and treated) were exposed for 12 months, and the treated group was given melarsomine at 4, 8, and 12 months after exposure was started (Strategic Program). Another group was exposed for 8 months and treated with melarsomine at 4 and 8 months (Tactical Program). One group of tracer (sentinel) beagles was exposed from April to August 1988, one group from August to December 1988, and another from December 1988 to April 1989. April-August and August-December tracers served as controls for the tactically treated dogs. After exposure, all dogs were held indoors for 5 months before necropsy. Blood was collected at 4-5 month intervals and examined for microfilariae (MF) and adult heartworm antigen (enzyme-linked immunosorbent assay, ELISA). Treatment by the Strategic Program was 99% effective, with only one of the total of 15 treated dogs harboring any worms (a single female) at necropsy. Thirteen of the 14 control dogs (93%) exposed for 12 months became infected, with average worm recoveries of 6.8, 5.4, and 25.2 (range 1-45) for the Georgia, Florida, and Louisiana sites, respectively. All of the 13 heartworm-infected control dogs were antigen-positive, and 12 of these were also MF-positive, while none of the strategically treated dogs was either antigen- or MF-positive at necropsy. Tactical treatment of the total of 14 dogs twice per year was 100% effective.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of melarsomine dihydrochloride (RM 340) for adulticidal treatment of dogs with naturally acquired infections of Dirofilaria immitis and for clinical prophylaxis during reexposure for 1 year

Heartworm-infected dogs were treated therapeutically with a new heartworm adulticide (melarsomine dihydrochloride, RM 340) and then put on a Strategic Program with treatment every 4 months for clinical prophylaxis to take advantage of the drug's potent activity against 4-month-old immature as well as adult Dirofilaria immitis. Ten random-source dogs with naturally acquired heartworm infections (microfilariae- and antigen-positive) were given melarsomine (2.2 mg kg-1 twice 3 h apart) by i.m. injection in the lumbar muscles to clear their existing infections. They were then placed outdoors (August 1988) in a high-risk area in Georgia (USA) for heartworm transmission and given melarsomine at the same posology every 4 months (Strategic Program) for 12 months as a clinical prophylactic measure. Five nontreated heartworm-naive beagles placed at this site during the same period served as 'controls' to monitor heartworm transmission. After exposure for 12 months, the ten treated and five 'control' dogs were taken indoors and held for 5 months. Microfilaremia and antigenemia levels were monitored in both groups by testing at 4-5 month intervals throughout the study and the intensity of infection was determined at necropsy. Microfilaremia levels in treated dogs dropped dramatically following the initial therapeutic treatment and remained either negative or low. Only two of the five 'control' dogs became microfilaremic, and this occurred near the end of the study. Nine of the ten treated dogs were antigen-negative 4 months after the initial therapeutic treatment, and all of them were antigen-negative at all bleedings thereafter. Four of the five 'control' dogs were antigen-positive at necropsy, and only one of these was positive 4 months earlier. Based on these antigen data, the initial treatment cleared 90% of the dogs of worms, and no worms were detected in any of the treated dogs thereafter. However, it is possible that undetectable immature heartworms were present. Although all of the treated dogs were antigen-negative at necropsy, three of them had a total of eight heartworms, seven of which were clearly immature, as determined by worm length measurements, and the remaining worm was a young adult female that was probably too young to be detected. All of the five 'control' dogs had heartworms (average 7.4; range 1-16), and about half of these worms were clearly immatures. Therapeutic treatment followed by strategic treatment with melarsomine every 4 months during reexposure was at least 89.2% effective overall.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantification of serum total IgE concentration in dogs by use of an enzyme-linked immunosorbent assay containing monoclonal murine anti-canine IgE

A method for quantification of serum total IgE concentration in dogs by use of an ELISA containing monoclonal mouse anti-canine IgE was developed. Microtitration plates were coated with monoclonal mouse anti-canine IgE. Test sera and reference serum dilutions were added, followed by biotinylated monoclonal mouse anti-canine IgE. Avidin-alkaline phosphatase conjugate was added, and color development was measured spectrophotometrically, using a microtitration plate reader. Quantitative results were obtained by assigning to a reference serum a value of 100 IgE units/ml. Absorbance values of unknown samples were converted into IgE units by comparison with a standard curve generated by measurement of reference serum dilutions. Intra- and interassay coefficients of variation were 5 and 7%, respectively, and assay sensitivity was 1 U/ml. The assay was used to establish a normal range for total IgE concentrations in 30 healthy dogs. Total IgE concentration in healthy dogs followed a skewed distribution and ranged from < 1 to 91.2 U/ml, with a geometric mean value of 7.1 U/ml. The IgE concentration was remarkably stable in serum samples subjected to 25 freeze/thaw cycles or incubation at approximately 25 C (room temperature) for up to 10 days. Comparison of total IgE concentrations in 23 serum samples assayed by use of double-overlay radial immunodiffusion and ELISA yielded correlation coefficient of 0.94. Comparison of the reference serum standard curve with serial dilutions of a purified IgE solution of known concentration yielded a range of values for the IgE unit of 0.7 to 2.0 micrograms.

Expression of an Onchocerca volvulus Ov33 homolog in Dirofilaria immitis: potential in immunodiagnosis of heartworm infection

In this study, the expression of an Onchocerca volvulus Ov33 homolog was demonstrated in Dirofilaria immitis. Rabbit antiserum raised against a recombinant fusion protein of O. volvulus, MBP/OvD 5B (Ov33), was found to react with a 31-33 kDa glycoprotein (DiT33) of adult worms of D. immitis. An antibody response to MBP/OvD 5B was observed in dogs, as early as 11 weeks post infection with infective larvae of D. immitis, and in dogs with occult infection. Cats both experimentally and naturally infected with D. immitis also reacted strongly with the recombinant antigen. In contrast, sera from dogs receiving chemically-abbreviated infection or from animals harbouring a variety of other helminths failed to react. These data suggest that antibody responses generated by DiT33 may have potential in immunodiagnosis of heartworm infection in cats and dogs.

[Human dirofilariasis: identification of a 44kD antigen recognized by IgM against Dirofilaria immitis]

BACKGROUND

Dirofilaria immitis is a nematode parasite of canids that, in endemic areas, can infect humans. The use of adult somatic antigens for the diagnosis of human dirofilariasis has the disadvantage of a low sensibility because of cross-reactivity with other helminths, specially with IgM antibodies. We describe in this work proteins of the adult somatic antigenic complex that are specifically recognized by human IgM.

METHODS

Human sera with different characteristics were analyzed by an enzyme-linked immunosorbent assay (ELISA) for the detection of anti-D. immitis IgM seropositive individuals. Moreover, an enzyme-linked immuno-electro-transfer blot (EITB) was performed for the detection of polypeptides that specifically react with IgM anti-D. immitis.

RESULTS

EITB analysis shows that 2 proteins of 44 and 18 kD are recognized by IgM in human sera from an endemic area with a high antibody titer against D. immitis measured by ELISA. Sera from a non-endemic area and from patients suffering from other parasitic and non-parasitic diseases did not recognize these antigens.

CONCLUSIONS

We believe that the 44 kD protein could be a good marker of recent D. immitis infection.

An analysis of the humoral immune response of dogs following vaccination with irradiated infective larvae of Dirofilaria immitis

In this study, dogs were immunized with irradiated L3 larvae of Dirofilaria immitis. Following challenge with non-irradiated L3, vaccinated dogs had an average of 71% fewer adult worms compared to non-vaccinated animals. A comparative analysis of eosinophil and antibody responses of these two groups of dogs is presented. Vaccinated dogs preferentially recognized several larval (14, 20, 30, 34, 39 kDa), adult worm (20 kDa) and microfilarial (36, 38, 71, 84 kDa) antigens. To characterize these antigens, the extent of glycosylation was assessed. The data suggest that an earlier response to these antigens may be important in the protection induced in dogs by administration of irradiated L3 of D. immitis.

Molecular cloning and characterization of a novel neutrophil chemotactic factor from a filarial parasite

To compare the molecular structure of a parasite-derived neutrophil chemotactic factor (NCF) with host-derived NCFs or other NCFs, molecular cloning of cDNA encoding NCF derived from Dirofilaria immitis adult worm (DiNCF) was performed. A D. immitis cDNA library was screened with an antibody to DiNCF, and one DiNCF cDNA clone (pD-4) was isolated. A fusion protein of pD-4 and gene 10 protein showed significant neutrophil chemotactic activity whereas gene 10 protein itself showed marginal neutrophil chemotactic activity. The total nucleotide sequence analysis revealed that pD-4 was 994 bp long with a 432 bp open leading frame encoding a 143 residue protein. The NH2-terminal amino acid sequence of the natural DiNCF and the deduced amino acid sequence from the cDNA showed that the mature functional protein was comprised of 112 amino acids. Although the deduced amino acid sequence of this protein did not show overall homology to host-derived NCFs or other known proteins, it contained a similar sequence (Met-Phe-Lys) to the known chemotactic peptides. The possibility of the functional epitope of DiNCF is discussed.

Anti-Dirofilaria immitis IgE: seroepidemiology and seasonal variation in an exposed human population

The seroprevalence of seasonal variation of human anti-Dirofilaria immitis IgE levels were studied in an area where specific IgM and IgG had been previously investigated. An antibody capture ELISA assay was used to detect specific IgE. The IgE seroprevalence observed in the whole population was 12.6%. No specific IgE was detected in atopic individuals or in sera from people suffering other helminthiases. The distribution of the IgE anti-D. immitis seroprevalence by age groups did not show differences. Females had significantly higher levels than males. This isotype of immunoglobulin peaks in July, decreasing sharply in October, and persisting at a level similar to that of a non exposed population during the rest of the year. No specific IgE were detected in subjects with pulmonary alterations related to the parasite, suggesting a possible relationship between the clinico-radiological status and the type of immunoglobulin synthesized in subjects infected by D. immitis.

Immunohistological observations on pulmonary tissues from dogs infected with Dirofilaria immitis

Pulmonary tissues from non-infected dogs, naturally Dirofilaria immitis-infected dogs and experimentally infected puppies, selectively necropsied after infection, were assessed using peroxidase-antiperoxidase (PAP) staining technology. Sequential sections of pulmonary tissue were PAP stained with anti-fresh D. immitis serum, anti-paraffin processed D. immitis serum, anti-dog immunoglobulin (IgG, IgG Fc, IgM) sera and anti-dog complement (C3) serum, and examined for antibody, complement and for D. immitis antigen. The extent of alveolar septal thickening was positively correlated with infection status. Cellular infiltration was most evident surrounding obstructed areas where D. immitis were in situ. Antigenic material (microfilariae, eggs, fragmented filariae) labelled by PAP was identified in the pulmonary arteries, alveolar capillaries and alveolar septa. Deposits of complement and IgG, presumably associated with immune complex formation, were also observed in some of the infected dogs. Identification of antigen, antibodies and complement associated with alveolar septal pathology suggested that immune mechanisms were active in its development.

The effect of ketoconazole on pulmonary pathology associated with dead Dirofilaria immitis

The involvement of thromboxane and lipoxygenase in the regulation of pulmonary lesions and immune responses was investigated in dogs given ketoconazole and exposed to dead adult Dirofiliara immitis. Immunopathological reactions to the dead filariae were monitored by light and transmission electron microscopy and serology. When compared with control tissues, ketoconazole administration enhanced the level of pulmonary haemorrhage and early parenchymal fibrosis associated with dead adult filariae. Ultrastructurally, alveolar capillaries were filled with erythrocyte aggregations and proteinaceous material. These results suggested that an intact thromboxane and lipoxygenase pathway within the arachidonic acid system is necessary to minimize the effect of dead D. immitis in this pulmonary artery model.

Immunoglobulin E recognition of Dirofilaria immitis antigens is more specific than immunoglobulin G

The chronological development of the serum IgE and IgG response to microfilaria, third and fourth stage larvae, and male and female adult Dirofilaria immitis was examined by enzyme-linked immunosorbent assay (ELISA) and enzyme-linked immunoelectrotransfer blot (EITB). Dirofilaria immitis-specific IgE and IgG levels peaked 16-18 weeks post-infection after increasing in response to the fourth larval molt. Specific IgG levels plateaued after patency, while IgE continued to decline. The use of ammonium sulfate cut sera showed there was no quenching or blocking of IgE binding by IgG in the ELISA and EITB methods used in this study. IgE-specific EITB showed 30-49 bands for the five respective extracts that were identified by M(r) or relative mobility. Eighty-five to 100 bands were visualized by IgG-specific EITB for the same five extracts. The isotype-specific ELISA and EITB were shown to be closely related by significant correlations (P < 0.0001) between S/N ratios and the number of bands found on blots. The isotype-specific EITB bands non-specifically recognized were greater in size than 21 kDa for IgG and 45 kDa for IgE. Recognition of bands changed over time with some bands being recognized only by prepatent sera. Ten antigen bands of seven M(r) were consistently and specifically recognized by IgE in the five-stage extracts by sera from prepatent and patent infections; only one such M(r) at 13.9 kDa, was described for IgG. A potentially diagnostic 31.9 kDa antigen band was identified on the IgE-specific EITB of D. immitis female extract and was shown to be recognized by IgE in sera from all infected dogs at all time points examined from 2 weeks until 1 year post-inoculation. Overall, IgE reactivity was more specific for D. immitis infections than IgG reactivity.

The humoral response in natural Dirofilaria immitis infections in dogs

Plasma samples from dogs with infections of Dirofilaria immitis were assessed using ELISA and Western blotting techniques. These results were then assessed in relation to age and sex of the host, and to the numbers of microfilariae and adult filariae. Dogs with microfilariae tended to have lower levels of infection. In infected dogs, mean ELISA titres increased directly with the degree of infection. Dogs that were either young or mildly infected, showed a preferential antibody reactivity to antigens in the high molecular weight regions of the immunoblots. With increasing age and/or the extent of infection, an antibody response to antigens in the low molecular weight regions was apparent.

Immunoblot analysis of Dirofilaria immitis recognized by infected humans

To help to develop better diagnostic tests for zoonotic pulmonary dirofilariasis, seven patients with histologically confirmed pulmonary dirofilariasis were evaluated using the immunoblot technique. Six patients exhibited a response to the excretory-secretory (AS) antigen proteins with molecular weights of 20-19.5, 17.5-17 and 14 derived from Dirofilaria immitis adult works. However, when adult worm extracts were used as the antigen, there was no qualitative difference in antigen recognition between the Dirofilaria patients, other patients with non-filarial parasitic infections or with lung cancer or tuberculosis, and normal individuals. All the sera, not only those of the Dirofilaria patients but also those of the non-filarial patients and the controls, strongly cross-reacted with the 18-kDa ES antigen. These findings suggest that the ES antigen of D. immitis provides a more sensitive antigen than does the adult somatic antigen; but the ES antigen and the adult somatic antigen have a common antigenic band at 18 kDa.

Passive transfer of protective immunity to larval Dirofilaria immitis from dogs to BALB/c mice

Protective immunity to larval Dirofilaria immitis has been demonstrated in both the natural host, the dog, and in an experimental host, the mouse. In the present study, sera were collected and pooled from dogs that had been shown to have protective immunity to larval D. immitis. The pooled serum was inoculated into normal BALB/cByJ mice that then were challenged with third-stage larvae (L3) implanted in diffusion chambers. Two weeks postchallenge no significant difference was seen in either parasite survival or growth. Three weeks postchallenge, there was a significant decrease in parasite survival in mice receiving serum from immune dogs. Living larvae recovered at 3 wk postchallenge were significantly shorter than cohorts recovered from control mice. Antibody responses to L3 and forth-stage larvae (L4) surface antigens, to L3 and L4 aqueous soluble antigens, and to an excretory-secretory antigen fraction were measured. Only antibody responses to L3 surface antigens were elevated in the immune serum as compared to controls, thus suggesting a possible role for antibodies with specificity for surface antigens in protective immunity.

Histopathological and immunopathological evaluation of filarial glomerulonephritis in Dirofilaria immitis infected dogs

Filarial glomerulonephritis was studied using Dirofilaria immitis infected dogs. Of 34 infected dogs examined, 15 dogs (44.1%) had histopathological lesions in the kidney. These lesions included an increased number of mesangial cells and increased thickness of the matrix, the infiltration of the small round and plasma cells into the interstitium and thickening of the basement membrane. Deposits of IgG were demonstrated in the infected dogs, whereas C3 deposits were found in all dogs. Combined immunoglobulin and complement deposits were not always found in the dogs with histopathological lesions. The mean concentration (expressed as absorbance) of circulating immune complexes (CIC) was 0.675 +/- 0.517 in infected dogs, and 0.132 +/- 0.092 in uninfected dogs. Although there was significant difference in the level of CIC between infected and uninfected dogs (P less than 0.001), 11 dogs (32.4%) in infected group were negative. Otherwise, the CIC levels were correlated to the adult worm burden (r = 0.848; P less than 0.001) but not to the number of circulating microfilariae (mf) (r = 0.398; P less than 0.05). Transfer of mf to 7 naive dogs was performed to clarify the role of mf in the pathogenesis of filariasis. Antibodies to crude mf antigen became detectable two weeks after the transfer. Neither pathologic findings nor deposits of IgG and C3 in the kidney were found in dogs examined 20 days or 70 days after transfer. There was no evidence that histopathological lesions were induced by live mf, suggesting that adult worm burdens may be more closely related to filarial nephropathy.

Genetic control of murine immune responses to larval Dirofilaria immitis

Previous studies have demonstrated that BALB/c mice, immunized against infection with Dirofilaria immitis, were capable of killing a significant percentage of challenge larvae found within diffusion chambers. The percentage of larvae killed by immunized mice was, however, less than in immunized dogs and unlike immunized dogs, mice were unable to retard the development of the surviving larvae. The objective of the present study was to test 3 inbred strains of mice to determine whether a higher level of protective immunity would develop in these hosts and if larval growth retardation would occur. DBA/2J and C57BL/6J mice and their F1 hybrids B6D2F1/J were used in these studies; it was determined that there were differences in susceptibility among the 3 strains but no difference in ability to eliminate larvae from challenge infections. Growth retardation was seen in larvae recovered from immunized DBA/2J and C57BL/6J mice but not in B6D2F1/J. No difference was noted between immune and control mice in the cell types found in the diffusion chambers. The predominant cell types seen were mononuclear macrophages, multinucleate syncytial cells, and neutrophils. Antibody responses to soluble third- and fourth-stage larval antigens and larval excretory/secretory antigens were measured. Although antibodies to all 3 antigen groups were found in higher concentrations in immunized mice than in their respective controls, only antibody responses to soluble L-3 antigens provided a clear correlation with protective immunity.

[Serology of human dirofilariasis]

The development of an immunoenzymatic technique for the detection of specific IgG against Dirofilaria immitis in humans is reported. Two groups of rabbits were used as controls; one of them was hyperimmunized with D. immitis antigens and the other was not inoculated. Subsequently, the reactivity to D. immitis and T. canis of the sera of three patients with pulmonary nodules and 25 apparently healthy individuals was evaluated. In two of the patients with pulmonary nodules the reactivity against D. immitis was significantly higher than that of healthy individuals. Reactivity against T. canis was not found in any case. These initial results seem to indicate that, in the reported conditions, this technique could prevent crossed reactions between D. immitis and T. canis and could help in the differential diagnosis of other causes of pulmonary nodules.

Influence of immunosuppressants against Dirofilaria immitis infection in dogs

Two immunosuppressive drugs, azathiopurine (AZP) and prednisolone (PDS), were examined on dogs experimentally infected with Dirofilaria immitis in order to estimate the involvement of immunological assail in rejecting the parasite by the host. AZP was orally administered to 3 dogs daily at a dosage of 1-10 mg/kg for a period from 3 days before infection until the end of the experiment. The dose was then varied and transiently ceased according to the severity of the side effects. PDS was subcutaneously administered daily to 2 dogs. They were administered 10 mg/kg of PDS from 3 days before infection to day 15 and 5.0-8.5 mg/kg from day 60 after infection to day 70. The serum D. immitis-specific antibody level assessed by an indirect hemagglutination test was steadily decreased in the AZP-medicated dogs. However, in the PDS-medicated dogs, the antibody titer was decreased until day 32 and, thereafter, was recovered. When all dogs were sacrificed between days 145-148, an average recovery rate of worms in both the AZP- and PDS-medicated dogs was 52.5% and 49.6%, respectively, while the controls showed 42.5%. The statistical analysis revealed no significant difference among the groups, indicating that the administration of AZP and PDS was not effective in protecting the larvae from the host's immune attack.

Experimental Dirofilaria immitis-associated glomerulonephritis induced in part by in situ formation of immune complexes in the glomerular capillary wall

Eight dogs were immunized with an aqueous-soluble extract of adult Dirofilaria immitis. Subsequent to at least 7-fold increases in antibody titer, the left renal artery of each dog was infused with 6 mg of D. immitis antigen. Fourteen days after infusion, the left kidney was compared to the right kidney and preinfusion biopsies. All dogs developed glomerular lesions in the left kidney characterized by 1 or more of the following: mesangial cell proliferation, neutrophil infiltration, increased periodic acid-Schiff-positive staining of the mesangium and glomerular basement membrane (GBM), fibrin deposition, and thickening of the GBM. Left kidney glomerular immunofluorescence was positive in 7 of the 8 dogs using polyclonal antisera for canine IgG and C3 in a linear or fine granular pattern. Ultrastructural lesions were present in the left kidney of all dogs and consisted of irregular GBM thickening, intramembranous and mesangial electron-dense deposits, and mesangial and endothelial cell proliferation. Antibodies directed against D. immitis antigen were demonstrated in all kidney eluates from the left kidney. The right kidneys of 3 of the dogs developed lesions; however, in comparison to the left kidney, the lesions in the right kidneys were inconsistent, mild, and focal. The histologic findings in the left kidney were similar to those observed in dogs with naturally occurring D. immitis infections. In sham-immunized control dogs, renal arterial infusion of D. immitis antigen did not cause consistent immune complex glomerulonephritis; however, antigen adherence to glomerular capillary walls was observed by immunofluorescent microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of immune treatments against Dirofilaria immitis infection in dogs

Mongrel dogs were inoculated with two kinds of antigenic substances. The first was a phosphate buffered saline extract of whole Dirofilaria immitis mixed with aluminum hydroxide gel (group 1), and the second was an orally administered live Metastrongylus apri infective larvae (L3) (group 2). Both groups were then infected with D. immitis L3. Indirect hemagglutination (IHA) tests showed that the antibody was produced by these inoculations before the infection was introduced, even in dogs inoculated with M. apri. This suggests a cross-reactivity between D. immitis and M. apri. The initial passive cutaneous anaphylaxis (PCA) antibody production was markedly delayed by about 70 days in group 2 compared with the production in the infected control dogs (group 3). The appearance of microfilaremia was also delayed by about one month in group 2 compared with that in the above control group. All dogs were sacrificed after the termination of the observation and worms recovered from the right ventricle and pulmonary arteries were counted and measured. The results indicated that immunization resulting from the homologous worm-somatic antigen might accelerate the growth of the infected larvae, whereas immunization resulting from the heterologous worm antigen, but cross-reactive to D. immitis, might disadvantageously affect the growth.

Dirofilaria immitis: studies on anti-microfilarial immunity in Lewis rats

The effect of vaccination on rates of microfilarial clearance using Dirofilaria immitis in male Lewis rats was examined. Animals were immunized with whole, dead microfilariae or a PBS extract of microfilariae in Freund's adjuvant. The immunized animals, as well as untreated and adjuvant controls, were challenged intravenously with 4 x 10(5) viable microfilariae (mf). The duration of microfilaremia was 15.5 days in rats vaccinated with whole mf, 17.7 days in those vaccinated with a PBS extract, 36.3 days for those vaccinated with adjuvant alone, and greater than 70 days for the untreated group. Analysis of the anti-microfilarial IgG response by ELISA and Western blots demonstrated that immunization induced significant amounts of antibody against high molecular weight peptides, particularly a peptide located at 105 kDa. Antibody levels in both groups of immunized animals continued to rise following challenge, reaching peak levels of 78-80 micrograms/ml on the day of microfilarial clearance. Decreasing microfilaremia following challenge was associated with an enhanced recognition of low molecular weight peptides.

A rapid detection of circulating antigens of Dirofilaria immitis in dogs by a dot enzyme-linked immunosorbent assay

This report describes a dot enzyme-linked immunosorbent assay (Dot-ELISA) for detecting circulating antigens in the sera of dogs infected with Dirofilaria immitis (D. immitis). Circulating D. immitis antigens could be detected in 24 of 25 infected dogs. The remaining animal had two immature worms. However, non-infected dogs and dogs infected with other parasites were all negative. Few cross-reactions to different parasite antigens were observed. The advantages of the Dot-ELISA include; 1) there is no need for pretreatment and dilution of sera and samples could be immediately bound to nitrocellulose paper set into microfiltration apparatus, 2) this assay could be carried out within 2 h at room temperature, 3) the resulting enzyme-reaction could be measured by both visual observation and densitometric reading.