[Pulmonary dirofilariasis]

A 70-year-old man was admitted to our department for pulmonary nodule of 15 mm in diameter in the left lower lobe detected by chest computed tomography (CT). A possibility of malignant tumor could not be ruled out, and lung partial resection was performed. Pathological examination during operation revealed a coagulation necrosis and the lesion was finally diagnosed as pulmonary dirofilariasis.

Kidney ultrastructural lesions in dogs experimentally infected with Dirofilaria immitis (Leidy, 1856)

Kidneys of 16 beagles with experimentally induced heartworm (Dirofilaria immitis) infections and 4 heartworm-nai;ve dogs were studied by light and electron microscopy. The infections were induced either by subcutaneous injection of infective larvae or by the transplantation of adult parasites, and infection periods varied from 111 to 818 days and 365 to 923 days, respectively. One control group of heartworm-naïve dogs and four groups of heartworm-infected dogs, which were divided according to the type and the length of infection, were used. In the infected dogs, thickening of the glomerular basement membrane (GBM), the presence of dense deposits in the GBM, and foot process effacement were the most frequent lesions observed. In some dogs, electron dense deposits were seen in the GBM and the mesangium and/or enlargement of the mesangial matrix could be characterized. The longer the infection period, the thicker the GBM and the more common the occurrence of foot process effacement. In general, these alterations were more evident in animals that had been infected for more than 1 year, had high microfilaremia, and had 14 or more parasites in the main pulmonary artery and its branches. The presence of dense deposits suggests that the pathogenesis of kidney disease in dirofilariasis is associated with deposits of immune complexes in the membrane. The finding of ultrastructural changes in dogs with early prepatent infections suggests that immature heartworms, as well as microfilariae and possibly adult worms, contribute to the glomerulonephropathy.

Dirofilaria immitis: further characterization of the transglutaminase enzyme and its role in larval molting

We recently reported the cDNA cloning and functional characterization of a novel transglutaminase (TGase) from the dog filarial parasite Dirofilaria immitis. D. immitis TGase (DiTG) has no sequence similarity with any other known TGase, but has significant similarity to protein disulfide isomerase (PDI)-related endoplasmic reticulum protein ERp60. In the present study. we further characterized the recombinant DiTG (rDiTG) and studied its role in the molting process of third-stage larvae. The enzymatic activity of rDiTG requires Ca2+, and the maximum activity was observed at a calcium concentration of 4 mM. Interestingly, the rDiTG was highly thermostable, with optimal activity observed at 55 degrees C, similar to that seen with the native enzyme. Dithiothreitol (DTT) was not essential for enzyme activity. In fact, rDiTG was more active in the absence of DTT. The known inhibitors of TGase, such as monodansylcadaverine (MDC), cystamine and iodoacetamide, inhibited the TGase activity, but not the PDI activity, of rDiTG, demonstrating the dual activity of rDiTG. The TGase-specific pseudosubstrate, MDC, completely inhibited the molting of D. immitis L3 to L4 if present during the first 24-48 h of the molting process. Electron microscopic studies revealed that MDC-treated infective larvae failed to show separation between the L3 and L4 cuticles. The L4 cuticle and accompanying hypodermis were much thinner in MDC-treated worms than in controls. Using anti-rDiTG antiserum, the native DiTG antigen was localized in the hypodermis, afibrillar muscle cells and gut epithelium in adult male and female worms as well as developing embryos in the females.

Does fertilization in the filarial nematode Dirofilaria immitis occur through endocytosis of spermatozoa?

Information on the ultrastructural details of fertilization in filarial nematodes are still unavailable. Here we report new data on this process in Dirofilaria immits, the heartworm of dogs and cats. Electron microscopy allowed us to observe oocytes engulfing spermatozoa through an endocytosis-like process. We also observed spermatozoa inside the oocytes which still possessed their plasma membrane and which were clearly enveloped by a further membrane, likely derived from the endocytosis process. At this stage, at the interface between the sperm membrane and the endocytotic membrane (vacuolar space), we observed flocculent material in the proximity of the membranous organelles (MOs) of the sperm. In the proximity of the MOs, we also observed the enlargement of the vacuolar space. Other images showed the dissolution of the sperm membrane, and the release of nuclear masses and organelles in the egg cytoplasm. We did not observe the fusion of lysosomes to the endocytotic vacuoles. In addition, the lysis of the sperm organelles has never been observed inside the vacuoles containing the whole sperm. Thus we suggest that the degradation of the endocytotic and sperm plasma membranes is determined by material released by the MOs. Since we did not observe the entry of sperm into the oocytes by other mechanisms, we also suggest that endocytosis is the normal process used by the spermatozoon to get into the egg cytoplasm in D. immitis. Finally, during our observations of the seminal receptacle we did not observe any structure in the spermatozoa which could be interpreted as an intracellular bacterium. This is consistent with previous results indicating that the bacterium Wolbachia in filarial nematodes is not transmitted through the sperm.

Immunofluorescent localization of intermediate filaments (IFs) in helminths using anti-mammalian IFs monoclonal antibody

Intermediate filaments (IFs) make up the cytoskeleton of most eukaryotic cells. In vertebrates, a number of IF proteins have been identified, showing distributions unique to tissue or cell type. Information on helminth IFs is limited to some nematode species. To observe immunofluorescent localization of IFs in helminth tissues, we selected a murine hybridoma clone producing IgM antibody to multiple types of mammalian IF proteins and examined cross-reactivity to helminth proteins. The selected monoclonal antibody (HUSM-9) cross-reacted well with IFs from nematode species such as Toxocara canis, Dirofilaria immitis, Anisakis simplex, and Trichinella britovi; strong immunofluorescence on cryostat sections was detected in the hypodermis, cords, body muscle, smooth muscle of the uterus, and other epithelial structures. In platyhelminths, i.e., adult Schistosoma mansoni, larval Taenia taeniaeformis, adult Taenia crassiceps, and Echinococcus multilocularis protoscolex, the reactivity was weaker than in nematodes, and localized in the body wall muscle and subtegumental tissue. Western blotting of 8 M urea extracts of parasites with the antibody detected a pair of clear bands in nematodes but not in S. mansoni or the cestodes. These results might be explained by sparse distribution of IFs in platyhelminths, or low affinity of the used antibody to platyhelminth IF proteins, or both.

On the rugose area and caudal papillae distribution in Dirofilaria immitis (Leidy, 1856) Railliet & Henry, 1911, by scanning electron microscopy

The objective of this study was to obtain a better characterization of Dirofilaria immitis (Leidy, 1856) Railliet & Henry, 1911, in Brazil, ratifying previous accounts and adding new data on the rugose area on the ventral surface of the spiralled posterior portion of males observed by scanning electron microscopy, which presents a different arrangement compared to other species of the genus, and differs also from the genera Litomosoides Chandler, 1931, and Wuchereria Silva Araújo, 1877, adding another taxonomic character to Dirofilariinae and Onchocercinae. Scanning electron microscopy studies also showed some aspects of the distribution of caudal papillae in D. immitis that have not been described before.

Dirofilaria immitis: ultrastructural localization, molecular characterization, and analysis of the expression of p27, a small heat shock protein homolog of nematodes

A cDNA fragment encoding the complete coding region of a 27-kDa protein (p27) of Dirofilaria immitis was cloned. Antibody to the recombinant p27 bound to hypodermal tissues of third (L3) and fourth stage larvae (L4) of D. immitis and to both the hypodermis and the cuticle of L3s of Onchocerca volvulus, as visualized by immunoelectronmicroscopy. The deduced amino acid sequence of the central and C-terminal regions of p27 (amino acids S83 to H222) is 18-36% identical to members of the sHsp/alpha-crystallin family of proteins. The homologous region is thought to be responsible for the molecular chaperone activity of members of this family. The p27 cDNA does not encode a hydrophobic signal peptide. At least two homologous yet distinct p27 genes were identified in the D. immitis genome by Southern hybridization using the p27 cDNA as a probe. The p27 transcript was 0.9 kb in length on Northern blots. The expression of p27 in L3s of D. immitis was neither upregulated by heat shock (43 degrees C) nor by incubation at the physiologic temperature of 37 degrees C. Pulse-labeling experiments of both D. immitis and Brugia malayi L3s during the L3-L4 molt in vitro showed that synthesis of p27 is also not upregulated during this developmental phase. However, p27 is expressed constitutively throughout the D. immitis L3-L4 molt and therefore by both larval stages. In addition, both female and male adult worms of this species express p27 constitutively. P27, or an allomorph thereof, was detected in each of nine species representing four nematode superfamilies, thus indicating that this molecule is ubiquitous within the phylum Nematoda. In view of the hypodermal localization of p27, its constitutive expression, and its retention among nematodes, the function of this protein in essential housekeeping roles such as that of molecular chaperone during the molting process is discussed.

Mechanism of increased dissemination of chikungunya virus in Aedes albopictus mosquitoes concurrently ingesting microfilariae of Dirofilaria immitis

We investigated whether concurrent ingestion of chikungunya virus and microfilariae of Dirofilaria immitis increases viral dissemination and multiplication in a mosquito vector. The increased rate of dissemination of this virus in mosquitoes concurrently ingesting both agents was found when homogenates of bodies and those of legs only were examined. It was significantly higher than that of controls ingesting the virus alone through the end of the experiment on day 14 after infection. We next studied the mechanism by which the presence of microfilariae enabled the virus to enter into the hemocoel and to reach the salivary glands. We checked our results using histopathologic procedures and electron microscopy by identifying holes produced by the microfilariae that penetrated the midgut epithelial layer. When the midgut of mosquitoes was punctured with a thin needle immediately after the mosquitoes ingested viruses, higher infection rates were observed than in mosquitoes without such punctures.

Dirofilaria immitis: effect of fluoromethyl ketone cysteine protease inhibitors on the third- to fourth-stage molt

D. immitis third-stage larvae (L3) were cultured with fluoromethyl ketone cysteine protease inhibitors. By Day 5 in culture, none of the larvae cultured with 0.1, 0.2, 0.6, or 1.0 mM benzyloxycarbonyl-Phe-Ala-CH2F (Z-Phe-Ala-CH2F) has molted, while 63.2% of larvae in media without inhibitor had molted. At the two lower concentrations of inhibitor more larvae had initiated, but not completed, the molt. In addition to Z-Phe-Ala-CH2F, four other fluoromethyl ketone derivatives, Z-Phe-Arg-CH2F, amorpholine urea-(Mu)-Leu-Phe-CH2F, Mu-Tyr-Phe-CH2F, and Mu-Phe-Phe-CH2F, were tested to determine their effects on L3 in culture. All fluoromethyl ketones tested except Z-Phe-Arg-CH2F inhibited molting. Larvae cultured in inhibitors were determined to be alive as judged qualitatively by motility and quantitatively by reduction of 3-(4,5-diethylthiazol-2-yl)-2,5-diphenyltetrazolium. Electron microscopy demonstrated that L3 which were unable to molt after being cultured in a fluoromethyl ketone derivative had synthesized the new fourth-stage (L4) cuticle but had not shed the L3 cuticle. The same fluoromethyl ketone derivative that did not inhibit molting, Z-Phe-Arg-CH2F, was a slightly less effective inhibitor of larval extract-initiated hydrolysis of the synthetic peptide substrate, Z-Val-Leu-Arg-7-amino-4-methyl coumarin. L3 were also cultured through the molt in media containing the synthetic peptide substrate Z-Val-Leu-Arg-4- methoxy-B-naphthylamide to examine cysteine protease activity in situ. Fluorescence as seen on Days 0-4 during the molting process was first observed on the anterior tip of the larvae, and subsequently in the pharynx, with progression down the L4 as it shed the L3 cuticle.

Determination of the role of cuticular carbohydrates in the hemocompatibility of Dirofilaria immitis (Nematoda)

We have partially characterized surface glycoproteins of the canine heartworm, Dirofilaria immitis. Histochemical studies indicated the presence of neutral and acidic mucopolysaccharides at the blood-cuticle interface. Fluorescein isothiocyanate-conjugated lectin binding patterns suggested the presence of alpha-D-glucosyl and/or alpha-D-mannosyl, beta-galactosyl, N-acetylneuraminyl and N-acetylated-D-hexosaminyl (sialic and glucuronic acids, respectively) terminal residues among the constituent sugars of the glycocalyx. An additional goal of this study was to assess the significance of each carbohydrate in parasite hemocompatibility by using scanning electron microscopy, internal reflection infrared spectroscopy, and comprehensive contact angle measurements. Each carbohydrate identified in the glycocalyx was selectively cleaved with the appropriate exoglycosidase. Heart-worms bearing native and enzyme-altered surfaces were exposed to platelet-rich canine plasma. Activation and aggregation of platelets were significantly increased on enzyme-treated surfaces as compared with native surfaces. Enzyme-induced cleavage of carbohydrate residues was associated with an increase in critical surface tension or a loss in cuticular structural integrity or both. Hemocompatibility of the heartworm cuticle depends on the retention of a stable saccharide-rich layer that minimizes interaction with plasma proteins and platelets; thus, carbohydrate residues on the glycocalyx may contribute to parasite hemocompatibility. The presence of similar low-critical-surface-tension coatings with high mechanical integrity may impart thromboresistance to other polyphenolic or chitinous substances.

Cloning of a cuticular antigen that contains multiple tandem repeats from the filarial parasite Dirofilaria immitis

An unusual antigen composed of tandemly repeated protein units was cloned from the filarial parasite Dirofilaria immitis. The antigen was initially identified by screening a lambda gt11 cDNA library with serum from dogs immunized with irradiated D. immitis third-stage larvae. DNA sequence analysis of the cDNA clone, Di5, revealed a continuous open reading frame composed of two 399-base-pair repeats arranged in tandem. Southern blot analysis of genomic D. immitis DNA showed that the gene coding for Di5 is composed of a tandem array of 25-50 copies of this same 399-base-pair repeat. Antiserum raised against recombinant Di5 protein detected a protein "ladder," from about 14 to greater than 200 kDa with steps approximately 15 kDa apart, on immunoblots of D. immitis extract. Metabolic labeling of adult parasites with [35S]methionine showed that Di5 is synthesized as a large precursor that is subsequently cleaved to produce the ladder-like array. These results suggest that the characteristic ladder is created by proteolytic cleavage of the precursor at the same site in each monomer. The Di5 antigen was localized to the cuticle and hypodermis of adult D. immitis by immunoelectron microscopy. Both male and female parasites were found to release Di5 when cultured in vitro. DNA hybridization analysis demonstrated that Di5 is a member of a gene family present in many filarial parasites that infect both animal and human populations.

Ultrastructural localization of Dirofilaria immitis antigen in canine lung tissue using the protein A-gold labelling technique

Dirofilaria immitis antigens were demonstrated in the pulmonary tissues of dogs, with natural and experimental infection (D. immitis) in dogs using an immunostaining colloidal gold technique. Electron microscopy of thin sections treated with anti-heartworm serum revealed antigen deposition within the pulmonary microvasculatur and perivascular areas.

Dirofilaria immitis: molting process of third-stage larvae

The objective of this study was to determine the molting process of Dirofilaria immitis third-stage larvae (L-3) to fourth-stage larvae (L-4), as it occurred in vitro. After 48 hr in vitro, the L-4 epicuticle was completely formed, and by 72 hr there was a clear separation between the L-3 and L-4 cuticles. The thickness of the newly formed L-4 cuticle was significantly less than that which has been described for larvae recovered from dogs after a similar incubation time period. If culture conditions were lacking in bovine albumin or proper temperature, larvae successfully developed the L-4 epicuticle but did not complete ecdysis. The molting process of D. immitis L-3 was thus shown to be multistepped with different factors required to induce the various developmental phases.

Surface characterization of the cuticle of Dirofilaria immitis

The surface reactivity of the dog heartworm (D. immitis) was evaluated by comprehensive contact angle measurements and a platelet retention test. Contact angle data yielded calculated surface energy terms very similar to those previously reported for intact vascular endothelium. The platelet test revealed the native worm surface to be nonreactive, retaining fewer platelets than glass or worms whose surfaces had been modified by extraction with acid and high salt solutions. The cuticular morphology of the heartworm was studied with both light and electron microscopy, the latter coupled with ferritin-conjugated double-layer immunolabeling to reveal adsorbed host protein on the cuticle surfaces. Multiple attenuated internal reflection (MAIR) IR spectroscopy confirmed the general composition of this surface layer to be glycoproteinaceous. Morphological and histochemical studies confirmed and extended previous descriptions of nematode cuticle, adding ultrastructural detail on cortical, medial, and basal layers. A trilaminar membrane, apparently corresponding to a mammalian cell membrane (plasmalemma), constituted the external cortical layer as observed in high magnifications. The existence of a glycocalyx of varying thickness was demonstrated in ruthenium red-stained sections. MAIR IR spectra showed this glycoproteinaceous film to appear, in fully hydrated samples, as a loose biological gel. Ferritin-antibody conjugate labeling confirmed the presence of adsorbed dog albumin, dog immunoglobulin class G (IgG) and dog complement fraction 3 (C3) in the cuticular surface layer. It is likely, therefore, that D. immitis heartworms demonstrate long-term thromboresistance at least in part due to their passive low-surface-energy overcoating with host proteins.

Partial characterization of the adsorbed protein layer on Dirofilaria immitis (Nematoda) cuticle

Electron microscopy coupled with ferritin-conjugated indirect immunolabeling was used to locate sites of adsorbed host protein on cuticular surfaces of the adult canine heartworm, Dirofilaria immitis. The epicuticle appeared as a trilaminated structure. At high magnifications, the outermost layer of this structure was resolved into a trilaminar layer, which might correspond to the plasma membrane of animal cells. A ruthenium red-positive layer was external to the epicuticle. Ferritin-antibody conjugates showed evidence of adsorbed dog albumin, dog immunoglobulin class G (IgG), and dog complement fraction 3 (C3) on the surface. Ferritin adsorption to control surfaces was minimal. Possible causes and effects of interfacial host-protein adsorption are discussed in an attempt to bring insight to the hemocompatible nature of the parasitic cuticle.

Solubilization of epicuticular antigen from Dirofilaria immitis third-stage larvae

The solubilization of epicuticle from third-stage (L3) Dirofilaria immitis larval cuticles was investigated. Cuticles collected after L3 had molted were incubated in 1.5% sodium dodecyl sulfate (SDS) at 37 degrees C with vigorous shaking. Solubilization of epicuticular layers was accomplished as demonstrated by electron microscopy. Diminished binding of an epicuticular specific monoclonal antibody (DIM-229) was seen when SDS-treated cuticles were compared to untreated cuticles in an indirect fluorescence antibody assay. Cuticles which were extracted further by boiling in 1.5% dithiothreitol (DTT) produced less protein than cuticles solubilized in SDS. Both extracts reacted with DIM-229 in an indirect enzyme-linked immunosorbent assay, indicating retention of antigenic reactivity of the solubilized epitope. SDS-polyacrylamide gel electrophoresis of SDS-derived antigens revealed, after silver staining, proteins from 12 to 77 kDa and only 1 band at 15 kDa for SDS-treated cuticles boiled in DTT. Western blot analyses of the extracts with DIM-229 were inconclusive.

Dirofilaria immitis: surface properties of third- and fourth-stage larvae

The objective of this study was to analyze surface properties of larval Dirofilaria immitis with potential relevance to protective immunity. Comparisons were made between third (L3)- and fourth-stage larvae (L4) based on their net surface charge, surface carbohydrate and antigen composition, ability to nonspecifically absorb host proteins, complement activation, and nonspecific cellular adherence. It was determined that L3 had a net negative surface charge, whereas L4 had either a neutral or weakly positive surface charge. The lectin Con A, but not any of the other lectins tested, bound only to the surface of L4, and not to that of L3. Monoclonal antibodies were prepared which reacted with the surface of L3 or with the surface of L4, but never both. L4 were found to nonspecifically adsorb host protein to their surfaces, whereas L3 did not. Both L3 and L4 were found to activate complement through the alternate pathway. Finally, nonspecific cellular adherence was found on L3 both in vitro and in vivo but not on L4. The surfaces of L3 and L4 were thus shown to be significantly different and, potentially, in ways which would have great impact in the generation and effectiveness of a protective immune response.

An ultrastructural study of Dirofilaria immitis infection in the Malpighian tubules of Anopheles quadrimaculatus

An ultrastructural study was conducted of the Malpighian tubules of Anopheles quadrimaculatus, both uninfected and following infection with Dirofilaria immitis. The Malpighian tubules in Anopheles are composed of primary and stellate cells. The primary cells are the predominant cell type and are characterized by the presence of membrane-bound, intracellular, mineralized concretions and large apical microvilli containing mitochondria. Following the infective blood meal, the microfilariae enter the primary cells of the Malpighian tubules and reside in the cytoplasm in a clear zone without a delimiting membrane. Cells in infected tubules differ from those in uninfected tubules in that the membranes of the vacuoles surrounding the concretions are disrupted in many specimens. The apical and basal cell membranes and the mitochondria associated with these are not disrupted during the first 6-8 days of infection. These observations differ sharply from those previously described in Aedes taeniorhynchus infected with D. immitis. The observations are consistent with the hypothesis that the extended transport capacity observed in previous physiological studies of An. quadrimaculatus infected with D. immitis are dependent on the prolonged normal ultrastructure of the apical microvilli, mitochondria, and basal membranes.

Hemocyte-mediated melanization of microfilariae in Aedes aegypti

The melanization response of adult female Aedes aegypti (black-eyed Liverpool strain) against intrathoracically inoculated Dirofilaria immitis microfilariae (mff) was assessed with transmission electron microscopy. The initial reaction involved the lysis of hemocytes at or near the surface of the parasite prior to the deposition of pigment. Subsequently, melanin formation was noted in the area of lysed cells and appeared to cascade onto the parasite surface. Observations suggest that melanin may be synthesized within certain hemocytes and released by exocytosis or upon cell lysis. Intact and disrupted nuclei and cytoplasmic elements from lysed hemocytes became numerous as mff became completely coated with melanin. A double membrane-like structure formed around the melanized mff and cellular debris during the later stages of the reaction, which eventually isolated the melanin capsule from hemolymph components. Results obtained are discussed in relation to the melanization response previously described for Aedes trivittatus.

The ability of microfilariae to evade in vitro cell-mediated cytotoxicity

When microfilariae (Mf) of Dirofilaria immitis, both uterine and systemic, were incubated in an in vitro cytotoxicity assay with neutrophils and sera from dogs with occult infections, some Mf remained free of adherent cells and consequently evaded cytotoxicity. The ability to evade cytotoxicity could not be related to the age of the Mf, and host albumin was not detected on any Mf, either uterine or systemic. However, it was shown that some Mf failed to bind IgM, IgG and C3 when incubated with occult sera. It is suggested that the ability of some Mf to evade serum-dependent, neutrophil-mediated cytotoxicity in vitro was related to differences in their antigenicity.

Dirofilaria immitis: the moulting of the infective larva in vitro

A number of in vitro culture systems were tested for their ability to support the development of Dirofilaria immitis infective larvae to the fourth larval stage. In cultures of medium ML-15 containing a feeder layer of Dog Sarcoma (DS) cells larvae successfully moulted and showed a small but significant increase in length. Ultrastructural observations demonstrated that the fourth-stage cuticle was synthesized in vitro and in some larvae was fully formed by 60 hours of culture. The hypodermis of moulting larvae contained numerous multi-vesicular bodies. It is concluded that the moult in vitro is a true moult and not an atypical response of the larvae to the conditions of culture.

Lesions in the liver and kidney of Dirofilaria immitis-infected dogs following treatment with ivermectin

Six dogs with spontaneous heartworm disease were injected with a single dose of ivermectin. After 48 h of treatment, microfilariae counts were reduced by 92%-98% of pretreatment counts. In pretreatment biopsies examined by light and electron microscopy, microfilariae were unaltered in the sinusoids of the liver and also in the glomerular capillaries and interstitial blood vessels of the kidney. However, there was irregular thickening and dense deposits in the basement membranes of glomerular capillaries, along with a modest increase in mesangial cells and matrix. In post-treatment liver biopsies examined by light microscopy, there were numerous granulomas in the sinusoids which contained degenerated microfilariae. In post-treatment kidney biopsies there was moderate thickening of glomerular basement membranes along with pronounced proliferation of mesangial cells and matrix. Glomerular capillaries were partially or completely occluded by degenerated microfilariae. In addition, there were interstitial granulomas in the kidney. It was observed with the aid of electron microscopy that highly vacuolated and degenerated microfilariae were incorporated into granulomas in the liver sinusoids of post-treatment biopsies. In post-treatment kidney biopsies glomerular capillaries were usually occluded by degenerated microfilariae. Basement membranes were thickened and contained dense deposits. Mesangial cells and matrix were extensively increased. Interstitial granulomas in the kidney contained dead microfilariae.

Immunoglobulin interactions with surfaces of sheathed and unsheathed microfilariae

The sheath surface of Brugia pahangi microfilariae (mf) and the cuticle surface of Dirofilaria immitis mf were compared with regard to the ultrastructural arrangement of neutral and charged polysaccharides and binding of immunoglobulins from dog sera. Brugia pahangi: mf demonstrated large amounts of neutral sugar and negatively charged sugars just above the sheath surface, projecting some distance from the surface, in addition to a dense layer of sulphated material on the sheath surface. Microfilariae from high microfilaremic dogs showed no innately bound IgG or IgM when examined fresh from serum nor did they bind IgG or IgM from normal (NDS) or infected (IDS) dog sera after 48 h maintenance in RPMI 1640. Many of these mf did bind IgG and IgM from hyperimmune dog serum (ImDS) and these immunoglobulins were found binding at a distance from the sheath similar to that of the sugars. Dirofilaria immitis mf demonstrated much less neutral sugar at the cuticle surface, no negatively charged sugars and a diffuse, rather than dense, distribution of sulfated material extending from the cuticle. The majority of these mf showed innately bound IgG and IgM. After 48 h maintenance in RPMI 1640 D. immitis mf bound and shed IgG and IgM from NDS, high microfilaremia D. immitis IDS and D. immitis mf ImDS at distinctly different rates.

Immunological and ultrastructural aspects of the cell-mediated killing of Dirofilaria immitis microfilariae

Neutrophils in the presence of serum from dogs with occult Dirofilaria immitis infections were shown to be cytotoxic to D. immitis microfilariae recovered from the blood of microfilaraemic dogs. This cytotoxicity was correlated with the presence of IgM and IgG antibodies on the cuticular surface of microfilariae incubated in the sera from occult dogs. Such antibodies were not observed on the surface of microfilariae incubated in sera from microfilaraemic or normal dogs. The neutrophil attack was directed at the cuticular crypts, at which sites the worms appeared to be structurally most vulnerable because of the absence of the outer layer of the cuticle. The IgM antibodies were shown to be bound preferentially to these sites. Our data suggested that the neutrophil-mediated toxicity involved both hydrogen peroxide release and degranulation.

In vitro immune mechanisms associated with clearance of microfilariae of Dirofilaria immitis

An in vitro system has been developed to elucidate potential immune mechanisms associated with clearance of microfilariae (Mf) from the bloodstream in canine Dirofilaria immitis infection. Granulocytes as well as mononuclear cells adhere to Mf of Dirofilaria immitis in the presence of immune serum. Only granulocytes, however, were capable of killing Mf, whereas PBMC attach to but do not effectively kill Mf. In the presence of granulocytes 1% +/- 1, 10% +/- 2, and 12% +/- 3 of Mf were killed by heated normal (NDS), patent (PS), and occult serum (OS), respectively, after an 18-hr incubation. With the addition of fresh NDS there was an increase in killing to 5% +/- 1 (p less than 0.025) with heat-inactivated NDS, to 12% +/- 3 in the presence of PS and to 77% +/- 12 (p less than 0.005) in the presence of OS. On further purification of granulocyte cell populations with metrizamide gradients, neutrophils were found to be the predominant effector cells with 73% +/- 18 killing with neutrophils and 18% +/- 6 with eosinophils (p less than 0.0005). Only with neutrophils was a significant increase in killing of Mf observed when fresh NDS was added to delta OS. Fractionation of OS by gel filtration suggested that IgM was the opsonizing antibody in the occult serum. In addition, immunofluorescent studies showed only IgM bound to the surface on Mf on incubation in OS. The involvement of complement in the fresh serum enhancement of killing was supported by the finding, by immunofluorescence, of surface C3 on Mf after incubation in fresh OS.

Fate of microfilariae of Dirofilaria immitis following use of levamisole as a microfilaricide

A pretreatment liver biopsy was secured from each of three dogs with Dirofilaria immitis microfilariae counts of 29,500, 24,700, and 76,700/ml blood, respectively. Post-treatment biopsies were obtained 30 h later following treatment with a single dose of levamisole and a reduction in microfilariae counts of up to 80%. Both pre- and posttreatment biopsies were examined by light and electron microscopy. Microfilariae in dilated sinusoids of pretreatment liver biopsies were not degenerated and were unattended by an inflammatory reaction when examined by either method. However, degenerated microfilariae were present within granulomas in post-treatment liver biopsies examined by light and electron microscopy. Several stages of degeneration of microfilariae, including phagocytosis, were identified by the latter method.

Dirofilaria in the abdominal cavity of a man in Japan

A case of human dirofilariasis of the abdominal cavity is reported from Japan. The patient, a 74-year-old man, died of liver cancer; postmortem examination revealed a granulomatous mass on the mesentery. In histologic sections there were cross-sections of a mature female nematode identified as a Dirofilaria. The cuticle had a smooth surface and consisted of four distinct layers. The inner cuticular layer had internal lateral longitudinal ridges, and the musculature of the body wall was of the high polymyarian type. On the basis of morphology of the worm, it is suggested that this may represent the first human case of Dirofilaria immitis occurring in the abdominal cavity.

Cuticular morphology of five species of Dirofilaria: a scanning electron microscope study

Cuticular markings of five species of Dirofilaria were examined by SEM. Variations in the patterns on the en face view were observed among the species. Transverse striations were observed on the cuticles of all five species, but longitudinal ridges were lacking on Dirofilaria immitis, the type species of the subgenus Dirofilaria. They were present on the other four species, Dirofilaria repens, Dirofilaria tenuis, Dirofilaria corynodes, and Dirofilaria magnilarvatum, members of the subgenus Nochtiella. Longitudinal ridges and other cuticular structures and patterns were seen to vary among the species and with the portion and aspect of the worm examined. It is suggested that SEM would be a good tool for a detailed study of specific cuticular morphology of all species of Dirofilaria, thus contributing toward their differentiation and recognition.

Micro-organisms in filarial larvae (Nematoda)

Unusual bodies have been described in the hypodermal tissues of larval Dirofilaria immitis and Brugia pahangi. Ultrastructural evidence indicates that these bodies are probably Gram-negative micro-organisms. It appears that the presence of large numbers of these bodies in an early embryo may affect development adversely. Their importance at later stages of development of filariae is not known.