Vaccine from Dirofilaria extracts

Abstract

A vaccine for protecting animals against infection by Dirofilaria which comprises fractions of extracts of the adult organisms of Dirofilaria.

Description

FIELD OF THE INVENTION

This invention relates to a preparation of an antigenic component for use in a vaccine for the prevention of parasitic disease caused by Dirofilaria. More particularly, it relates to the preparation of antigens which can be used to vaccinate as a preventative against subsequent infection by the disease entity but also may be utilized as a vaccine to inhibit the course of development of the parasite in the early pre-patent stages of the disease cycle of the organism.

BACKGROUND OF THE INVENTION

Dog heartworm (Dirofilaria immitis) is a parasite which principally affects dogs but also has been shown to infect other animals such as cats, foxes, raccoons, ferrets, and even man. Other species of Dirofilaria infect additional hosts. For example, Dirofilaria filaria causes parasitic disease in sheep; D. viviparus causes parasitic disease in cows.

The life cycle of Dirofilaria is instituted through the bite of a mosquito which had previously bitten an infected animal. The infective larvae remain in the mosquito where they undergo three molts, after which the infective larvae migrate to the mosquitos' proboscis. The larvae are then ready to be transmitted to another host. The entire maturation process in the mosquito takes anywhere from 7-14 days.

The infective larvae enter an animal following the bite of a mosquito and then pass through three additional molts after which the adolescent parasites migrate to the heart where they will undergo final maturation. Approximately 25-37 weeks will normally transpire following infection, either as a result of infected mosquitoes biting a host or due to subcutaneous injection of appropriate larvae into animals, before microfilaria can be detected by microscopy in the blood of animals so infected.

There have been numerous attempts to prepare antigenic material as immunizing agents against Dirofilaria (Otto, in G. J. Jackson et al., Eds, Immunity to Parasitic Animals, Appleton-Century-Crofts, N.Y., pp. 963-980, 1970) reviewed attempts up to that time to immunize dogs against D. immitis and reported that the use of material from adult parasites had been unsuccessful.

Hyong-Sun et al. (in Canine Heartworm Disease, The Current Knowledge, Bradley and Pacheco, Eds, U. of Florida, Gainesville, 1972, pp. 55-67) utilized viable microfilaria as a possible vaccine for dog heartworm. They immunized dogs using seven vaccinations of microfilaria at three-day intervals into animals which were subsequently challenged with infectious larvae from laboratory-raised mosquitoes. The vaccinated animals showed microfilaria following challenge about two weeks after the unvaccinated controls and showed fewer microfilaria. However, this vaccination program showed that the viable microfilaria as a vaccine had little if any effect in altering the numbers of adult worms found in the vaccinated groups and the control groups which were not vaccinated.

Hyong-Sun et al. also attempted immunization of dogs with 15 kilorads (Kr) irradiated microfilaria but found that this level of irradiation was not lethal to all of the infectious larvae and, therefore, in the control groups so vaccinated but unchallenged, some of the dogs were ultimately found to have adult worms. The vaccine, therefore, was not effective.

Jovanovic, Acta Veterinaria 33(5-6):315-322 (1983), report attempts to vaccinate sheep against infection by D. filaria.

Sawada et al., Japan J. Expt. Med. 35(2): 125-132 (1965) (Chem. Abstr. 63: 16947), report isolation and purification of an antigen for an intradermal skin test. The antigen is extracted from a D. immitis homogenate with phosphate buffer (pH 7.2) and purified by a series of filtration and chromatographic procedures.

Boto et al., J. Immunol. 133(2): 975-980(1984), report analyses of D. immitis antigens prepared by detergent extraction (pH 7.4) of a D. immitis homogenate.

Maggio, European Patent Application No. (EP-A) 142,345, report published May 22, 1985, disclose use of anti-idiotypic monoclonal antibodies. Included in the disclosure are antibodies raised against a fraction of a D. immitis homogenate which is soluble at pH 3.5.

In Australian Patent Application No. 84-36-095 is disclosed a diagnostic assay employing an antibody raised against a D. immitis extract. The extract is prepared by extraction of an adult D. immitis homogenate with phosphate buffered saline at 4.degree. C. and filtering the supernatant thereof.

Swamy et al., Molec. Biochem. Parasit. 9:1 (1983), report isolated from two acid proteases from adult D. immitis extracts.

Grieve et al., Acta Tropica 42:63 (1985), report antigens which were solubilized from aqueous-insoluble material of adult female D. immitis with a detergent.

SUMMARY OF THE INVENTION

In one aspect, this invention is a vaccine for protecting a mammal from infection by Dirofilaria which comprises an effective, non-toxic amount of a water-soluble fraction and of an acid-soluble fraction of an extract of adult Dirofilaria organisms.

In other aspects, this invention is a process for preparing such vaccine and a method for protecting a mammal from infection by Dirofilaria which comprises internally administering such vaccine to the mammal.

These and other embodiments, which are fully disclosed below, are further aspects of the same invention.

DETAILED DESCRIPTION OF THE INVENTION

Development of a vaccine which constitutes this invention was predicated on the premise that a vaccine should elicit protective antibodies that would be active against the developing parasite prior to the establishment of adult worms and the formation of circulating microfilaria (the pre-patent stage of infection). Since the infectious larvae, as well as the adult worms, have passed through a metamorphosis of development, they contain a plethora of antigenic components, some of which may not elicit detectable and/or protective antibodies and some of which may be repressed as antigenic stimuli unless fractionated out from the multiplicity of antigens of which these intact parasites are composed. The determination as to which antigen(s) would be useful as a vaccine was determined by the fractionation of adult worms in order to discover those antigens which would be representative of antibodies present in the pre-patent stages of the infectious process. Schemes 1 and 2, below, represent procedures utilized to prepare a series of antigenic fractions which, when tested against dog sera from dogs that had been infected at various stages, showed varied activity in detecting circulating antibody. ##STR1##

It was found that the acid-soluble fractions, e.g., 91-90B in Scheme 1, 91-163G.sub.s in Scheme 2, and 91-163H.sub.s in Scheme 2, were more efficacious in detecting antibody in animals during the early stages of infection whereas the water-soluble fraction, e.g., 71-150D in Scheme 1, was most sensitive in detecting antibody during the latter stages of infection.

To stimulate production of protective antibodies over the prolonged period during the prepatent stage that would interfere with the metamorphosis and development of the parasite prior to the onset of the adult worm in the heart and lungs of an infected animal or man, and/or so that a developing parasite would act as an anemnestic antigenic stimulus for enhanced release of antibodies into circulation which would disrupt continued development of Dirofilaria prior to the adult stage, both the acid-soluble and water-soluble fractions were used to prepare the vaccine of the invention as described in the Examples below.

The vaccine of this invention thus comprises two fractions of adult Dirofilaria extract in a pharmaceutically acceptable carrier. One fraction is water-soluble, meaning that it is soluble in aqueous solvent at about neutral pH, for example, pH 6.5-7.5, as evidenced by the solubility of this fraction in phosphate buffered saline (PBS) at about pH 7. The other is acid-soluble, meaning that it is soluble in aqueous solvent at low pH, for example, pH 3-5, as evidenced by the solubility of this fraction in acids such as hydrochloric acid, trichloracetic acid or acetic acid at about pH 3.5-4.8.

Adult Dirofilaria for use in preparing the vaccine of the invention are available from a variety of sources, including infected animals such as canines. A population of such infective larvae can be maintained by allowing mosquitos, for example, Aedes aegypti, to feed on an infected animal. Extracts of Dirofilaria can be prepared by any technique which disrupts the organism and are typically prepared by physical disruption such as grinding. The organisms are preferably washed prior to disruption. Following disruption, one or successive fractions which are soluble in aqueous solution at neutral pH but which are not soluble in aqueous solution at low pH are collected, as are one or successive fractions soluble in aqueous solution at low pH but which are not soluble in aqueous solution at neutral pH. The two fractions are combined in a 10:1 to 1:5 (w/w) water-soluble:acid-soluble ratio, preferably about 4:1 (w/w) water-soluble:acid-soluble. The pH of the vaccine is adjusted such as by addition of base and/or dialysis to prepare a tolerated injectable solution. A preservative such as sodium azide or merthiolate can be added.

The vaccine can be adjuvanted with any adjuvant acceptable for internal administration to the vaccinate. The examples reported below demonstrate that use of a carbohydrate polymer, especially an alginate, as an adjuvant gives an unexpectedly superior immunoprotective response. Alginate is a derivative of alginic acid. Alginic acid is a carbohydrate co-polymer of L-guluronic acid and D-mannuronic acid residues resulting in a polymer structure similar to cellulose. Alginate can be extracted from seaweed. It is also publicly available from other sources, including commercial vendors such as Kelco (Chicago, Ill.). Use of alginate as a vaccine adjuvant is disclosed, for example, by Scherr et al., U.S. Pat. No. 3,075,883; Schechmeister et al., U.S. Pat. No. 3,925,544; and Billiau et al., U.S. Pat. No. 3,839,555. An alginate adjuvant typically comprises 1% to 5% of each vaccine dose.

Other examples of useful carbohydrate polymers are pluronic polyols, L121 & T1501, for example, which are co-polymers of polyoxypropylene and polyoxyethylene. (Hunter et al., J. Immunol:133(6):3167) and polyoxyethylene sorbitan monooleate (Tween 80) and sorbitan monooleate (Span 80) (Woodard et al., Vaccine 3: 137).

The vaccine is formulated by dilution with an acceptable excipient, such as normal saline or buffered aqueous solution, or concentrated, such as by dialysis. Vaccines containing up to 5000 .mu.g/dose of the combined fractions from D. immitis have been tested and shown to be effective. The preferred dose range is about 0.5 to 200 micrograms/dose, especially about 1-75 micrograms of extract per vaccine dose. The vaccine is administered parenterally, by intramuscular, subcutaneous or intradermal administration. The preferred route of administration in dogs is by subcutaneous injection.

Typically, the vaccine will be administered in two doses, the second dose being about 1 to 6 weeks, preferably about 3 weeks after the first. The dose volume is in the range of 0.5 to 3 ml, preferably about 1 ml. Re-vaccinations can be periodically administered, for example, yearly or bi-annually. Preferably, the initial vaccination is administered prior to infection, that is, to young animals 6 to 8 weeks old or to animals which otherwise have not been exposed.

The antigenic components which comprise the vaccine of this invention can be combined with vaccinal amounts, that is, safe and effective amounts, of other Dirofilaria antigens or with other antigens which can induce an immune response to infection by one or more other pathogenic bacteria, parasite, virus or other invasive microorganism, provided that such additional antigenic components do not significantly adversely affect the immune response to the protective Dirofilaria antigens.

The examples which follow are illustrative, but not limiting, of particular embodiments of this invention. All reagents are commonly available. Alginate was obtained from a commercial source (Kelco, Chicago, Ill.); Quil A is a saponin (see, for example, Dalsgaard, Acta Vet. Scand. 18:349-360(1977)) which was purchased from Sepulco (Belletente, Pa.); Montanide 888 is a monooleate which was purchased from Seppic (Paris, France); Polyol 121 was purchased from BASF, Wyandotte, Mich.

EXAMPLES

MATERIALS AND METHODS

A. Source

Mature Dirofilaria immitis were collected from the hearts of dogs and stored frozen at -70.degree. C.

B. Fractionation of D. immitis Vaccine Antigen

Fractionation of adult heartworm antigen was performed as follows:

Twenty grams of adult heartworm were washed three times in phosphate buffered saline (pH 7.3), placed in a mortar and ground for 15 minutes in the presence of 5 g of pumice rubbing compound (Bordex) and 5 ml of PBS. An additional 5 g of pumice and 5 ml of PBS were added and the contents were ground for an additional 10 minutes.

The contents were centrifuged and the supernatant was removed and stored. The residue was ground again in the presence of 10 g of pumice and 15 ml of PBS.

Following centrifugation, the residue was saved and the supernatant was pooled with the supernatant which had been collected following the first centrifugation.

The pooled supernatants were centrifuged at 12,000 rpm for 30 minutes at 5.degree. C. to pellet the remaining pumice and cell debris. The residue was pooled. The pooled supernatants were centrifuged at 20,000 G to clarify and then were stored at -70.degree. C.

The residues collected above were combined and the pH was adjusted to 3.5 with 40 ml of 20% glacial acetic acid.

Ten additional grams of pumice were added and the contents were ground for 5 minutes and stirred overnight at 4.degree. C.

The supernatant was removed and stored. The top part of the residue in the centrifuge tube (the cell debris) was removed, ground briefly, and the pH was adjusted to 3.5 with acetic acid. The pumice left in the tubes was added to the cell debris, the contents were ground for 5 minutes and then were centrifuged at 20,000 G.

The supernatant was removed and was combined with the supernatant which had been collected following the first centrifugation. The supernatants were centrifuged again at 20,000 G, dialyzed again at 0.85% saline (pH 3.5) and then were stored at -70.degree. C. Protein concentration was determined by the Lowry Procedure.

C. Preparation of Vaccines

All vaccines contained a 4:1 ratio of PBS-soluble to acetic-acid soluble D. immitis antigen. The vaccines contained 0.01% merthiolate.

Vaccines were adjuvanted with either alginate, Quil A (Sepulco), Quil A and 50% oil and Montanide 888 (Seppic), or Quil A and 5% oil and polyol L121 (Wyandotte Co.).

D. Vaccination Procedure

Dogs were vaccinated twice either intradermally (ID), subcutaneously (SC), or intramuscularly (IM).

E. Antibody Responses to D. immitis Antigens

Serum of dogs were tested for antibodies to D. immitis by a passive hemagglutination test (PCA). Test and control sera in 25 microliter (ul) volumes were diluted in serial twofold dilutions in U-bottom microtiter plates. With a Pasteur pipette, 35-40 ul of sodium dibasic, potassium monobasic phosphate buffer with 0.5% bovine serum albumin (BSA) was added to each well. One drop from a Pasteur pipette of Dirofilaria immitis-sensitized sheep red blood cells was put in each well and incubated at room temperature overnight (this test can be read after 1 hour). The titer was that dilution of serum which produced visible agglutination.

F. Evaluation of Pathogenicity Pathogenicity of third stage larval (L3) infection was evaluated in two ways: (1) Ten mosquitos that contained L3 in their salivary glands were macerated and injected SC into each dog in Efficacy Test No. 1; 2) infective L3 were first removed from the salivary glands of mosquitos. Twenty-five larvae were then injected subcutaneously (SC) into each dog in Efficacy Test No. 2.

After 220 days post-infection in Efficacy Test No. 1 and after 199 days post-infection in Efficacy Test No. 2, the dogs were euthanized and their hearts and lungs were examined for adult heartworms.

G. Efficacy Studies

Efficacy was determined by vaccination and challenge studies. The vaccination procedure is described in Section D above, and the evaluation of challenge is described in Section F, above. Serum was collected prior to vaccination and following each vaccination.

1. Efficacy Test No. 1

Five mixed breed littermates, 12 weeks of age (A1-A5), and 6 mixed breed littermates, 4 weeks of age (B1-B5 and B7), were vaccinated. One puppy from each litter (A6 and B6) was selected as non-vaccinated non-infected controls. Two additional dogs, C1 and C2, were vaccinated but not challenged. Two dogs, D1F2 and D2F2 were not immunized but were infected.

All dogs were housed in a barn or in outside runs. They were not screened from mosquitos.

The acetic acid soluble antigen was diluted to a concentration of 1.5 mg/ml of protein. The dogs received 0.1 ml intradermally into 3 separate injection sites and 0.2 ml intramuscularly into 3 separate injection sites on 8-13-80.

On the following day each dog was vaccinated with the PBS-soluble fraction at a concentration of 5 mg/ml. The dogs received 0.1 ml intradermally into 3 separate injection sites followed by 0.2 ml injected intramuscularly into each of 3 injection sites.

Twenty-five days later the vaccinated dogs were immunized a second time and in the same manner.

Serum for serological testing and testing for microfilaria was collected periodically. On the 544th day following vaccination all of the surviving dogs that were vaccinated and two non-vaccinated dogs that had been shown to be free of D. immitis were challenged.

Serum for serological testing and testing for microfilaria was collected periodically following challenge.

2. Efficacy Test No. 2

Seventeen mixed breed dogs and 27 beagles, 3 to 6 months of age, were randomly divided into 10 vaccine groups. All dogs were housed in outside pens. Four groups, consisting of 6 or 3 dogs per group, were inoculated with vaccine antigen adjuvanted with different adjuvants two times, about 3 weeks apart. The adjuvants were: (1) 300 micrograms (.mu.g) Quil A; (2) 300 .mu.g Quil A, 45% oil, 5% Montanide 888; (3) 300 .mu.g Quil A, 5% oil, and 5% polyol 121; and (4) 2.5% alginate. Three dogs in each group were inocilated SC and 3 dogs in 3 of the groups were inoculated IM. Four other vaccine groups were inoculated SC with vaccine consisting of either 40, 4, or 0.4 .mu.g/ml of vaccine antigens adjuvanted with 300 .mu.g Quil A, 45% oil, and 5% Montanide 888 or of 40 .mu.g/ml of antigen with 2.5% alginate. An additional 2 groups of 2 dogs each were inoculated SC with vaccine consisting of either 40 or 4 .mu.g/ml of vaccine antigen adjuvanted with 300 .mu.g Quil A, 45% oil, and 5% Montanide 888.

Serum for serological testing was collected before vaccination, 7, 19 and 21 days post first vaccination and 7, 14, 21, 28, and 56 days post second vaccination. Serum for serological testing was collected from dogs that were challenged at 3, 6, 10, 12, 15, 18, and 21 weeks post challenge.

RESULTS

Efficacy Test No. 1

The passive hemeagglutination (PHA) antibody titers of all dogs except B4 and A6 were low following vaccination (Table 1). Dog A6 was a dog that was neither vaccinated nor challenged. Dog B4 was a vaccinated dog. Its titer remained high after challenge.

All vaccinated dogs except A4 were free of heartworm 173 days post challenge. Microfilaria were detected in the blood of DOG A4 prior to challenge. This dog was evidently naturally infected after being vaccinated. Microfilaria were also detected in the blood of dog A6. This dog was neither vaccinated nor challenged. Mature heartworms were collected from both dogs that were not vaccinated but experimentally infected with D. immitis infective larvae.

TABLE 1__________________________________________________________________________Antibody Response of Dog to D. immitis AntigensFollowing Vaccination and ChallengeReciprocal of PHA TiterVaccination Dog Days Post Vaccination Days Post Infection Results of ChallengeInfection Status No. 59 97 234 275 362 543 54 135 173 Presence of__________________________________________________________________________ HeartwormVaccinated A1.sup.1 71 <71 71 192 71 192 192 71 71 -and Challenged A2.sup.2 A3.sup.2 A4 71 71 0 71 192 .sup. 192.sup.3 + A5 71 ND 516 192 192 192 192 192 ND - B1 0 71 0 71 71 71 ND ND ND - B2 71 71 192 192 192 71 71 71 71 - B3.sup.3 B4 ND 71 192 516 1341 516 1341 516 516 - B5 0 71 192 516 192 192 192 192 192 - B7 0 71 01192 71 71 71 71 71 -Not Vaccinated A6 0 0 71 192 516 1341.sup.3 +Not Challenged B6.sup.2 0 0 71Vaccinated C1 0 71 192 192 71 71 71 71 71 -Not Infected C2 0 0 71 192 ND 192 71 71 71 -Not Vaccinated D1F2 71 516 516 +Infected D2F2 71 192 192 +__________________________________________________________________________ .sup.1 Vaccinated dogs on Days 0, 1, 25, 27. Infected dogs on Day 594 .sup.2 A2 found dead on Day 62, no autopsy. A3 found dead on Day 103, no autopsy. B3 found dead on Day 93, no autopsy. B6 found dead on day 254, autopsy, no adult heartworms, no micorfilaria. .sup.3 Micofilaria detected in blood before dog was infected.

Efficacy Test No. 2

All dogs inoculated either SC or intramuscularly (IM) with 100 or 200 .mu.g of the vaccine antigen adjuvanted with either Quil A, Quil A 45% oil, and Montanide 888, or 5% oil and polyol L121 developed an antibody response to heartworm antigen (Table 2). Dogs inoculated SC with 40, 4 or 0.4 .mu.g heartworm antigen per dose and adjuvanted with quil A, 45% oil, and Montanide 888 also showed increased anti-heartworm antibody titers following vaccination, particularly the second vaccination (Tables 3 and 4).

TABLE 2__________________________________________________________________________Effect of Different Adjuvants and Route of Vaccinationon the Antibody Response of Dogs to Heartworm Antigen Antigen Geometric Mean Hemaglutination Titer Concen- Days Post First Days Post Second tration Dog Vaccination VaccinationAdjuvant (.mu.g/ml) Route No. 0 7 14 21 7 14 21 28 56__________________________________________________________________________Quil A.sup.1 100 SC DB44 32 64 256 128 1024 256 256 32 112 DA26 24 64 128 128 2048 137 256 128 160 DB3 12 46 256 128 168 137 256 128 109GM Titer 21 73 203 128 1172 169 256 81 127Quil A.sup.1 100 IM OIA3 64 64 512 256 3072 >2560 168 512 672 HUA3 64 48 384 192 1536 512 384 128 192 PFA3 64 32 256 256 2098 512 96 512 160GM Titer 64 46 369 233 2130 >876 305 323 274Quil A.sup.1 100 SC LEA3 48 384 1024 1024 1536 768 >1536 256 373M888.sup.2, Oil.sup.3 OVA3 64 64 354 256 8192 512 512 768 405 IVA3 32 96 10224 384 1024 768 192 192 181GM Titer 46 133 738 465 2344 671 >533 335 301Quil A.sup.1 100 IM WDF3 32 48 384 1536 768 768 256 256 384M888.sup.2, Oil.sup.3 WJF3 16 64 512 192 2048 512 256 256 224 XKF3 128 >384 512 1024 4096 640 >1536 768 >795GM Titer 40 >106 465 671 1861 631 >465 369 >409Quil A.sup.1 100 SC XXF3 32 64 1536 1024 >12288 768 512 768 >850Polyol.sup.L121, 4 QYD3 16 96 512 128 2048 1024 384 128 107Oil.sup.5 WYF3 128 32 512 128 1536 192 384 384 256GM Titer 40 58 738 256 >3381 533 423 335 284Quil A.sup.1 100 IM DB2 128 16 128 96 512 256 192 128 56Polyol.sup.L121 DB27 32 12 192 128 1536 256 64 96 91Oil.sup.5 DB22 64 32 384 384 2048 768 512 96 235GM Titer 64 18 211 168 1172 369 185 106 106Alginate 200 SC 26 32 48 24 48 192 96 128 128 144 1 16 16 48 64 48 64 1024 32 32 DA48 48 ND 32 64 96 48 96 64 96GM Titer 29 28 33 58 96 27 233 64 76__________________________________________________________________________ .sup.1 300 .mu.g Quil A per dose .sup.2 5% Montanide 888 .sup.3 45% Drakeol 6VR oil .sup.4 5% Polyol L121 .sup.5 5% Drakeol 6VR oil TABLE 3__________________________________________________________________________Effect of Adjuvant and Antigen Concentration on theHA Titer of Dogs to D. immitis Antigen Geometric Mean Hemaglutination Titer Days Post First Days Post Second Antigen Dog Vaccination VaccinationAdjuvant Concentration .mu.g/ml No. 0 7 14 21 7 14 21 28 56__________________________________________________________________________Alginate 40 94 12 64 32 64 32 64 96 24 48 83 8 32 16 32 96 32 64 32 96 80 12 64 48 64 48 64 128 64 48 Geometric Mean 10 51 29 51 53 52 92 37 60 55 32 32 64 128 128 192 256 192 64 40 100 ND 96 96 128 256 256 1024 512 84 81 16 64 24 64 256 384 96 256 192 Geometric Mean 23 58 53 101 203 266 293 293 168Quil A/ 53 16 32 32 192 768 512 1024 768 1536Drakeol Oil/ 4 73 ND 96 64 128 128 96 128 32 192Montanide 888 90 128 64 64 128 32 >768 768 768 384 Geometric Mean 45 58 51 128 147 >335 465 266 484 121 ND 128 24 32 64 64 128 32 48 0.4 DA49 128 48 64 96 128 32 256 48 192 DA47 48 64 24 64 48 32 128 48 64 Geometric Mean 78 73 33 58 23 40 161 42 84__________________________________________________________________________ TABLE 4__________________________________________________________________________Response of Dogs to 40 .mu.g of Heartworm Vaccine Adjuvanted withQuil A (300 .mu.g) and 5% Drakeol Oil Days Post First Days Post SecondRoute of Dog Vaccination VaccinationVaccination No. 0 7 14 21 7 14 21 28 56__________________________________________________________________________Sc 88 24 48 512 384 768 1024 512 512 192 124 16 64 384 768 2048 768 512 512 192Geometric Mean Titer 20 55 443 543 1254 887 627 512 192IM 108 16 128 192 96 128 256 192 256 128 102 48 256 >1536 >1536 1024 1536 512 512 192Geometric Mean Titer 23 181 >543 >384 326 627 314 362 257__________________________________________________________________________

Efficacy Test No. 2 (Cont.)

Increases in PHA anti-heartworm antigen antibody titers following challenge infection and results of challenge are shown in Tables 5 and 6. Most vaccinated dogs responded to challenge with an increase in PHA titer. Dogs inoculated with vaccine containing Quil A, 45% oil and Montanide 888 developed the highest antibody titers post challenge as they did post vaccination. Dogs inoculated with vaccine adjuvanted with alginate showed the smallest increase in antibody titer following challenge.

The 3 dogs that were inoculated with vaccine antigen adjuvanted with alginate, however, were all free of adult heartworm at the time of necropsy. One of three dogs inoculated IM and 1 of 3 dogs inoculated SC with vaccine antigen adjuvanted with Quil A, 5% oil and polyol 121 were also protected from infection. Only 1 other vaccinated dog was free of heartworm following challenge. This dog was inoculated SC with 4 .mu.g of vaccine antigen adjuvanted with Quil A, 45% oil, and 5% Montanide 888.

None of the non-vaccinated challenge control dogs were free of adult heartworms.

TABLE 5__________________________________________________________________________Effect of Different Adjuvants and Route of Vaccinationon the Response of Vaccinated Dogs to Challenge Reciprocal of HA Titer Weeks Post Challenge Results of ChallengeAdjuvant Route Dog No. 0 3 6 10 12 15 18 21 (Number of__________________________________________________________________________ Heartworms)Quil A.sup.1 SC DB44 128 64 24 64 48 96 64 64 13 DA26 768 96 256 128 128 64 64 ND 3 DB3 192 128 64 128 96 48 32 96 1GM Titer 266 92 73 102 84 67 51 78Quil A.sup.1 IM OIA3 384 512 384 128 128 192 768 4096 13 HUA3 384 256 128 128 192 256 384 512 6 PFA3 32 768 512 256 96 192 >2048 ND 7GM Titer 168 465 293 161 133 211 >845 1448Quil A.sup.1 SC LEA3 64 192 512 512 192 192 192 512 4M888 Oil CVA3 256 1024 768 512 768 192 >2048 1024 17 IVA3 192 96 256 384 384 128 1024 384 11GM Titer 147 266 465 465 384 168 >738 586Quil A.sup.1 IM WDF3 96 768 512 512 512 256 384 4096 11M888 Oil WJF3 40 192 192 256 64 96 128 384 ND(+).sup.4 XKF3 48 192 512 512 64 128 128 768 ND(+).sup.4GM Titer 57 305 369 406 128 147 185 1065Quil A.sup.1 SC XXF3 64 512 1024 768 192 192 512 512 4Polyol Oil QYD3 48 256 384 192 192 96 192 128 0 WYF3 48 128 192 96 96 128 384 512 10GM Titer 53 256 423 242 152 133 335 323Quil A.sup.1 IM DB2 24 96 48 64 192 96 192 512 0Polyol Oil DB27 96 192 128 64 64 24 256 192 6 DB22 32 512 512 128 256 128 256 ND 2GM Titer 42 211 147 81 147 67 233 314Alginate.sup.2 SC 26 69.sup.3 48 96 32 128 32 96 192 0 1 16 24 48 48 32 32 192 384 0 DA48 32 32 256 96 128 384 512 ND 0GM Titer 32 33 106 53 81 73 211 272Non-Vaccinates DA88.sup.3 192 512 384 96 48 64 128 192 22 10 32 32 64 48 48 24 32 67.sup.4 6 CT24 48 96 96 96 128 96 128 384 4 CT25 32 64 128 32 64 32 128 192 4 132 32 32 32 24 48 48 128 64 14 138 32 24 32 32 48 32 384 512 ND(+).sup.4 147 64 32 96 64 128 128 >2048 384 ND(+).sup.4 144 16 50 32 128 1024 192 1024 .sup. 516.sup.4 8GM Titer 42 50 75 55 93 60 >226 222__________________________________________________________________________ .sup.1 Challenged 17 weeks post 2nd vaccination. Dogs were vaccinated wit 100 .mu.g/ml dose of heartworm antigen. .sup.2 Challenged 11 weeks post 2nd vaccination. Dogs were vaccinated wit 200 .mu.g/ml dose of heartworm antigen. .sup.3 This dog was probably exposed to D. immitis prior to challenge. .sup.4 Dogs not necropsied but have Microfilaria in their blood. TABLE 6__________________________________________________________________________Effect of Concentration of Heartworm Antigen on theResponse of Dogs to D. immitisProteinConcentrationof Antigen.sup.2 Weeks Post Dog Reciprocal of HA Titer Weeks Post Challenge.sup.1 Route of Challenge(.mu.g/1 ml dose) 2nd Vacc. No. 0 3 6 10 12 15 18 21 (No. of__________________________________________________________________________ Heartworms)100 17 LEA3 64 192 512 512 192 192 192 512 4 OVA3 256 1024 768 512 768 192 >2048 1024 17 IVA3 192 96 256 384 384 128 1024 384 11GM Titer 147 266 465 465 384 168 >738 58640 11 55 64 128 96 256 64 192 192 3072 13 100 192 256 512 192 256 512 1024 768 7 81 256 >3072 1024 512 128 48 192 768 24GM Titer 147 >465 369 293 128 168 335 12190.4 11 121 16 16 64 32 192 384 384 256 8 DA49 16 128 128 64 96 128 256 192 10 DA47 24 32 128 128 64 32 96 192 14GM Titer 18 32 102 128 106 116 211 211 DA88.sup.3 192 512 384 96 48 64 128 192 22 10 32 32 64 48 48 24 32 64 6 CT24 48 96 96 96 128 96 128 384 4 CT25 32 64 128 32 64 32 128 192 4 132 32 32 32 24 48 48 128 64 14 138 32 24 32 32 48 32 384 512 ND(+).sup.4 137 64 32 96 64 128 128 >2048 384 ND(+).sup.4 144 16 16 32 128 1024 192 1024 512 8GM Titer 42 50 75 55 93 60 >226 222__________________________________________________________________________ .sup.1 Alginate group in Table 3 not challenged. .sup.2 Heartworm antigen is adjuvanted with Quil A (300 .mu.g/ml) in a waterin-oil emulsion containing Montanide 888. The vaccines were administered SC. .sup.3 This dog was probably exposed to D. immitis before challenge. .sup.4 Dogs not necropsied but have microfilaria in their blood.

The preceding examples demonstrate discovery of a vaccine that will aid in the prevention of parasitic disease caused by Dirofilaria and, in particular, of heartworm in dogs. The efficacy of the vaccine was measured by the protection of dogs against a challenge of infective third stage larvae (L3) of D. immitis.

The vaccine antigen, adjuvanted in different ways, stimulated the production of serum antibodies that were detected by the PHA antibody test. However, some vaccines did not stimulate as great an antibody response as others. Vaccine antigen adjuvanted with alginate stimulated very low levels of anti-heartworm antibody compared to vaccine antigen adjuvanted with other adjuvants, particularly, Quil A combined with 45% oil and 5% Montanide 888 (Table 2).

Although high levels of anti-heartworm antibody was found in the serum of dogs inoculated with vaccine antigen adjuvanted with Quil A, oil and Montanide 888, these antibodies were not associated with enhanced protection against challenge. Dogs that were best protected against challenge were dogs that had comparatively low levels of antibody following both vaccination and challenge. The vaccine antigen was most effective as an aid in the prevention of heartworm when it was adjuvanted with one of the two carbohydrate polymers, especially alginate. Six of 7 dogs (86%) in Efficacy Test No. 1, and 3 of 3 dogs (100%) in Efficacy Test No. 2 that were inoculated with vaccine antigen adjuvanted with alginate were protected against challenge. Two of 6 dogs that were inoculated with heartworm antigen and an adjuvant containing polyol L121 were also protected against challenge. One hundred percent (10/10) of infected but non-vaccinated dogs were found to have adult heartworm.

Results of Efficacy Test No. 2 suggested that low concentrations of antigen (100 .mu.g/dose) protect against challenge. One heartworm free vaccinate was inoculated with only 4 .mu.g antigen. This antigen was adjuvanted with Quil A, oil, and Montanide 888.

The above description and examples illustrate particular constructions including the preferred embodiments of the solution. However, the invention is not limited to the precise constructions described herein but, rather, encompasses all modifications and improvements thereof encompassed within the scope of the claims which follow.

Claims

1. A vaccine for protecting a mammal against infection by Dirofilaria which comprises an effective, non-toxic amount of water-soluble fraction of an extract of adult Dirofilaria organisms and of an acid-soluble fraction of an extract of adult Dirofilaria organisms.

2. The vaccine of claim 1 for protecting a canine animal against infection by D. immitis wherein the extract is of adult D. immitis organisms.

3. The vaccine of claim 2 wherein the water-soluble fraction is soluble at pH 6.5 to 7.5 and the acid-soluble fraction is soluble at pH 3 to 5 and the ratio by weight of the water-soluble fraction to acid-soluble fraction is 10:1 to 1:5.

4. The vaccine of claim 3 in which the ratio by weight of water-soluble fraction to acid-soluble fraction is about 4:1.

5. The vaccine of claim 3 or 4 which is adjuvanted.

6. The vaccine of claim 5 wherein the adjuvant is a carbohydrate polymer.

7. The vaccine of claim 6 in which the adjuvant is 1% to 5% alginate.

8. The vaccine of claim 4 in a 0.5 to 3 ml dosage unit in which the combined amount of water-soluble and acid-soluble fractions is 0.5 to 200 .mu.g, in saline buffered to pH 6.5 to 7.5, the vaccine is adjuvanted with 2.5% alginate and the vaccine contains about 0.01% merthiolate.

9. A process for preparing a vaccine for protecting a mammal against infection by Dirofilaria which comprises (i) disrupting Dirofilaria adult heartworms to prepare an extract thereof; (ii) separately collecting a water soluble fraction thereof and an acid-soluble fraction thereof and (iii) combining the two fractions in a pharmaceutically acceptable carrier.

10. The process of claim 9 in which the Dirofilaria adult heartworms are Dirofilaria immitis.

11. The process of claim 9 in which the water-soluble fraction is soluble at pH 6.5 to 7.5 and the acid-soluble fraction is soluble at pH 3 to 5 and the ratio by weight of the water-soluble fraction to acid-soluble fraction is 10:1 to 1:5.

12. The process of claim 10 in which, in step (iii), the two fractions are combined in a ratio of about 4:1 (w/w) water-soluble:acid soluble.

13. The process of claim 10 or 11 which further comprises combining the water-soluble and acid-soluble fractions with an adjuvant.

14. The process of claim 13 in which the adjuvant is a carbohydrate polymer.

15. The process of claim 13 in which the adjuvant is 1% to 5% alginate.

16. The process of claim 12 in which the oombined amount of water-soluble and acid-soluble fractions is 0.5 to 200 .mu.g per dose volume, the dose volume being 0.5 to 3 ml; the vaccine is buffered to pH 6.5 in saline, the vaccine is adjuvanted with 2.5% alginate; and, about 0.01% merthiolate is added to the vaccine.

17. A method for eliciting an immune response in a mammal to Dirofilaria which comprises internally administering to the mammal an effective, non-toxic amount of a water-soluble fraction of an extract of adult Dirofilaria organisms and of an acid-soluble fraction of an extract of adult Dirofilaria organisms.

18. The method of claim 17 for protecting a canine animal against infection by D. immitis wherein the extract is of adult D. immitis organisms.

19. The method of claim 17 wherein the water soluble fraction is soluble at pH 6.5 to 7.5 and the acid-soluble fraction is soluble at pH 3-5 and the ratio by weight of the water-soluble fraction to acid-soluble fraction is 10:1 to 1:5.

20. The method of claim 18 in which the ratio by weight of water-soluble fraction to acid-soluble fraction is about 4:1.

21. The method of claim 18 or 19 in which the water-soluble and acid-soluble fractions are administered with an adjuvant.

22. The method of claim 21 in which the adjuvant is a carbohydrate polymer.

23. The method of claim 21 in which the adjuvant is 1% to 5% alginate.

24. The method of claim 20 in which the combined amount of water-soluble and acid-soluble fractions is 0.5 to 200 .mu.g per dose volume, the dose volume being 0.5 to 3 ml; the vaccine is buffered to pH 6.5 in saline, the vaccine is adjuvanted with 2.5% alginate; and, about 0.01% merthiolate is added to the vaccine.