AU2002217423A1 - A process for preparation of a microbial agent - Google Patents

Description

A p roces s for p reparation o f a microb ial agenfc

FIELD OF INVENTION

The present invention relates to a process for preparation of a microbial agent containing a ciliated protozoa, Chilodonella uncinata, for mosquitoes vectors of human diseases.

PRIOR ART

Over the past half-century, the primary tactics employed to control target mosquito population have involved the use of chemical larvicides and adulticides. Such tactics, although effective when they were initially employed, tend to eventually result in the development of resistance in the target mosquito population, severe suppression of non-target organisms, and/or general pollution of the environment when these tactics are the only ones employed or otherwise overused.

Thus, more biorational approaches are needed to manage mosquito population of public health importance. One such approach would be to combine a chemical insecticide that is highly specific for mosquitoes and otherwise relatively harmless to the environment with one or more biological control agents effective against these insects.

Thus, it is known to use Bacillus thuringensis as a microbial agent. However, it has been found that such agents do not propagate in the environment. Thus, it becomes necessary to constantly re-apply the microbial agent, and consequentially raises the end cost of the treatment. Coelomomyces sp. is a fungal pathogen and its efficacy has been evaluated in rice fields for mosquito control. A disadvantage associated with such a microbial agent is that it possesses a complex life cycle and it requires an intermediate host for its continuous reproduction.

Two species of Nematodes, viz. Romanomermis culicivorax and R. iyengari are known as microbial agents. A disadvantage is that such nematodes require in- vivo production, and are highly sensitive to salinity, organic pollution, temperature extremes and certain agrochemical used in paddy cultivation.

Protozoan pathogens of mosquitoes are ubiquitous and at times produce periodic outbreaks of disease in mosquito larvae those results in severe decline in mosquito population. The microsporidia (Thelohanidae, Nosematidae) and ciliates of the genera Lambornella and Tetrahymena are some of the most common and best-studied protozoa. Of these, Lambornella was found to be highly pathogenic to natural population of tree hole breeding mosquito larvae. A disadvantage of all microsporidians of biological control interest is that it must be grown in living host or host cell culture increasing the cost of producing these agents. Further, the use of insect cell cultures to mass-produce microsporidia is not yet economically feasible because of limitations on the mass culture of insect cell themselves and because the yield of microsporodia spores per infected cell is too low.

OBJECTS OF THE INVENTION

An object of this invention is to propose a process for preparation of a microbial agent containing a ciliated protozoa, Chilodonella uncinata, for mosquitoes vectors of human diseases. Another object of this invention is to propose a process for preparation of a microbial agent containing a ciliated protozoa, Chilodonella uncinata, for mosquitoes vectors of human diseases and where the protozoa can easily reproduce.

Still another object of this invention is to propose a process for preparation of a microbial agent containing a ciliated protozoa, Chilodonella uncinata for mosquitoes vectors of human diseases which provides a mass killing of mosquito larvae.

Yet another object of this invention is to propose a process for preparation of a microbial agent containing a ciliated protozoa, Chilodonella uncinata for mosquitoes vectors of human diseases and wherein the ciliated protozoa is able to naturally recycle itself in various habitats.

A further object of this invention is to propose a process for preparation of a microbial agent containing a ciliated protozoa, Chilodonella uncinata for mosquitoes vectors of human diseases and wherein the ciliated protozoa for killing of mosquito larvae need not be repeatedly inoculated.

A still further object of this invention is to propose a process for preparation of a microbial agent containing a ciliated protozoa, Chilodonella uncinata for mosquitoes vectors of human diseases wherein the ciliated protozoa which when inoculated can be transmitted from the infected host adult mosquitoes to offspring.

Yet a further object of this invention is to propose a process for preparation of a microbial agent containing a ciliated protozoa, Chilodonella unpmata for mosquitoes vectors of human diseases and wherein the ciliated protozoa is robust against all aggressive environs. DESCRIPTION OF INVENTION:

According to this invention there is provided a microbial control agent for mosquito vectors of human diseases comprising a ciliated protozoa, and more particularly Chilodonella uncinata, and a carrier such as sand or distilled water and yeast.

Further according to this invention there is provided a method of killing mosquito larvae and particularly the species comprising Culex tritaeniorhynchus, Cx. pseudovishnui, Cx. (Cx) sp., Cx. (Lutzia) sp. and Anopheles hyrcanus group which comprises in allowing Chilodonella uncinata as a ciliated protozoa to be present in said host larvae, allowing the ciliated protozoa to form a hole in the wall of the larvae and to enter into the haemocoelomic cavity of the larvae and to thereby allow the ciliate to feed on the host larvae and simultaneously allowing the host larvae to grow and allow a multiplication of the ciliate, and whereby the multiplied ciliates kill the host larvae.

The composition containing Chilodonella uncinata reflected that Ch. uncinata in the formulation kills colonized mosquito larvae, viz. Aedes aegypti, Culex quinquefacitalus and Cx. tritaeniorhynchus. The Chilodonella uncinata was found to be highly pathogenic to susceptible host larva. Even a few of them were able to initiate chronic infection. Ch. uncinata has following attributes of a promising biological control agent against mosquito larvae particularly vectors of Japanese encephalitis: Would help mass killing of mosquito larvae

They can be transmitted from the infected- host adult mosquitoes to offsprings by virtue of their facility for trans-ovarian transmission

They are highly robust against all aggressive environmental condition like temperature, dryness and changes in light intensity etc.

A desirable feature of microbial pathogens is that they are capable of reproduction and have the potential to amplify themselves in the field and cycle through pest population. Thus, the organism must be able to establish an ecological niche against competition from other organisms and must not be unduly sensitive to extremes of temperature, relative humidity or direct sunlight. It should have a high rate of reproduction and be capable of high rate of transmission and infection.

In accordance with the present invention, it has been found that the ciliated protozoa of the present invention has the advantageous properties described herein above.

Reference is now made to Table 1, which reflected that Ch. uncinata was detected to be pathogenic to mosquito larvae in nature.

TABLE 1

Type of habitats indicating number of mosquito larvae examined for Chilodonella uncinata infection.

1. Culex tritaeniorhynchus 2. Cx. pseudovishnui 3. Cx. (Lutzia) sp.

4. Cx. (Culex) sp. 5. Anopheles stephensi var. mysoriensis 6. An. hyrcanus gp.

The findings of small ciliates in the tissues of mosquito larvae indicates infection by at least one of the following: Chilodonella, Tetrahymena and Lambornella. A brief generic description and a dichotomous key to the species of the genus Chilodonella are provided. CILIATES OF MOSQUITO LARVAE

Ciliates belonging to genus Chilodonella have Body flat, dorso-ventrally compressed as shown in Fig. 1 with distinct pre oral beak (a), cilia of trophont (free swimming, non parasitic stage) distinct, cover most of ventrum; oral region usually behind pre oral suture (b), cytopharynx usually with well developed rod apparatus (c). In contrast, body of ciliates beloging to other pathogenic genera, viz. Tetrahymena and Lambornella is round in transverse section (Figs.2,3,4), uniformly covered with cilia; no distinct pre oral beak; oral region with well developed buccal apparatus (Figs. 2a,3Aa).

KEY TO INDIAN SPECIES OF CHILODONELLA

1. Contractile vacuole numerous, scattered; large size (130-150μ); macronucleus oval; cytopharyns long & straight (Fig.5)

Chilodonella cucullulns Contractile vacuole 1-3 in number

2. Contractile vacuole single (Fig.6,a); cytopharyns short & straight (6b)

Ch. rhesus Contractile vacuole two to three in number.

3. Contractile vacuole two in number; pre-oral kinety complete (Fig.7,a); cytopharyns short & straight (b); small size (30-50μm); macronucleus large and round, situated posterio-terminal (c).

Ch. uncinata Contractile vacuole two to three in number, largest posterio-terminal (Fig.8,a); cytopharynx spirally curved behind (b).

Ch. spiralidentis Chilodonella uncinata are small sized ciliates. Body strongely asymetrical, more than twice as long as broad, length 30 μm (mean), width 20 μm. Anterior extremity produced into a beak like projection. Ventral surface flattened, bearing longitudinal ciliary lines only on the anterior half of the body, those on the right half curved and running on to the beak, those on the left half ruiming straight. Dorsal surface convex. Cytostome ventral, situated in the anterior third of the body. Post oral kinety complete. Cytopharynx short & truncate, directed towards the left, with a distinct rod-apparatus. Contractile vacuole two. Macronucleus large (length 8 μm, width 7 μm) & rounded, with a small micronucleus ((2.0-2.5 μm) close to it as in key.

EXAMPLE

A. Problems Encountered In Detection, Isolation, Colonization & Identification of Ch. uncinata

Repeated cent percent mortality was observed in mosquito larvae of Culex tritaeniorhynchus within 24 hours of collection from paddy fields. However, a lot of difficulty was encountered in recognizing the causative pathogenic microbe due to the following :

1. A few species of lower invertebrates belonging to the genera viz. (Ciliated Protozoa: Paramecium, Euplotes, Stylonychia); Thecate Amoeba [Phyllum Protozoa] and a species of Rotifer were recorded many-a-times from the same natural habitats of mosquito larvae.

According to the literature and experts in the field (personal communication) none of these aforesaid micro-organisms has been recorded to be pathogenic to mosquito larvae. A species of Vorticella (ciliated Protozoa) was found attached to dead mosquito larvae. Vorticellids are not pathogenic to mosquito larvae. However, under special circumstances, when large number of individuals of Vortecellid get attached to one mosquito larva, with the result due to increased weight the larva is drowned and dead.

Dead mosquito larvae collected from paddy fields were washed in distilled water and kept in aliquots for a few days under laboratory condition and observed under microscope. Another dorso-ventrally flattened ciliated protozoa not noticed earlier now appeared in the water containing the dead larvae. In addition, dead larvae were then transparent and some infection as in (Fig.10) was noted under 100 X magnification. At that particular point there was an indication that probably this dorso-ventrally flattened ciliated protozoa (ciliate*) might be the causative microbe killing the mosquito larvae. Contents of those aliquots with contamination of other unwanted and aforesaid ciliates, etc. were discarded. Those containing the candidate (ciliate*) were filtered through 10 μm mesh. These were kept as such for some more days in enamel tray used for colonizing mosquito larvae. To an utter surprise when viewed under the microscope the number of (ciliate*) increased outside the dead mosquito larva and some of them were also found inside the body indicating that these pathogenic microbes were capable of escaping the carcasses of host larva after increasing their number at expense of internal tissues of the host.

To colonize under laboratory condition, available artificial media, viz. Cooked rice, boiled wheat grain, yeast tablet, wheat floor, etc. using glass/plastic beakers and the procedure was standardized. It was found that these (ciliates*) could be produced on mass scale under laboratory condition (Temp. 27±2°C), Humidity (70-80%) within 48-72 hours using yeast tablet with distilled water as a medium in glass container. Then the medium with the ciliates* is filtered through 10 μm mesh cloth and designated as Ch. uncinata (NICD BP-10). The concentration of (ciliate*) was counted using 10 μm of the formulation Ch. uncinata (NICD BP-10) on a clean glass slide using a compound microscope in 100 X magnification. The concentration is expressed as numbers/ml.

under study In the present invention, sterile sand was submerged in the isolate (BP- 10) and the sand was allowed to ' dry at room temperature in the laboratory to get the dry formulation designated as Chilodonella uncinata (NICD BP-11). In the dry formulation the pathogen, Ch. uncinata remain inactivated.

Batches of infected wild caught mosquito larvae as well as known concentration of the above formulation were kept with colonised mosquito larvae (Aedes aegypti, Culex quinquifaciatus and Anopheles stephensϊ) and it was found that infection could be induced in first two species under laboratory condition.

Isolation of ciliate Ch. uncinata from adult mosquitoes collected from the study areas in Haryana include keeping 25 female mosquitoes (Cx. tritaeniorhynchus) individually in glass specimen tubes with distilled water a procedure followed to raise single female colony. After a gap of 2-5 days, free-swimming form (also known as trophont as in Fig.14) appeared in the water of 23 specimen tubes. Eggs were laid in 5 specimen tubes. However, in some tubes, eggs failed to hatch while in others larvae died in 2^nd/3^rd instar stage. This indicates the promising capability of this ciliate to get dispersed to newer areas as well as transovarian transmission of Ch. uncinata from infected parent to offspring as shown in Fig.15. Effect of desiccation on the stability of the formulation Chilodonella uncinata (NICD BP-10):

The effect of dryness was evaluated following two simple ways:

i) A number of plastic cups containing Chilodonella uncinata (NICD BP-

10) were allowed to dry at room temperature, re-flooded with distilled water after a varying period of time and examined for revival of the pathogen using 1 OX magnification.

ii) One ml of the isolate Chilodonella uncinata (NICD BP-10) was added to 10 gms of sterile sand and was allowed to dry at room tempertaure.^" These were submerged in distilled water after a gap of 5, 10, 15, 20, 25 days and examined daily using 10X magnification for the revival of the pathogen.

Results: i) When re-flooded with distilled water Ch. uncinata reappear in the dry plastic. cups in a span of 2-5 days time.

ii) Dry and impregnated sterile sand with 1 ml of Chilodonella uncinata (NICD BP-10) when submerged in distilled water, Ch. uncinata reappear irrespective of prior period of dryness under room temperature.

This shows the ciliate is able to stand desiccation by encysted form and when re-flood excysted into free swimming stage.

This property of the microbial pathogen (Ch. uncinata) in the above formulation indicates it is desiccation resistant (robustness) and easy storage of the formulation. B. Chilodonella uncinata: Mode of entry inside the host body & subsequent histopathology

The free swimming dorso-ventrally flattened trophont form of Ch. uncinata in presence of susceptible mosquito larvae transform into parasitic form (theronts, as in Fig. 14). These parasitic theronts are extremely mobile, very small in size, nearly pointed to club shaped and they seeks 1^st and 2^nd instar mosquito larva. Then it get itself attached to a convenient site on the body of the larva, form small hole in the cuticle "cuticular invasive cyst" (Fig. 9) and reach the haemocoel of the host larva. On reaching the desired site i.e. (haemocoel) Ch. uncinata multiplies and form numerous endoparasitic ciliates/morphs (Figs. 10,11,12 & 13). These ciliates do not usually kill their host at an early stage but let them grow in size so that they also increase their number manifold. Finally when the larva dies these ciliates continue to increase their number for some more time and then transform into numerous trophonts. Moribund and deceased hosts release numerous trophonts, some of which differentiate into theronts that attack surviving predators (mosquito larvae). Those Ch. uncinata that cannot effectively penetrate through the host cuticular invasive cyst and make the free of the cuticle are trapped inside the later and are seen as melanized spots on the host larva (as observed in many times on Aedes aegypti.

After the above stages were demonstrated it became clear to understand the events that take place in the life history of otherwise free-swimming ciliate Ch. uncinata in presence of a susceptible host in the breeding habitat. This type of mode of entry of microbe from outside is known only in two cases namely. Lambornella (another ciliated protozoan) and Coelomomyces (parasitic fungi) of mosquito larvae. The former breeds in tree holes and parasitises Aedes sirensis and the latter require another intermediate host invertebrate in the form of copepodes (Crustaceans) for its production.

Reproduction in Ch. uncinata involves nuclear division and the separation of newly formed units. Separation occurs through simple binary fission (which is often noticed in the present study when yeast is added in the rearing medium) and into many daughter cells as endoparasitic ciliates ( inside the body of host mosquito larvae).

Claims

WE CLAIM:

1. A method of killing mosquito larvae and particularly the species comprising Culex tritaeniorhynchus, Cx. pseudovishnui, Cx. (Cx) sp., Cx. (Lutzia) sp. and Anopheles hyrcanus group which comprises in allowing Chilodonella uncinata as a ciliated protozoa to be present in said host larvae, allowing the ciliated protozoa to form a hole in the wall of the larvae and to enter into the haemocoelomic cavity of the larvae and to thereby allow the ciliate to feed on the host larvae and simultaneously allowing the host larvae to grow and allow a multiplication of the ciliate, and whereby the multiplied ciliates kill the host larvae.

2. A method as claimed in claim 1 wherein the ciliate withdraws from the host larvae when said larvae is killed.

3. A method as claimed in claim 1 wherein the ciliated protozoa is strongly flattened dorso-ventrally.

4. A method as claimed in claim 1 wherein the body ciliation of the protozoa is confined to ventral surface only.

5. A method as claimed in claim 1 wherein the ciliated protozoa has a distinct pre oral beak.

6. A method as claimed in claim 1 wherein the cytopharynx of the ciliated protozoa possess rod apparatus.

7. A microbial control agent for mosquito vectors of human diseases comprising a ciliated protozoa, and more particularly Chilodonella uncinata, and a carrier such as sand or distilled water and yeast