Treatments for Invert Pathogens
By Dana Riddle
Study of invertebrate pathogens is still in its infancy with most research having been conducted on intensely cultured animals such as shellfish.
With recent advances in captive culture of Tridacna calms, soft corals and stony corals, the need exists for medicines to combat invertebrate pathogens.
This short paper will review our current knowledge.
Invertebrates are susceptible to a variety of ailments. Infective agents include viruses, rickettsiae, chlamydiae, mycoplasmas, bacteria, fungi, algal cells and protozoa (Peters, 1988). Diseases affect the life span, life cycle, abundance, reproduction, metabolic performance and tolerance to natural and man-made stress (Kinne, 1980).
Currently, treatment of coral and Tridacna diseases is limited to freshwater dips (which is effective against platyhelminthes (flatworms) and some bacterial or protozoal infections.) Soft corals such as Sinularia (Dead Man's Hand), Sarcophyton (Leather corals) and some of the sturdier stony corals (e.g. Catalaphyllia - Elegance corals) can withstand this treatment with little or no lasting harm. Small-polyped stony (SPS) corals such as Acropora (Staghorn corals), Porites and others may be killed or made ill by this treatment (Antonius, 1988).
Bacteria
Bacteria are single celled organisms about 1 µm in diameter. Most possess a rigid cell wall. All lack a true nucleus and are thus considered prokaryotic. Bacteria may be classified in many ways; a negative or positive reaction to a Gram stain is but one. Gram-negative bacteria lose a stain or are decolorized by alcohol and generally possess a cell wall more complex than gram-positive bacteria (which, conversely, retain Gram's stain or resist decoloring by alcohol and have cell walls composed of peptidoglycan and teichoic acid).
Marine sediments are predominated by two bacteria - Vibrio and Pseudomonas (DiSalvo, 1973); the remainder (about 30%) are numerous other genuses, including Moraxella, Nitrobacter, Nitrosomonas, etc.
-Vibrio - Genus of gram-negative bacteria (Family Spirillaceae). Vibrio parahaemolyticus and V. vulnificus inhabit many marine organisms. V. alginolyticus and V. anguillarum can cause mass mortalities in clams (Delbeek and Sprung, 1994). Unidentified Vibrio species are thought to be a natural control for Acanthaster - the Crown-of-Thorns starfish (Sutton et al, 1988). V. tubiashii is a known pathogen of invertebrates.
Pseudomonas - A genus of gram-negative, strictly anaerobic bacteria. Some species are pathogenic to vertebrates, plants and invertebrates. Sutton et al (1988) describes Pseudomonas as a pathogen of the Crown-of-Thorns starfish.
-Moraxella - A genus of bacteria found as parasites and pathogens in warm blooded animals. It has been noted as a starfish pathogen as well.
-Mycoplasma - A genus of pleomorphic (various shapes found in a single species), gram-negative, aerobic to facultative anaerobic microorganisms.
-Chlamydiales - An order of coccoid (spherical), gram-negative bacteria that multiply within the cytoplasm (cellular fluids exclusive of the nucleus).
-Rickettsiae - An order of gram-negative bacteria occurring as short rods, chained cocci, and pleomorphic forms. They are non-motile. Pathogenic rickettsiae include the organisms which cause Typhus and Rocky Mountain Spotted Fever.
CORAL DISEASES
Arnfried Antonius has authored numerous papers on coral pathogens. He notes that many bacteria normally live on or within corals. Various environmental factors such as temperature, salinity, pollution (or more correctly eutrophication), exposure to toxic metabolites and others can induce stress and subsequently make the coral susceptible to diseases from these naturally-occurring micro-organisms. He lists the coral diseases as:
BLACK BAND DISEASE (BBD)
The blue-green cyanobacteria Phormidicum corallyticum (Antonius, 1981) and Oscillatoria (Littler et al, 1989) are the apparent causes. These bacteria cause coral tissue necrosis by exuding a toxic metabolite. The dead coral skeleton left behind is in stark contrast to the "black band" of cyanobacteria. BBD correlates with excessive water column nutrient levels and temperature. BBD has been found to disappear at temperatures below 26 degrees C (78.8 degrees F). This disease is known to occur strictly in shallow-water.
Antonius (1988) found many corals not susceptible to BBD in nature to be readily infected in aquaria. A short listing of corals found in the Atlanta area pet shops and their susceptibility to BBD is listed below.
I = Immune R = Resistant S= Susceptible Slow (tissue loss 1mm per day) M = Susceptible Medium (tissue loss 1 to 3 mm per day) F= Susceptible Fast (tissue loss 3 to 5 mm per day)
Stylophora - S
Pocillopora - M
Acropora - F (12 species)
Montipora - not tested, but I have a M. digitata that has been infected by a red cyanobacteria and has lost tissue at a very slow rate.
Pavona - S
Cycloseris - I
Fungia - I (5 species)
Herpolitha - I
Porites - R (5 species)
Favia stelligera - M
Favia - R (2 species)
Favites chinensis - S
Favites - R (4 species)
Goniastrea retiformis - F
Goniastrea pectinata - M
Platygyra daedalea - R
Platygyra lamellina - M
Hydnophora microconos - M
Hydnophora exesa - S
Galaxea - R
Tubipora - coral tissue initially destroyed, then the coral rejected the disease; that is, it attacked and overcame the infection. Only occurrence in over 50 species tested.
WHITE BAND DISEASE (WBD):
Black band Disease is easy to identify; White Band Disease is not. With SPS corals, it is difficult to distinguish between "bleaching" and WBD. Researchers well acquainted with the disease had to scrape tissue from species of Acropora to determine if an infection existed. WBD advances and destroys tissue with no apparent cause. It occurs most often in upper reef areas. This disease seems to occur all year round with slightly more cases during warm weather. Antonius (1988) noted Acropora species to be infected in pristine waters. The stony coral Porites may also be infected. Antonius made a correlation of various environmental factors relating to an increase in WBD. They are: strong wave action, salinity swings due to rainfall or run-off, and, possibly, toxic metabolites from naturally occurring reef algae turfs.
Microscopic examinations of infected tissues are discussed by Peters et al (1983) and these tissues were found to contain "unusual" gram-negative, rod-shaped bacteria. Further, Dustan (1977) found healthy colonies could be infected by exposure to diseased tissues from other colonies, suggesting a viral, bacterial or fungal cause.
SHUT DOWN REACTION (SDR): This disease is likely to be stress related as the coral very quickly fails to expand and turns to a decaying mass. SDR is apparently not related to temperature stress as Delbeek and Sprung (1994) suggest; however, lower temperatures may slow SDR which suggests a bacterial or fungal cause.
(CONT)
By Dana Riddle
Study of invertebrate pathogens is still in its infancy with most research having been conducted on intensely cultured animals such as shellfish.
With recent advances in captive culture of Tridacna calms, soft corals and stony corals, the need exists for medicines to combat invertebrate pathogens.
This short paper will review our current knowledge.
Invertebrates are susceptible to a variety of ailments. Infective agents include viruses, rickettsiae, chlamydiae, mycoplasmas, bacteria, fungi, algal cells and protozoa (Peters, 1988). Diseases affect the life span, life cycle, abundance, reproduction, metabolic performance and tolerance to natural and man-made stress (Kinne, 1980).
Currently, treatment of coral and Tridacna diseases is limited to freshwater dips (which is effective against platyhelminthes (flatworms) and some bacterial or protozoal infections.) Soft corals such as Sinularia (Dead Man's Hand), Sarcophyton (Leather corals) and some of the sturdier stony corals (e.g. Catalaphyllia - Elegance corals) can withstand this treatment with little or no lasting harm. Small-polyped stony (SPS) corals such as Acropora (Staghorn corals), Porites and others may be killed or made ill by this treatment (Antonius, 1988).
Bacteria
Bacteria are single celled organisms about 1 µm in diameter. Most possess a rigid cell wall. All lack a true nucleus and are thus considered prokaryotic. Bacteria may be classified in many ways; a negative or positive reaction to a Gram stain is but one. Gram-negative bacteria lose a stain or are decolorized by alcohol and generally possess a cell wall more complex than gram-positive bacteria (which, conversely, retain Gram's stain or resist decoloring by alcohol and have cell walls composed of peptidoglycan and teichoic acid).
Marine sediments are predominated by two bacteria - Vibrio and Pseudomonas (DiSalvo, 1973); the remainder (about 30%) are numerous other genuses, including Moraxella, Nitrobacter, Nitrosomonas, etc.
-Vibrio - Genus of gram-negative bacteria (Family Spirillaceae). Vibrio parahaemolyticus and V. vulnificus inhabit many marine organisms. V. alginolyticus and V. anguillarum can cause mass mortalities in clams (Delbeek and Sprung, 1994). Unidentified Vibrio species are thought to be a natural control for Acanthaster - the Crown-of-Thorns starfish (Sutton et al, 1988). V. tubiashii is a known pathogen of invertebrates.
Pseudomonas - A genus of gram-negative, strictly anaerobic bacteria. Some species are pathogenic to vertebrates, plants and invertebrates. Sutton et al (1988) describes Pseudomonas as a pathogen of the Crown-of-Thorns starfish.
-Moraxella - A genus of bacteria found as parasites and pathogens in warm blooded animals. It has been noted as a starfish pathogen as well.
-Mycoplasma - A genus of pleomorphic (various shapes found in a single species), gram-negative, aerobic to facultative anaerobic microorganisms.
-Chlamydiales - An order of coccoid (spherical), gram-negative bacteria that multiply within the cytoplasm (cellular fluids exclusive of the nucleus).
-Rickettsiae - An order of gram-negative bacteria occurring as short rods, chained cocci, and pleomorphic forms. They are non-motile. Pathogenic rickettsiae include the organisms which cause Typhus and Rocky Mountain Spotted Fever.
CORAL DISEASES
Arnfried Antonius has authored numerous papers on coral pathogens. He notes that many bacteria normally live on or within corals. Various environmental factors such as temperature, salinity, pollution (or more correctly eutrophication), exposure to toxic metabolites and others can induce stress and subsequently make the coral susceptible to diseases from these naturally-occurring micro-organisms. He lists the coral diseases as:
BLACK BAND DISEASE (BBD)
The blue-green cyanobacteria Phormidicum corallyticum (Antonius, 1981) and Oscillatoria (Littler et al, 1989) are the apparent causes. These bacteria cause coral tissue necrosis by exuding a toxic metabolite. The dead coral skeleton left behind is in stark contrast to the "black band" of cyanobacteria. BBD correlates with excessive water column nutrient levels and temperature. BBD has been found to disappear at temperatures below 26 degrees C (78.8 degrees F). This disease is known to occur strictly in shallow-water.
Antonius (1988) found many corals not susceptible to BBD in nature to be readily infected in aquaria. A short listing of corals found in the Atlanta area pet shops and their susceptibility to BBD is listed below.
I = Immune R = Resistant S= Susceptible Slow (tissue loss 1mm per day) M = Susceptible Medium (tissue loss 1 to 3 mm per day) F= Susceptible Fast (tissue loss 3 to 5 mm per day)
Stylophora - S
Pocillopora - M
Acropora - F (12 species)
Montipora - not tested, but I have a M. digitata that has been infected by a red cyanobacteria and has lost tissue at a very slow rate.
Pavona - S
Cycloseris - I
Fungia - I (5 species)
Herpolitha - I
Porites - R (5 species)
Favia stelligera - M
Favia - R (2 species)
Favites chinensis - S
Favites - R (4 species)
Goniastrea retiformis - F
Goniastrea pectinata - M
Platygyra daedalea - R
Platygyra lamellina - M
Hydnophora microconos - M
Hydnophora exesa - S
Galaxea - R
Tubipora - coral tissue initially destroyed, then the coral rejected the disease; that is, it attacked and overcame the infection. Only occurrence in over 50 species tested.
WHITE BAND DISEASE (WBD):
Black band Disease is easy to identify; White Band Disease is not. With SPS corals, it is difficult to distinguish between "bleaching" and WBD. Researchers well acquainted with the disease had to scrape tissue from species of Acropora to determine if an infection existed. WBD advances and destroys tissue with no apparent cause. It occurs most often in upper reef areas. This disease seems to occur all year round with slightly more cases during warm weather. Antonius (1988) noted Acropora species to be infected in pristine waters. The stony coral Porites may also be infected. Antonius made a correlation of various environmental factors relating to an increase in WBD. They are: strong wave action, salinity swings due to rainfall or run-off, and, possibly, toxic metabolites from naturally occurring reef algae turfs.
Microscopic examinations of infected tissues are discussed by Peters et al (1983) and these tissues were found to contain "unusual" gram-negative, rod-shaped bacteria. Further, Dustan (1977) found healthy colonies could be infected by exposure to diseased tissues from other colonies, suggesting a viral, bacterial or fungal cause.
SHUT DOWN REACTION (SDR): This disease is likely to be stress related as the coral very quickly fails to expand and turns to a decaying mass. SDR is apparently not related to temperature stress as Delbeek and Sprung (1994) suggest; however, lower temperatures may slow SDR which suggests a bacterial or fungal cause.
(CONT)
