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This article was published in 1961
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.

The External Application of the Organic Phosphorus Compounds in Veterinary Medicine

B. HEFFER, B.V.Sc., Research Officer, William Cooper & Nephews (Australia) Pty. Limited

The search for different and more efficient insecticides for the control of insect pests of both animals and plants has been, and still is, spurred on by resistance, or the threat of resistance, developing in pest populations. Reports of insects developing degrees of resistance to even the newer insecticides are received much too frequently to allow for any complacency with regard to our present position.

We are fortunate in Australia that we have relatively few external parasites of economic importance as far as livestock are concerned, but we have a resistance problem in those that we do have. For instance the resistance developed by the sheep blowfly and the cattle tick to the chlorinated hydrocarbon insecticides. Overseas, resistance in pests in the household and public health fields, such as malarial mosquitos, is a greater problem than it is here, but our turn may come.

The organic phosphorus compounds brought with them a new approach to parasite and insect control by virtue of their systemic action. Stages in the life cycle of some external parasites which are found within or in very close contact with their host, can now be controlled by the oral, hypodermic or dermal administration of the insecticide. A good example is Warble Fly larvae in cattle.

The mode of action and metabolism of the organic phosphorus compounds is now reasonably well known. They interfere with the normal transmission of nerve impulses in the body by inhibiting the enzyme cholinesterase; leading to the accumulation of acetylcholine, which has been shown now to play a definite role in the metabolism of nervous tissue in insects, if not in synaptic transmission. Other enzymes also may be involved. The phosphorylation of the enzyme by the organic phosphorus compounds can be reversed, if it has not gone too far, by the administration of 2 P.A.M.; which, as will be seen later, is used in cases of organic phosphorus poisoning (Chamberlain et al. (1960). O'Brien et al. (1959) Kaplanis et al. (1959), Winteringham and Lewis (1959)).

The organic phosphorus compounds in common use in the veterinary field have been selected because of their relatively low mammalian toxicity, which in most cases, is out of proportion to their high toxicity to insects. The reason for this is that animals can degrade and eliminate the toxic residues or metabolites of these insecticides far more rapidly than insects. For example, malaoxin, the toxic metabolite of malathion, is almost eliminated from the mouse in approximately 3 hours; whereas in the cockroach this process may take up to 24 hours. (March et al. (1956), O'Brien (1957), Kruker et al. (1959).

ORGANIC PHOSPHORUS POISONING

The symptoms in the usual order of appearance are: Salivation, cough, dyspnoea, colic, stiffness or muscle tremor and collapse. (Radeleft and Woodard (1957). The specific antidote for organic phosphorus poisoning is ATROPINE. Dose rate for cattle: ¼ - 1 gr. subcutaneously, with or without the addition of 2 P.A.M. at the rate of 50 mg/kg. in 100 - 125 mls. of saline subcutaneously. Dose rate of Atropine for Sheep: 2 mg./kg. or approximately 1 grain per adult sheep: 1/3 given intravenously, 2/3 subcutaneously. This can be followed if necessary by 2 - 4 mg./kg. in 20 ml. peanut oil, given subcutaneously (Woodard (1957)).

The symptoms of organic phosphorus poisoning in humans are salivation, contraction of the pupils, nausea, respiratory distress, twitching, convulsions and finally paralysis of the respiratory centre. For the treatment of organic phosphorus poisoning in Man, Atropine is given at the rate of 1/60 - 1/30 grain every 1-hour with one gram 2 P.A.M. given intravenously. For human treatment refer to booklet "Agricultural Pesticides - A Synopsis of Toxicology and Treatment", by Dr. D. C. Trainor, published by the N.S.W. Department of Public Health (1959).

CATTLE PARASITES:

Cattle Ticks:

Organic phosphorus compounds are now widely used for the control of chlorinated hydrocarbon resistant cattle ticks. Those in common use in Australia are Delnav 0.075%, Asuntol 0.04% and Diazinon 0.04%. Treatment should commence in the spring before infestation becomes heavy. (Norris (1957)). Two dippings given at a 10 day interval will quickly kill off most of the ticks and then dipping should be repeated every twenty-one days until the infestation is light. These insecticides may be used in a dipping tank or through a cattle spray race. Both these methods are efficient if carried out properly.

Warble Fly (Hypoderma spp.)

Overseas, the organic phosphorus compounds have provided a highly effective means of controlling warbles, a parasite which, fortunately, we do not have in Australia. Some of the insecticides which have been used for this purpose are as follows:

(a) Ronnel:

Orally (100 mg./kg.)

In the feed (15-25 mg./kg.) for six to seven days

As a spray (2.5%)

(b) Asuntol:

As a spray (0.5%)

Scrubbed on the back (2%), 1 litre.

(c) Narlene:

Orally or intramuscularly (15-25 mg./kg.)

As a spray (1%)

(d) Dimethoate:

Orally (5-20 mg./kg. average 15 mg./kg.)

As a spray (0.25% - 1%).

Dimethoate is considered to have an inadequate safety margin and may be toxic at the higher levels (Wood, J. C. et al. (1959), Drummond and Graham (1959) Drummond and Moore (1960), Sharma et al. (1960)).

Nuche (Dermatobia hominis):

This is another parasite of cattle found in Central and South America, and has been treated with Neguvon (50 mg./kg. orally), Trolene (100 mg./kg. orally) and Narlene.

Cattle Lice:

Cattle Lice may be controlled by spraying with Diazinon (0.04%), Asuntol (0.04%), Malathion or Ruelene (0.5%). During the course of other experiments both Neguvon and Ruelene, when given orally, have been noticed to affect cattle lice populations.

SHEEP PARASITES:

Itch Mite:

Unfortunately the organic phosphorus compounds have not proved highly effective against Itch Mite in Australia. In South Africa, however, Malathion at 0.2% has been approved for use against this parasite (Murray (1957), Sinclair (1958)).

Lice and Keds:

As neither sheep lice nor keds have shown any resistance to the chlorinated hydrocarbon insecticides, the organic phosphorus compounds are not used to any great extent in this field. Diazinon is available for this purpose in Australia. Others that have been tried in America are Ronnel, Asuntol, Narlene and Delnav. all at 0.1%. Diazinon (0.01 - 0.02%) may be used in a plunge or shower dip. (Roth and Bigley (1959)).

Blowflies:

The relatively sudden failure of the chlorinated hydrocarbon insecticides to control the sheep blowfly stimulated wide research into the application of the organic phosphorus compounds for this purpose. Those in common use today are Diazinon (0.04%). Delnav (0.1%), and to a lesser extent Malathion (0.2%) as jetting fluids, and Diazinon (0.25%) as a tip spray. When these insecticides were first introduced, some complaints were received of inefficiency. However, when investigated, most were found due to inefficient application the result of "slap-dash" jetting techniques. For maximum efficiency both Delnav and Diazinon must be applied evenly and thoroughly to the area being treated. The combination of Diazinon and D.D.T. in powder form has proved most efficient as a lamb-marking dressing and as a dressing for struck sheep. This powder preparation is also used to protect freshly mulesed sheep and has been applied around rams' horns to prevent poll strike.

In America an interesting experiment has been reported on the systemic use of Ronnel to control the sheep blowfly. The drug was administered orally (150-200 mg./kg.) but the treatment was found to be effective only when the maggots were deep in the flesh and strikes were not cured. The treatment gave no residual effect against restrike. (Harquardt and Hawkins (1958)).

Nasal Bot (Oestrus ovis):

The effective removal of nasal bots from sheep is now possible using Neguvon drench at the dose rate of 50-60 mg./kg. in South Africa, a mixture of Neuvon and Asuntol at the ratio of 10:1 has also been used for this purpose, at a dose rate of 55 mg./kg. (Chavarria and Cavillo (1959), Stampa (1959)).

Sheep Tick (Ixodes ricinus)

Delnav (0.1%) has been used successfully in the United Kingdom to control the sheep tick.

HORSES:

Bots (Gastrophilus spp.):

Neguvon has proved most satisfactory for the removal of these parasites. The recommended dose is 30 mg./kg. (1½ grams/100 lbs.) with a maximum dose of 15 grams (½-oz.). It can be administered as a drench (5% solution) or mixed in the feed.

Other compounds that have been tested for this purpose are Ruelene, Narlene, Asuntol, Trolene and Dimethoale. All tended to be toxic at effective levels or else ineffective. (Drummond et al. (1959). Drudge et al. (1959)).

The toxicity of these insecticides to horses is reviewed in the paper by Jackson et al. (1960)

DOGS AND CATS:

Several of the organic phosphorus compounds have found a way into small animal practice, amongst which is malathion for the control of dog and cat fleas. It can be used as a 4% dust or as a 0.5% spray. Houses should be dusted with the 4% dust at the rate of 1-2 lbs. per 1,000 sq. ft. or sprayed at 0.5%, one gallon to 1,000 sq. ft. It has been noted that the organic phosphorus compounds may take up to 24 hours to kill the fleas, during which time they appear to be paralysed. Malathion appears relatively safe for use on both dogs and cats. Malathion has also been used to treat Otodectic mange as a spray (5%) or ointment (1%), as well as Notoedric mange of cats, as a 0.5% wash applied twice with a 7 to 8 day interval. (English (1960)). Ronnel has also been reported as a treatment for Demodectic mange in dogs. where seven topical treatments were given in 18 days using & 5% solution. At the same time a total of 6.5 gm. of the drug were given orally during this period. (McGregor and Lord (1959)).

POULTRY:

Lice and Mite Control:

Malathion has been reported as giving 100% kill and 14 weeks' protection against re-infestation of lice when used as a 4% dust at the rate of 1-1b. per 100 birds in either a dust-box or a natural wallow. (Rodriguez and Riehl (1960)). A similar period of freedom of mites was also given by Malathion when used as a dust blown into cracks, perches,etc. at the rate of 1-lb. of a 4% dust per 50-60 57. ft. or applied as a spray (0.5% -1%). Turkey lice have been effectively controlled by 1% malathion spray. In this case the wash was pumped at 60-lbs. pressure per sq. in. through an upturned boomspray forming a curtain through which the birds were driven. Gless and Raun (1958)).

PIGS:

Lice:

Malathion applied as a spray (0.6% - 1%) has been reported as giving complete control of this parasite for 30 days when applied to the pigs' pens and litter. Malathion appears to be relatively safe for use in pigs as no toxic reaction or irritation was seen in pigs on which 2 pints of wash with concentrations as high as 2% were applied.

Sarcoptic Mange:

Neguvon (50 mg./kg. orally) for three days, with a repeat treatment in 10 days, is reported as giving clinical cures of sarcoptic mange in pigs. (Armbrecht (1959)). Malathion has also been field tested for mange control in pigs. (Raun (1956)).

FLY CONTROL IN ANIMAL HOUSES:

Organic phosphorus compounds have proved most useful in the control of houseflies in animal premises. As sprays, Diazinon (0.5 - 1%) and Malathion (2 - 5%) have been used for application to walls, either with or without the inclusion of sugar as a bait (1-1b. per gallon of spray). The sugar solution should only be used on outside walls; manure heaps should be sprayed at weekly intervals and walls at monthly intervals. The use of impregnated cords strung to rafters, ceilings,etc. has proved effective. The cords may be soaked in either a Parathion/Xylene mixture (5-10%) or a Diazinon/Xylene mixture (25%). These have proved effective for up to 10 weeks. Dry or moist baits should also be placed on window sills or rafters, out of reach of children or animals, and for this purpose Neguvon or Diazinon may be used at the rate of 1 - 2% in sugar or molasses. (Pest Control (March, 1959)).

It is obvious, even from this brief summary, that the organic phosphorus compounds have a wide use in Veterinary Medicine and no doubt, many more will be developed before they have reached the limit of their usefulness. However, as resistance to Parathion, Malathion, Diazinon and Asuntol in houseflies and to Malathion in mosquitoes has been reported, at least some of our efforts should be aimed at discovering a new family or group of insecticides rather than relying for too long on the organic phosphorus compounds.

ORGANIC PHOSPHORUS COMPOUNDS

List of Common Names and Synonyms:—

PARATHION — Thiophos, E605, Folidol.

MALATHION — Malthon.

DIAZINON —

DELNAV — Hercules 528, AC.528.

NEGUVON — Bayer L13/59, Dipterex, Chlorophos, Tugor.

ASUNTOL — Bayer 21/199, Co-Ral, Coumaphos, Muscatox.

RONNEL — Dow ET-57, Trolene - Oral use, Korian - Spray use, Nankot - Spray use.

RUELENE — Dowco 132. Montrel.

NARLENE — Dowco 109.

DIMETHOATE — Rogor 40, American Cynamid 12880.

References:

  1. Armbrecht, G. (1959) — Vet. Bull., 29 (12): 690
  2. Chamberlain, W. F., Gatterdam, P. E. & Hopkins, D. E. (1960) — J. Econ. Ent., 53: 672
  3. Chavarria, C. M. & Carrillo, R. A. (1960) — Vet. Bull., 30 (9): 508
  4. Drudge, J. H., Leland, S. E., Wyant, Z. N. & Elam, G. W. (1959) — Journal of Parasitology, 45: 56
  5. Drummond, R. O. & Graham, O. H. (1959) — J. Econ. Ent., 52: 749
  6. Drummond, R. O., Jackson, J. B., Gless, E. E. & Moore, B. (1959) — Agric. Chem., 14 (12): 41
  7. Drummond, R. O., & Moore, B. (1960) — J. Econ, Ent., 53: 682
  8. English, P. B. (1960) — Aust. Vet. J., 36 (3): 85
  9. Gless, E. E. & Raun, E. S. (1958) — J. Econ. Ent., 51 (2): 229
  10. Jackson, J. B., Drummond, R. O., Buch, W. B. & Hunt, L. M. (1960) — J. Econ. Ent., 53: 602
  11. Kaplanis, J. N., Robbins, W. E., Darrow, D. L., Hopkins H. E., Monroe, R, E. & Treiber, C. (1959) — J. Econ. Ent., 52 (6): 1190
  12. Knapp, F. W., Terhaar, C. G. & Roan, C. C. (1958) — J. Econ. Ent., 51 (3): 361
  13. Krueger, H. R. & O'Brien, R. D. (1959) — J. Econ. Ent., 52 (6): 1063 - 1067
  14. March, K. B., Fukuto, T. R., Metcalf, R. L., Maxon, M. G. (1956) — J. Econ. Ent., 49 (2): 185
  15. Marquardt, W. C. & Hawkins, W. W. (1958) — J.A.V.M.A., 132 (10): 429
  16. McGregor, J. K. & Lord, L. H. (1959) — Vet. Med., 54: 308
  17. Murray, M. D. (1957) — Aust. Vet. J., 33 (5): 122
  18. Norris, K. R. (1957) — Aust. J. Agric. Res., 8: 768
  19. O'Brien, R. D. (1957) — J. Econ. Ent., 50 (2); 159 - 164
  20. O'Brien, R. D. & Wolfe, L. S. (1959) — J. Econ. Ent., 52 (4): 692
  21. Radeleff, R. D. & Woodard, G. T. (1957) — J.A.V.M.A., 130: 215
  22. Raun, E. S. (1956) — J. Econ. Ent., 49 (1): 140
  23. Rodriguez, T. L. & Riehl, L. A. (1960) — J. Econ. Ent., 53 (2): 328
  24. Roth, A, R. & Bigley, W. S. (1959) — J. Econ. Ent., 52 (3): 539
  25. Sharma, R, M., Dyal, R. S. & Chawla, L. R. (1960) — Vet. Rec., 72 (43): 898
  26. Sinclair, A. N. (1958) — Aust. Vet. J., 34 (12): 405
  27. Stampa, S. (1959) — J. S. Afr. Vet. Med. Ass., 30 (1): 19
  28. Winteringham, F. P. W. & Lewis, S. E. (1959) — Ann. Rev. Ent., 4: 303
  29. Wood, J. C., Malone, J. C., Sparrow, W. B. & Brown, P. R. M. (1959) — Vet. Rec.>, 71: 666
  30. Woodard, G. T. (1957) — Vet. Med., 52: 571
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