The Organophsphorus insecticides (or more commonly, the OP compounds) today account for approximately more than 35% of the registered Synthetic insecticides in the USA. In a strict sense OP compounds are compounds that inhibit cholinesterase, thus disrupting the nervous system. Parathion, malathaion, Diazinon and Dursban are few examples of OP. The usage of these chemicals in the agriculture and the residential areas alike has affected both the wild and domestic life alike. A vivid example is spraying in the heart of many residential neighborhoods in the western states with the insecticide Malathaion to deter insect infestation. Arizona and Southern California have witnessed a large scale of residential spraying during periods of high trapping for the Mediterranean and the Mexican Fruit fly. Pigeons can not escape the harm of these chemicals. The following cases illustrate the above explaining the mechanism of chemicals on the birds and finally how to treat them.
Case history 1:
A caller from Texas who received pigeons in the summer 1995 from another western state indicated that several of the received birds had seemed to be malnourished as evidenced by the thinness of the pectoral muscles. The pigeons were immediately placed on high protein content pellets made by Purina, that contained over 20% protein and contained all the essential minerals and vitamins required for the pigeons. The birds did seem to mind the pellets initially, then started to consume readily within couple of days and continued with good eating habits in the following weeks. Their natural behavior was normal displayed in mating, nest building, laying eggs and hatching some of them. In spite of that some of the birds continued on loosing weight and the newly hatching occasionally displayed twisted toes and leg deformation. The caller also indicated that he treated all the birds with the antibiotic baytril 5% in the drinking water accordingly. The source in Arizona had indicated to me a similar problem compounded by the demise of more than 20 birds in his loft. The self-prescribed baytril in the drinking water didn't help either in this case. The discussion has led both of us to believe that the episode took place as a result of a massive aerial insecticide spray that took place for several consecutive days in his area. The Arizona gentleman is residing in a middle of a beautiful orange grove and was not warned to take the proper precautions prior to the spraying.
Case history 2:
In September 1994, I noticed few ectoparasites on the primaries of few pigeons. For quick results, I opted to use Diazinon. A proper dilution was made up following the manufacture direction and two quick puffs were sprayed under the wings of all birds except for the breeders, which were housed in a separate loft. The following day many of the parasites were still alive. A second dilution was prepared, but this time it was made three times stronger. Spraying was done heavily to a degree of saturation on some birds. All the birds were let loose to dry in the sun.
Depending on the amount of dose, the length of exposure and the birds condition, there was an immediate and delayed reaction. Immediate reaction; starts within minutes of the exposure. Muscular twitching and muscularWeaknesses were noted. The birds could not walk steadily; others flew erratically rather than their usual tight kit. Others started to fall from the sky as if hit by a shotgun. Convulsion and death ensued. Lighter symptoms of the same reaction are parasympathetic in nature (e.g, bradycardia salivation and myosis). The saliva was thick and mucoidy and in turn plugging the bird's trachea causing it to suffocate on its own. Severe diarrhea was common among all, even the ones that were still acting normal. Over 10 dead birds were counted in spite of the proper emergency treatment.
Prolonged or long term reaction:
This stage occurs after a full recovery from the initial stage. Systemic effect: possible routes for the internalization of OP are by inhalation, Via the skin, Via the eggshell to affect the tissues of the embryo or via the gut if food or water became exposed. The role of the liver in the metabolism of these toxins is crucial because it possess a system whereby hydroxylation of the fat-soluble toxins renders them more water soluble for rapid excretion from the body. The importance of the liver as a site of metabolism is associated with the mixed function oxidase system.
The impact of OP on reproductive system
Widespread and deleterious effects covering all aspects of the reproductive process. These include retardation in the Oocyte formation and ovarian differentiation, decreased fecundity, decrease in the viability of the hatched eggs and impairment in the shell formation. Moreover, a significant route of excretion is via the eggs, apparently this is a general mechanism of excretion of lipophilic pollutants in birds. Thin eggshell is also noted and that is due to the inhibition of the enzyme carbolic anyhydrase. The enzyme is responsible for making calcium available to the eggshell in the oviduct. Further, they cause induction of enzymes in the liver responsible for the breakdown of Steroids hormones, depressing the level of blood Oestradiol and allowing as a consequence, the metabolization of bone calcium leading to bone deformation. In the above cases, each fancier involved had experienced a multiple of the above-mentioned complication. My pigeons unfortunately have experienced them all.
Biochemistry of the immediate reaction:
Cholinestrase is vital enzyme that destroys Acetylcholine, which is an undesirable by-product that builds up at the nerve endings. Thus, depriving the nerve impulses to be transmitted to the muscles. For that an animal that get afflicted by the poison manifests difficulty in muscle movement leading to convolution and paralysis depending on the severity of the case. The destruction or the hydrolysis of the Acetylcholine allows additional impulses to be transmitted to the muscle. The enzyme cholinesterase is found in red cells, lungs and spleen, in nerve endings and in the gray matter of the brain. A typical reaction of cholinesterase is as follows:
Cholinestrase Acetylcholine Bromide + H2O -----------à Choline Bromide + Acetate ion + Hydrogen
The most conspicuous feature of all OP compounds is that they mimic the gross molecular shape of the natural substrate of cholinesterase, acetylecholine.
Treatment and therapy:
Atropinization to block Acetylcholine action at the parasympathetic nerve endings and the central nervous system is the most widely prescribed medicine to both human and animals alike. Addition of daily grit and oyster shells to the main diet is essential to replenish the calcium deficiency. Antibiotics will render the matter worse and will exacerbate the situation for an already ailing liver. One of the characteristics of OP inhibition of cholinesterases is that the rate of recovery becomes less and less as the time of contact becomes longer.
Lehrman, interaction between internal and external environment
Physiological strategies in avian biology, Blakie
Toxicology of insecticides, Mastumura
Tietz of clinical chemistry, second edition
Meir, Avian endocrinology in chemical zoology