Viruses and rickettsiae are particles or chains of protein material which have the power to multiply. Most can only survive inside living animal or plant cells. They vary from 10-500 millionths of a millimeter in size (10-500 millimicrons), and unlike bacteria can pass through the pores of special unglazed, porcelain filters as used by virologists. New viruses are continually being discovered and there is little doubt that many more have yet to be classified. Of the dozen or so viral and related diseases of poultry, only four appear to be sufficiently common in other species of birds to warrant a full description here, namely, pox, ornithosis, Newcastle disease and Herpes virus infection of pigeons. The remaining diseases mentioned are either uncommon, found mainly in free-living birds, or are of doubtful identity or occurrence.
Pox or Avian Diptheria
Avian pox has been recognized as a distinct disease for centuries and has been a scourge wherever birds have been kept closely together. Avian pox viruses are akin to the pox diseases of man and other mammals. They produce the same type of lesion, although avian pox viruses do not generally affect mammals and vice versa. There appear to be several strains, the best known being those viruses infecting poultry, turkeys, pigeons, and passerines such as canaries. In the latter, pox is sometimes referred to as Kikuth's Disease. Most strains do not keep strictly to the species giving them their name and their virulence or disease-producing ability varies. Some strains are capable of becoming more virulent in an unusual host and less so in their normal host. This adaptability, however, is variable, and some strains may be completely unable to cause disease in an unnatural host species. The ability of pox viruses to stimulate the production of antibodies differs in the various species. In any bird where clinical illness is produced, infection is always followed by strong immunity or protection from further attacks in those which recover. Some strains, while causing little obvious disease, also produce immunity to one or more avian pox viruses. Most pigeon pox strains protect pigeons against both the pigeon and canary-type virus. Some strains capable of causing a high death rate in canaries will produce little evidence of disease and a high level of immunity in pigeons and poultry.
CLINICAL SIGNS: Pox primarily affects the skin and lining membranes of the head and its cavities. The virus grows in cells of the skin to such an extent that it destroys and bursts the cell, stimulating the production of lymph. The skin lesions start as vesicles or blisters of various sizes which separate the surface layers into pockets of watery fluid rich in multiplying virus. These swellings burst to the surface and the skin over them becomes yellow and necrotic, whilst the fluid or lymph congeals to form scabs. The scabs fuse together and may form a continuous crust or wart-like growths. Bacteria can now gain access and produce purulent discharges and further necrosis. These are particularly noticeable around the eyes where the exudate may cause the eyelids to adhere, producing blindness.
Conjunctivitis often occurs; it is manifested by a clear watery discharge from the eyes accompanied by congestion and oedema of the eyelids, giving them a puffy, half-closed appearance. The third eyelid is usually partly drawn across the eye. The face feathers become soiled. Sometimes a slight loss of activity or appetite occurs in the most seriously affected birds. In other respects the birds are normal. Within a few days several or all the birds may be affected. By then the earliest affected often have thickened, ocular discharge which may be sticky and mucoid or contain pus. The clear discharges are at first usually bacteriologically sterile but later become infected with bacteria such as Staphylococci or Escherichia coli. Lesions also occur near the nostrils, the angles of the beak and on any special structures, such as the cere, wattles and other fleshy parts. When the scabs fall off they may leave a scar. Canaries, pigeons and other affected birds also often show scabby lesions on the legs, feet and various parts of the body. In the mouth, throat and on other moist mucous surfaces, the lesions consist of white, moderately raised areas of sloughing, dead sheets of cells. This lifting up of the dead epithelium produces a so-called diphtheritic membrane, and the false membrane formed by coalescence of several such areas leaves a raw, red and eroded surface when the dead tissue is removed. Breathing may become difficult when throat lesions are present. In addition to these typical pox lesions, a generalized illness occurs caused by the presence of virus in the blood (i.e., a viraemia). The viraemia occurs early in the disease and can cause death. With certain strains of virus in some species, the viraemia has little or no effect on the bird. In severe cases of canary pox, however, the virus may multiply within the internal tissues, as well as the skin and mucosae. Clear exudates and sometimes hemorrhages are then seen at necropsy on the serous membranes lining the body cavity and the pericardium. Oedema of the lungs may also occur.
DIAGNOSIS: Although not the only disease in birds capable of causing extensive scab formation on the skin, false membranes in the mouth, illness and death, these signs are sufficient to warrant a suspicion of avian pox. The disease can only be accurately diagnosed using special laboratory tests. These involve the inoculation of virus-rich discharge into experimental birds or embryonated eggs, and successfully transmitting the disease. Microscopic and other examinations may also be necessary. When strongly suspected by your veterinarian, a program of vaccination (in those countries where suitable vaccines are available), isolation or culling can be undertaken on his advice. It is important to realize that the disease is contagious and also highly infectious and can exist in dried scabs for long periods.
DIFFERENTIAL DIAGNOSIS: Other diseases which can give rise to one or more of the signs of pox include:
1. Trichomoniasis (canker) of the mouth and throat. 2. Herpesvirus infection of pigeons. 3. Candidiasis (thrush, oidiomycosis, moniliasis). 4. Hypovitaminosis A (nutritional roup). 5. Ornithosis (ocular forms of the disease). 6. Knemidocoptic mange (scaly face). 7. Mosquito and other insect bites. 8. Favus (ringworm). 9. Some skin tumours. 10. Some local bacterial infections. 11. Some allergic reactions.TREATMENT AND PREVENTION: As with most viral infections, no drug has any direct effect on the virus, and prevention in the form of vaccination is probably the best means of control. There are breeders who claim successful treatment using flowers of sulphur, applied to skin lesions or given orally. Removal of skin lesions with sodium bicarbonate washes, careful removal of diphtheritic membranes in the mouth to prevent choking, and the raising of the environmental temperature to about 15-20°F (8-11°C) below blood heat will probably be equally effective. The main danger, however, with these manipulations is that they may spread the infection to other parts of the skin via the hands and utensils.
Bathing the eyes with 1-2 per cent saline solution followed by the application of a broad spectrum, antibiotic ointment containing chlortetracycline or oxytetracycline helps to combat conjunctivitis by eliminating bacteria. The infection, however, will run its course and usually clears up spontaneously, Nevertheless. bathing the eyes with a saline solution aids recovery, which may take at least a week. A crude method of vaccination, which may protect healthy birds which cannot be isolated from those infected, is to dip the tip of a sterile scalpel into a freshly ruptured and discharging sore of an affected bird, and with it scratch a small area of skin on the wing, back or legs of each healthy bird. The slow dispersal of the virus from the scarified area allows antibodies to develop without a general infection arising and before most of the birds have time to become naturally infected. If the disease is already incubating, this procedure will not give protection and may even actively aid the invasiveness of the disease. The decision whether or not to practice this method of vaccination should be left to the veterinarian, who may be able to suggest a commercial vaccine rather than the use of the homegrown virulent virus. Avian pox is most common in the temperate parts of the world and occurs mainly in the summer. Insects are probably responsible for some of the transmission from one premises to another, while wild birds can account for outbreaks spread over wider areas. Although primarily a contagious disease spread by direct contact, the survival of virus in scab particles, in feather debris and other substances, may result in infection via the mouth by contamination of food.
Ornithosis, Psittacosis or Parrot Fever
More info on Ornithosis & Psittacosis disease can be found in this article.
Probably more has been written about ornithosis than any other avian disease. It was first recognized and named in 1879. Because the disease is infectious and sometimes even fatal to human beings, the importation of psittacine species or parrot-like birds has been controlled in several countries as these species are especially susceptible to the infection. It was originally thought that a virus caused the infection, but it has now been established that the agent is a rickettsia-like organism, which is usually referred to as Bedsonia and more recently called Chlamydia. Ornithosis, which literally means "bird disease" started its recognized life with the names psittacosis and parrot fever, because it was originally believed that only parrots were affected. When the seriousness of human infection was realized and cases arose in people not in contact with parrots or budgerigars, investigations were carried out on numerous other species. It is now known that many species in a variety of families of birds and small mammals also carry the disease, often with little or no clinical signs in the creatures themselves. Although psittacine birds still appear to account for the greatest number of cases, ornithosis also occurs occasionally in domestic poultry, (especially in turkeys, ducks and pigeons), certain seabirds and some other species. In Britain ornithosis is now common in parrots and also in budgerigars.
The virulence of the disease varies from species to species and from outbreak to outbreak. Investigations in England, have shown that a high percentage of pigeons develop an immunity to the disease, while a smaller number harbour the ornithosis agent with little clinical effect. Human infections derived from pigeons appear to be less serious and less common than those contracted from parrots. It is possible that birds in the parrot family have the power of increasing the disease's virulence for man. Alternatively, more virulent strains may survive best in psittacines. The ornithosis agent is susceptible to some antibiotics, especially tetracyclines. It is of worldwide occurrence and is endemic in the bird population of many countries, as is shown by the detection of antibodies in the sera of many species. Only quite brief contact may be necessary for one bird to infect another or a human being. Transmission is by inspiration of the organism in water droplets or dust. A less common method of infection is via the mouth. Although showing no clinical signs of disease, many birds excrete the organism in the droppings or nasal discharges, while the feather dust and debris may also be contaminated. Repeated passages through a succession of individuals occasionally results in an intensification of the virulence for that species, until some birds show obvious signs of the disease and even die. The most commonly infected cage, aviary and ornamental birds are the psittacines, including the entire range of parrots, parrotlets, parakeets, budgerigars, macaws, cockatoos, cockatiels, lories, lorikeets and lovebirds, as well as all types of pigeons and doves. Gamebirds, including pheasants, partridges, certain ducks and also species of hummingbirds, magpies, tits, thrushes, various finches including the Java sparrow, canaries and cardinals, and some members of the troupial family are occasionally infected. No list can be complete because new host species are frequently being found.
CLINICAL SIGNS: Clinical signs of the disease include green or grey diarrhea, listlessness, huddling, closing of the eyes and conjunctivitis, droopiness, occasionally a watery or pus-like discharge from the nostrils and/or beak, rattling respiratory sounds, rapid labored breathing, lack of appetite, loss of weight, prostration and death. Flight is inhibited in older birds due to weakness and listlessness. Young stock are particularly susceptible. Intensively kept birds, such as those kept in large numbers in an aviary and bred collectively are most vulnerable to serious outbreaks. As with all diseases, the infection is less likely to occur in collections of birds where the hygiene is good and a balanced diet is fed. It is important to realize that birds which survive the disease may carry the causal organism for long periods, excreting it continuously or intermittently. These dangerous birds are called carriers, and may never show signs of illness. Although it is still not certain, it appears possible that some species can transmit the infection to the embryo by laying infected eggs. The shell may also become contaminated and infect the chick on hatching if the parent does its own brooding, or alternatively the adult may directly infect the nestlings.
When transported long distances, birds are often subjected to stresses such as change of diet, fluctuating temperatures and restricted activity caused by overcrowding in cramped containers. Adverse conditions of this nature frequently lower the birds' resistance to disease and especially to ornithosis. The survivors, however, reach the dealers and pet shops, where, when weak and therefore tame, they may be sold by unscrupulous people to unsuspecting members of the public. Under such circumstances the disease often becomes virulent for man and other avian species. The isolated parrot imported by a seaman for his family and kept under good conditions usually becomes acclimatized by the time he gets it home, and if by then it is still healthy, it is likely to remain so. It may still, however, be a carrier and a potential source of infection to its owner or any other birds with which it comes into contact.
DIAGNOSIS: It will be appreciated from what has been said that clinical signs are far from specific or diagnostic, although in typical cases the post-mortem lesions are fairly characteristic. The disease may be suspected from the pattern of infection in an area or premises. Confirmation, however, requires highly specialized laboratory techniques. One method is serological testing for antibodies of the disease. This is the usual method when human beings are involved. It is merely a method of measuring the amount of resistance the man or bird has developed in response to meeting the disease. If this happened a long time ago, the antibody level will be low. When the disease is being actively fought, however, the level rises rapidly. A fairly recent infection produces a high level of antibodies which only falls slowly over months or years. Other stages such as complete recovery, the carrier state, or lack of adequate antibody response to infection all give inconclusive results. The presence of the infection in a bird can only be demonstrated with certainty after death by infecting a susceptible host, such as a mouse. This involves inoculating an extract of a piece of diseased liver, spleen or other internal organ into the brain or peritoneal cavity. Death of a proportion of inoculated mice showing certain characteristic lesions confirms the diagnosis. The disease can also be diagnosed by inoculation of the extracts into the yolk sacs of living embryonated eggs.
TREATMENT: Infected birds used to be destroyed. A while ago it was unwise to attempt treatment unless the dangers of the situation are appreciated and the premises and stock are self-contained. Treatment should be carried out only under the strict supervision of a veterinarian. The owner should not underestimate the considerable danger to himself, his family and others who may come into close contact with his birds or himself. There are medicines available today from most vets to treat this today. The tetracyclines are the best drugs where treatment is thought prudent. They check, but do not necessarily kill the causal organism. Symptomatic treatment and careful nursing should accompany the specific antibiotic therapy.
Newcastle Disease (Fowl Pest)
This is a highly infectious and serious disease of poultry, being virtually world-wide in distribution. It is commonly called "fowl pest" in Great Britain, although this term also includes a similar viral infection of poultry more correctly known as "fowl plague". In some countries the disease in poultry is notifiable and if suspected it must be reported, so that the official veterinary officers can take steps to control the spread of infection. Many species are susceptible to the disease, but it occurs mainly in gallinaceous birds such as pheasants, partridges and quail, and birds of prey including owls, pigeons and psittacines. Except for recently imported parrots and other psittacines, which have undergone various stresses, most species usually become infected from poultry, particularly chickens. In the majority of species young birds are probably more susceptible than adults.
CLINICAL SIGNS: Signs shown by pheasants, partridges and other game birds are similar to those seen in the domestic fowl. They vary according to the virulence of the virus but include difficulty in breathing with discharge from the nostrils, greenish or yellowish diarrhoea, tremors and paralysis of the legs and wings. Sometimes there is loss of balance and usually depression and ruffled feathers. Birds of prey may exhibit head shaking and sneezing, whilst pigeons show nervous rather than respiratory signs. In some species or when relatively mild strains of virus are involved, the signs may be vague, birds showing little more than depression and ruffled feathers. In most species the infection is likely to be acute, birds dying within a few days of showing signs of illness.
DIAGNOSIS: Whenever deaths occur in birds which are in close proximity to confirmed outbreaks of the infection in poultry, the disease should be suspected immediately. Although in some species the clinical signs may denote the possibility of the infection, it is not possible to confirm the disease without a proper post-mortem examination, including isolation and identification of the virus. The demonstration of antibodies to the disease in blood samples taken from live birds is also an important aid to diagnosis.
TREATMENT AND PREVENTION: There is no sure treatment available. Prevention of the disease is important. Birds should be kept well away from domestic poultry, especially as the virus is capable of surviving for long periods under favorable conditions of temperature and humidity. All recently acquired birds, especially recently imported psittacines, should be kept in strict isolation for about a month, before being introduced to a collection. Ideally this means that they should be kept on different premises and cared for by a person who has no contact with other birds. Day-old chicks, raw poultry meat and feathers should never be used for feeding carnivorous species such as birds of prey, because they may be contaminated and are therefore a dangerous potential source of the virus. The infection is also easily transmitted to other birds via excreta and nasal exudates.
Vaccines are available for gallinaceous birds such as the domestic fowl. The vaccines may be either "live" or "dead", that is containing living or artificially inactivated virus. Both types of vaccine afford protection from the disease for only short periods of time. Although the "live" vaccines contain only mildly virulent strains of virus, their use should be confined to gallinaceous birds, because they may be fatal to many other species. Although there is little information available regarding the value of vaccination for birds other than poultry, there is some indication that it may help to protect birds of prey from the disease. The types of vaccines available vary in different countries and a veterinarian should always be consulted for advice regarding their use.
Herpesvirus, Smadel's Viral Infection (One-eyed Roup or Ophthalmia)
The clinical signs shown by racing pigeons infected with Herpes virus or ornithosis are similar and impossible to diagnose in these birds without laboratory examination. It follows therefore that the diseases, known by pigeon breeders as roup, ophthalmia or "eye-colds", may be either of these diseases or indeed Mycoplasma infections.
CLINICAL SIGNS: Birds under a year old are mostly affected. Watery eye discharge indicating a conjunctivitis and nasal discharge due to rhinitis or inflammation of the nasal passages, are almost constant features of the disease, and some may also show respiratory distress caused by the mucous membrane of the larynx being coated by a diphtheritic membrane. Small ulcers and yellowish-brown cheesy material may be present in the pharynx, larynx and oesophagus, and tracheitis or inflammation of the trachea is sometimes present. Without microscopical and other laboratory diagnostic methods the mouth and oesophageal lesions are indistinguishable from trichomoniasis. Lesions in the internal organs include hepatitis and nephritis.
TREATMENT: There is no sure specific treatment for the virus itself and in the absence of a confirmatory laboratory diagnosis, cases should be treated as recommended for ornithosis, Mycoplasma infection or trichomoniasis, depending upon the circumstances.
Other Viral Infections
It is not within the scope of this article to deal with all the other viral infections which may be met in birds. Textbooks on poultry diseases should be consulted for information on infectious laryngotracheitis, infectious bronchitis, encephalomyelitis (epidemic tremor), fowl plague, the lymphoid leukosis complex including Marek's disease, avian monocytosis and infectious synovitis. All of these are virtually confined to the domestic fowl, although infectious laryngotracheitis has been diagnosed in pheasants, and fowl plague in waterfowl. Books on poultry diseases should also be consulted for information on viral diseases of waterfowl: duck plague or duck virus enteritis and duck virus hepatitis. Several species of seabirds become infected with a virus known as puffinosis or vesicular dermatitis. Quail bronchitis is mainly confined to game-bird farms in North America. Lesser known viral infections of non-domesticated species of birds include rabies, viral hepatosplenitis of owls, Pacheco's parrot disease, avian influenza and a "virus hepatitis". Perhaps least is known about the last mentioned infection. Aegyptianellosis, which is probably a rickettsial infection although previously believed to be due to protozoa, is mainly a disease of geese and the domestic fowl.
Many species of free-flying birds carry viruses belonging to the arthropod-borne encephalitides. Some of these so-called arboviruses are important infections of man and domestic mammals, but they seldom seem to be responsible for clinical disease in birds. It can be stated categorically that poliomyelitis virus is not a natural inhabitant of avian tissues. The observation which eventually reached the newspapers a few years ago concerning the isolation of the virus from a budgerigar and the presence of antibodies to poliomyelitis virus in serum from one of these birds merely indicated contamination with the virus from an infected human contact. No evidence could be found that this or other individuals of the species were truly susceptible to the disease.
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