Zoonotic diseases and wildlife
Compiled, & shared by-DR. RAJESH KUMAR SINGH, (LIVESTOCK & POULTRY CONSULTANT), JAMSHEDPUR Post no 1385Dt 03/09//2019
JHARKHAND,INDIA 9431309542, rajeshsinghvet@gmail.com
Zoonotic infections are diseases that occur primarily in wild and domestic animals that can be transmitted to humans. Infectious pathogens that originate in wildlife have become increasingly important in recent decades.The emergence and reemergence of these wildlife zoonoses are associated with a range of casual factors, most of them as a result of human activities such as increasing human populations, global human travel and trade of wildlife, changing land-use patterns, and other environmental changes. Veterinarians are often considered a source of information by the general public as well as clients on all topics relating to animal health and zoonotic diseases. Although all persons who feel they have been exposed to a zoonotic pathogen should be immediately referred to his or her health care provider so that a diagnosis can be made and the correct treatment prescribed, it is important that veterinarians are able to give advice regarding the potential risks and what to do in the event of exposure, assist in early recognition of disease, as well as provide information to help prevent exposure.
Zoos and biological parks are considered as a hub for public recreation and education. This is highlighted by the fact that visitors to the zoos are increasing year by year and they generate sizeable revenue. Veterinary professionals play a pivotal role in health management of wild animals in zoos and biological parks. Since veterinarians work in close contact with wild animals, there is a potential risk of transmission of zoonotic diseases from wild animals to humans and vice versa. There are approximately 1415 infectious agents causing diseases in humans, out of which 868 (61%) are known to be zoonotic in nature. It is also important to note that more than 70% of the emerging zoonotic diseases have wild animals as reservoir hosts. The major zoonotic diseases that are transmitted from wild animals to humans include rabies, anthrax, leptospirosis, Q-fever, psittacosis, hendra virus, nipah virus, herpes B encephalitis, toxoplasmosis, etc. Hence, it is imperative for veterinarians and zoo staff to be fully aware of the knowledge pertaining to the source, transmission, pathogenicity, treatment and control of zoonotic diseases.
Diseases of wildlife can cause significant illness and death to individual animals and
can significantly affect wildlife populations. Wildlife species can also serve as natural hosts for certain diseases that affect humans (zoonoses). The disease agents or parasites that cause these zoonotic diseases can be contracted from wildlife directly by bites or contamination, or indirectly through the bite of arthropod vectors such as mosquitoes, ticks, fleas, and mites that have previously fed on an infected animal. These zoonotic diseases are
primarily diseases acquired within a specific locality, and secondarily, diseases of occupation
and avocation. Biologists, field assistants, hunters, and other individuals who work directly with wildlife have an increased risk of acquiring these diseases directly from animal hosts or their ectoparasites. Plague, tularemia, and leptospirosis have been acquired in the handling and skinning of rodents, rabbits, and carnivores. Humans have usually acquired diseases like
Colorado tick fever, Rocky Mountain spotted fever, and Lyme disease because they have spent time in optimal habitats of disease vectors and hosts. Therefore, some general precautions should be taken to reduce risks of exposure and prevent infection.
Zoonotic diseases, a global threat —-
The increase in the incidence of zoonoses, to a significant extent, is a reflection of the change in our interactions with our forest ecosystems. The development of agriculture brought an end to an exclusive hunter-gatherer way of life. Despite the fact that today there are no known populations that live purely as hunter-gatherers, it is reported that in 62 developing countries, people obtain more than 20 per cent of their nutrition through wild meat and fish. Populations living in and around forests also depend to a great extent on the forests as a source of livelihood. Nevertheless, the need for food drove the development of agriculture, which altered landscapes and populations. This changed the nature of human contact with forests.
India is particularly vulnerable to many forest-originated diseases. Some 2,474 villages are inside India’s forests, while some 170,000 villages are around forest areas. More to it, 220 million people depend on forestry for survival. This means a significant number of people interact with forest in their day to day lives. India’s poorest also reside in the forested areas thus having less economic capacity to fight disease outbreaks. In these areas, public health facilities are sparse and most of the residents have to travel long to access them (see ‘Fallout of development’,).
The recent upsurge in the incidence of infectious diseases and zoonoses has often been attributed to the dramatic increase in population, mobility and the associated social and environmental changes in the past 70 years. However, as Colin D Butler, professor of public health at the University of Canberra in Australia, says, “The harm to human health and wellbeing caused by forest clearance is often disguised by scale, time and the socioeconomic and cultural distance between the policy-makers whose decisions facilitate forest clearance and those who suffer.”
Research shows that changes in land use, including deforestation and forest fragmentation, urbanisation and intensification of agriculture, have contributed greatly to the rise in the incidence of infectious diseases. “Indeed the current increase coincides with accelerating rates of tropical deforestation in the past several decades. Today, both deforestation and emerging infectious diseases remain largely associated with tropical regions but have impacts that extend globally,” states a paper in Unasylva, a journal of forestry and forest industries published by the Food and Agriculture Organization (FAO). As mentioned earlier, about three-fourths of all infectious diseases have, at some point, been contracted from animals. There are about 250 EIDs, about 15 per cent of which currently show a direct association with forests. Some EIDs were originally transmitted from animals to humans but have now escaped the sylvatic cycle, where the pathogen spends some time in an animal before being transmitted. These diseases have adapted to a human-sustained cycle independent of forests.
Destroying nature unleashes viruses
The diseases currently associated with forests can, in several ways, be seen as a reaction to change in the relationship between humans and forests. Changes in forest cover and land use increase human contact with pathogens that were earlier contained within forests (see ‘How deforestation impacts health’, p41). The impact of such pathogens is exacerbated in the case of migrant and alien populations that lack previous exposure. A rapid increase in population provides a ready pool of hosts for pathogens and enables adaptation.
Faustian bargain
As much as the pathogen and vector ecology is responsible for zoonotic diseases, changes in human ecology are responsible for the speed of transmission and the global scope many diseases have recently acquired. Construction of roads and dams in recently cleared forest areas and rapid urbanisation often bring people, especially migrant populations that are immunologically naïve, in close contact with pathogens. The spread and persistence of chikungunya serves as a classic example of how immunologically naïve populations can sustain an infectious disease .
General precautions
Use extreme caution when approaching or handling a wild animal that looks sick or abnormal to guard against those diseases contracted directly from wildlife. Procedures for basic personal hygiene and cleanliness of equipment are important for any activity but become a matter of major health concern when handling animals or their products that could be infected with disease agents. Some of the important precautions are: ———–
• Wear protective clothing, particularly disposable rubber or plastic gloves, when dissecting or skinning wild animals.
• Scrub the work area, knives, other tools, and reusable gloves with soap or detergent followed by disinfection with diluted household bleach.
• Avoid eating and drinking while handling or skinning animals and wash hands thoroughly when finished.
• Safely dispose of carcasses and tissues as well as any contaminated disposable items like plastic gloves.
• Contact a physician if you become sick following exposure to a wild animal or its ectoparasites. Inform the physician of your possible exposure to a zoonotic disease.
Precautions against acquiring fungal diseases, especially histoplasmosis, should be taken when working in high-risk sites that contain contaminated soil or accumulations of animal feces; for example, under large bird roosts or in buildings or caves containing bat colonies. Wear protective masks to reduce or prevent the inhalation of fungal spores.
Protection from vector-borne diseases in high-risk areas involves personal measures such
as using mosquito or tick repellents, wearing special clothing, or simply tucking pant cuffs into
socks to increase the chance of finding crawling ticks before they attach. Additional preventive
methods include checking your clothing and body and your pets for ticks and removing the ticks
promptly after returning from infested sites. If possible, avoid tick-in-fested areas or locations
with intense mosquito activity during the transmission season. Reduce outdoor exposure to
mosquitoes especially in early evening hours to diminish the risk of infection with mosquito- borne diseases.
Equally important preventive measures are knowledge of the diseases present in the general area and the specific habitats and times of year that present the greatest risk of exposure. Knowledge of and recognition of the early symptoms of the diseases and the conditions of exposure are essential in preventing severe illness.
Also important are medical evaluation and treatment with proper antibiotics. For example, if you become ill following some field activity in a known plague-endemic area and you recognize the early symptoms of the disease, seeking medical care and informing the attending physician of your possible exposure to plague will aid in the correct treatment of your illness and reduce the risk of complications or even death.
In addition to taking personal precautions, risk of acquiring vector-borne diseases can be reduced in specific locations through area-wide applications of insecticides to control mosquito or flea vectors or acaricides to control tick vectors. Reduction in host populations (for example, rodents) and their ectoparasites (fleas or ticks) may be needed to control transmission of such
diseases as plague or Lyme disease. Vaccination of wildlife hosts as a means of reducing zoonotic diseases is currently being investigated and may soon be available for diseases like rabies.
Directly Transmitted Diseases
Rabies
Rabies is an acute disease, caused by a virus (Rhabdovirus) that can infect all warmblooded animals, and is usually fatal. Certain carnivorous mammals and bats are the usual animal hosts. Rabies occurs throughout most of the world; only Australia and Antarctica are free of it. Most human cases have been contracted from rabies-infected dogs. Most of the treatments are still due to dog and cat bites; however, these pet species have the lowest occurrence of reported rabies among all animal species tested.
Rabies is considered almost 100% fatal once clinical signs develop. The disease progresses rapidly following the appearance of clinical signs, and the animal dies within a few days. Although abnormal behavior is not diagnostic for rabies (other diseases, like distemper, cause similar behavioral changes), atypical behavior and signs develop following brain infection, and rabies should be suspected whenever wild animals display unusual behavior.
Infected animals usually display either “furious” or “dumb” rabies, although some animals progress through both stages. Skunks, raccoons, foxes, and other canids usually have furious rabies and are unduly aggressive before convulsions and paralysis set in. Some animals, however, have dumb rabies and proceed to tremors and convulsions without agitation or aggression. Other behavioral changes include friendliness or loss of fear, appearance in the
daytime for some typically nocturnal species (skunks, bats), unprovoked attacks on anything that moves (including inanimate objects), bewilderment, and aimless wandering. Unusual barking, crying, and frothing at the mouth are additional signs, which are the result of paralysis of the throat muscles. Occasionally, rabid bats are encountered prostrate or fluttering on the ground,
unable to fly; they should be handled with care because they can still bite and transmit rabies.
Some rabid bats, particularly solitary species like the hoary bat, are aggressive and have been
known to attack people. In domestic animals, rabies should be suspected if there is any change in normal habits, such as sudden change in disposition, failure to eat or drink, running into objects, or paralysis.
Rabies virus is transmitted primarily via the saliva during the bite of a rabid animal.
However, other methods of transmission are possible. Accidental exposure of wounds or cuts to
the saliva or tissues of infected animals can occur. The virus is also present in various body
organs of infected animals, especially the brain and salivary glands, which poses a health hazard
to persons who are field dressing or performing necropsies on these animals. In addition, aerosol exposure has occurred, although rarely, in caves containing very large populations of infected bats. Transmission between animals also occurs by ingestion of infected tissues and by transplacental passage to offspring.
Use caution when approaching a suspected rabid animal since many are still aggressive and can bite even if paralyzed. If the animal is still alive, it should be killed humanely without damaging the head. To confirm whether an animal is infected with rabies, the animal must be submitted to the local health department or state diagnostic laboratory for testing.
Avoid exposure to any sick or dead animals that are suspected to have rabies. Handle any dead animal with gloves or with a plastic bag that can be turned inside-out to cover and contain the animal. Avoid direct skin contact with the animal. For large animals such as skunks and raccoons, remove the head cautiously and seal it in a plastic bag, avoiding contact or aerosol exposure. Seal the whole animal or head inside an additional plastic bag (double) and keep it cool at all times. Do not freeze the specimen unless a delay of several days is anticipated before it is examined for rabies. Disinfect gloves or knives that were in contact with the animal with a strong detergent or bleach or dispose of them.
For transport to the laboratory, place the double-wrapped specimen in a leak-proof container with a coolant (not wet ice). Send the container by bus or other prearranged transportation. Include information about the specimen (species, date, geographic data and behavior) and the names, addresses, and telephone numbers of the person submitting the specimen and of anyone exposed to the animal.
To test for rabies, a fluorescent antibody test (FAT) is performed directly on brain tissue to distinguish rabies virus from other disease agents (like distemper virus) that could be present in the animal’s brain. In some states, brain material is inoculated into mice to demonstrate virus for those specimens that resulted in human exposure.
If a person or pet is exposed to an animal suspected of having rabies but that has not been captured, record a description of the suspect animal (species, behavior) and provide the description to public health officials or the attending physician to determine possible treatment.
Prevention and treatment:
The best treatment for rabies is prevention. Individuals at high risk of exposure to rabies, such as wildlife biologists, game wardens, animal control officers, animal handlers, and veterinarians should be vaccinated before potential exposure. Safe and highly effective vaccines are available through a physician or the local health department.
First aid should immediately be provided to a person who has been bitten by or had
contact with a potentially rabid animal. Scrub the exposed site, including bite wounds, with soap and water or water alone and flush thoroughly. Then apply a strong first aid solution (iodine) or cream. First aid treatment is the most effective method of preventing infection by the rabies virus
but should not preclude medical attention from a physician, hospital emergency room, or the
local health department. Contact your physician or health department as soon as possible to determine dosage of rabies vaccine and whether antirabies serum is required. Inform the health care professionals about the rabid animal and the circumstances of the exposure (species of animal involved and its behavior, if the attack or bite from the animal was provoked, and what
type of first aid was administered).
Tuberculosis
Tuberculosis (TB), considered an important emerging disease in humans and domesticate animal but now a days, it is also become important for wildlife. Although Mycobacterium tuberculosis is the most common infection in humans, M. bovis is responsible for an increasing
proportion of human TB cases. M. bovis is widespread in domestic animals and has been
extensively documented in both captive and free-ranging wildlife populations. A number of
wildlife populations are endemically infected, for example, the European badger (Meles meles) in the United Kingdom, the African buffalo (Syncerus caffer) in South Africa, Spotted deer, Nilgai and other different species of deer and antelopes. These permanent reservoirs of infection
pose a serious threat to public health and TB eradication programs. Necessary precautions need to be taken when there are possibilities of disease being found in the wildlife population.
Trichinosis
Trichinosis may result in diarrhea, sudden edema of the upper eyelids, photophobia, muscle soreness and pain, skin lesions, thirst, sweating, chills, and weakness. Other respiratory and neurological symptoms may appear if treatment is delayed. Trichinosis is contracted by eating infected meat which contains the encysted parasites. The parasites may remain infectious in meat which is raw or poorly cooked. Trichinosis is caused by a nematode parasite which produces the disease in humans and domestic and wild animals. Evidence indicates that nearly all mammals are susceptible to infections with this parasite, which encysts in the muscle of the host and is then transmitted through consumption of infected flesh. As would be expected, the disease is most common in wild carnivores and scavengers.
As with other wildlife diseases, trichinosis is difficult to control in nature. However, certain steps can be taken to decrease the problem. Carcasses of carnivores and other meat-eating species should not be discarded in the fields or woods, but should be made unavailable by burying or other means. These carcasses also should not be fed to swine, dogs, or other domestic
animals. Open garbage dumps should be replaced by the landfill type or other methods of
disposal where wildlife will not have access to meat scraps. If open garbage dumps cannot be
eliminated, rodent control programs should be initiated and the areas fenced to prevent scavenging by larger animals such as foxes. These steps would markedly reduce the problem of trichinosis in wildlife in the United States.
If carnivorous or omnivorous wildlife such as bears, bobcats, opossums, raccoons, or feral pigs are consumed by humans, the meat should be properly prepared by cooking, freezing, or curing to destroy any viable trichinae. Cooking to an internal temperature of 137°F is deemed sufficient for pork, while freezing at 5°F for 20 days, -10°F for 10 days, or 20°F for 6 days will kill trichinae. Curing should follow approved government regulations.
Tick-borne Diseases:
Rocky Mountain spotted fever (Tick-borne Typhus)
Rocky Mountain spotted fever (RMSF) is a moderate to severe illness caused by a rickettsia (Rickettsia rickettsii). The disease is distinguished by a sudden onset of high fever, severe headache, muscle pain, and a red rash starting on the extremities about 3 to 6 days after onset of symptoms and extending to the palms of hands and soles of feet and then to the rest of the body. Delirium, coma, and death occur in about 1% to 2% of cases (15% to 20% in untreated cases). The disease is transmitted to humans in by several hard tick (Ixodidae) species; D. andersoni in the Rocky Mountain region, D. variabilis in the east and southeast, and Amblyomma americanum in the south-central states. The natural hosts for the rickettsia are a variety of wild rodents, although rabbits and wild and domestic carnivores are involved in some cases. The rickettsia survive the winter months in the tick vector and may be maintained by transovarial transmission from the female adult tick to its offspring.
Avoid tick-infested areas and use personal measures to protect against tick bites. No vaccine is presently licensed for public use, but antibiotic treatment is effective and should be initiated without waiting for laboratory confirmation of clinical diagnosis.
Lyme Disease
Lyme disease is caused by a spirochete bacterium (Borrelia burgdorferi) that is
transmitted to humans by hard ticks. Early symptoms include a flu-like illness with headache,
slight fever, muscle or joint pain, neck stiffness, swollen glands, jaw discomfort, and
inflammation of the eye membranes. A diagnostic rash, erythema migrans (EM), occurs in 65% to 75% of the cases. The rapidly expanding red rash starts at the tick bite site and expands to a
nearly circular lesion of about 1 to 8 inches (2 to 20 cm). It often has a bulls-eye appearance with central clearing and/or darkening around the edge. Additional smaller skin lesions may appear at other sites of the body and may last for days or weeks. Later symptoms, including heart, nervous system, and joint manifestations, may develop in untreated individuals. The joint pain and swelling usually occur one or more months after infection, may involve one or more joints, and
may recur in different joints; the knee joint is most frequently affected. Domestic animals may be affected as well.
Flea-borne
Diseases
Plague
Plague is an acute disease caused by the bacteria Yersinia pestis. Humans usually become infected by the bites of infected fleas but also directly from exposure to tissues or body fluids
from diseased animals, especially when skinning animals. The disease is characterized by the
sudden onset of fever and chills, followed by the development of swollen and painful lymph
nodes (buboes) in the armpits, groin, and other areas 2 to 6 days following exposure. In addition to the bubonic form, septicemic infection may develop and involve other organs. Secondary infection of the lungs may lead to primary plague pneumonia, which then can be transmitted from person to person by aerosol. The disease may be only mild and short-lived but frequently
progresses to a severe form, with 25% to 60% fatality in untreated cases. Plague is maintained in wild rodent populations in the western states by flea transmission between rodents. Sylvatic plague may persist in these animal populations with varying severity, depending on the species’ resistance. Rabbits, hares, carnivores, and wild ungulates have also been infected occasionally. Use insect repellents on skin or treat field clothes with permethrin. Practice good sanitation procedures when handling animals. Seek medical care and treatment if sick.
Murine Typhus Fever
Murine typhus fever is caused by Rickettsia typhi, a rickettsial organism that occurs throughout the world. Rats are the reservoir animals from which the disease reaches many humans by way of rat fleas. The oriental rat flea, Xenopsylla cheopis, is considered the most important vector of the disease. The causative organism enters the bloodstream when feces of infected fleas are scratched or rubbed into a flea-bite wound or other breaks in the skin. Murine typhus is similar to epidemic or louse-borne typhus, but illness is much milder and the fatality rate in untreated cases is much lower.
Commensal Rodent-borne Diseases
Rats and mice are responsible for the spread of over 35 diseases, either directly, through contamination of human food with their urine or feces, or indirectly, by way of rodent fleas and mites. Following are brief descriptions of the more common of these diseases.
Rat-bite Fever
Rat-bite fever is caused by the bacteria Streptobacillus moniliformis, which is found on the teeth and gums of rats. It is transferred from rats to humans by the bite of the rat. The most frequently occurring rat-bite fever in the United States is called Haverhill fever. It is similar to the rat-bite fever of the Orient called sodoku (caused by Spirillus minus).
Leptospirosis (Weil’s Disease)
Leptospirosis is a mild to severe infection that is seldom fatal. Human cases of the
disease result from direct or indirect contact with infected urine of rodents and other animals. The spirochetes (Leptospira spp., primarily L. icterohemorrhagiae) are found in contaminated water or on food, and may enter humans through mucous membranes or minute cuts or abrasions
of the skin. Thus, Weil’s disease is often found in sailors, miners, sewer workers, and fish or
poultry dealers.
Symptoms of leptospirosis infection range from none to severe, with acute fatalities. Many infections are characterized by diarrhea, chills, vomiting, myalgia, and kidney damage. Prevention is the most important means of dealing with this disease. Proper sanitation, rodent-
proofing, and food storage and handling are essential. Medical attention is typically required.
Salmonellosis
The Salmonella group of bacteria exists nearly everywhere in the environment and, unfortunately, several serotypes are pathogenic to humans and other animals. Salmonellosis can lead to severe cases of gastroenteritis (food poisoning), enteric fever septicemia (blood poisoning), and death. Food poisoning, the most common malady, is characterized by a sudden onset of abdominal pain, diahrrea, nausea, and vomiting. Due to the severity of this disease, medical attention is typically required.
Salmonella bacteria recognize few host barriers and are transmitted in many ways. One common form of transmission is through food contaminated by rat or mouse feces that contain Salmonella (especially S. typhimurium) organisms. It may also be spread by birds, which contaminate food with their feces or bacteria carried on their feet.
As with leptospirosis, the most important means of reducing the potential of this disease is through proper sanitation, rodent-proofing, and food storage and handling. Rodent control through trapping and appropriate use of toxicants may also be necessary.
Bird-borne Diseases
Large roosting concentrations of birds can be noisy, and the associated droppings can be a nuisance because of the objectionable odor and mess. In addition, birds may carry and transmit diseases to livestock and humans. Collections of droppings may provide a medium for bacterial and fungal growth that could pose a potential public health problem. Birds should be dispersed or controlled when they form large concentrations near human habitations and are judged to pose a threat to public health or livestock. Concentrations of birds that do not threaten human health or agriculture are usually better left undisturbed.
Avian Influenza
Avian Influenza (AI) is a viral disease that affects the respiratory and digestive systems of most species of domestic and wild birds. AI is characterized into two basic forms:
High Pathogenicity Avian Influenza (HPAI) – a rapidly fatal form of AI among birds, and Low
Pathogenicity Avian Influenza (LPAI) – a mild, often undetected form of the disease that
frequently occurs in wild bird populations. H5N1 Surface proteins on avian influenza viruses are
classified as H – Hemagglutinin and N – Neuraminidase. There are 16 H and 9 N types affecting birds. The possible combinations of H & N surface proteins create the numerous strains of AI
such as the Asian HPAI H5N1 currently affecting poultry, people and some wild birds in Europe, Africa and Asia. H5N1 is a form of HPAI, however, not all H5N1 avian viruses are HPAI. All birds are susceptible. Waterfowl, shorebirds, marine birds and upland game birds are known carriers of the LPAI form of avian influenza. AI is passed between birds through fecal material and body fluids such as saliva, nasal secretions and aerosol droplets. In Southeast Asia poultry may have spread HPAI to wild birds through contact with domestic chickens, ducks and geese
raised outdoors. Avian Influenza has not been transmitted from wild birds to humans. The
current outbreaks in Asia, Europe and Africa are between captive poultry and people. Since 2003 approximately 250 individuals have been affected with the Asian HPAI H5N1 strain of the influenza virus causing mortality in about half of these people. In the current outbreaks in Eurasia, human-to-human transmission has not been documented. Previous worldwide human pandemic flu outbreaks, such as the one in 1918 involved human-to-human transmission and killed millions of people.
Histoplasmosis
Histoplasmosis is a respiratory disease in humans caused by inhaling spores from the fungus Histoplasma capsulatum. Birds do not spread the disease directly — spores are spread by the wind and the disease is contracted by inhalation. Bird droppings enrich the soil and promote growth of the fungus. Notable sources for histoplasmosis infection include: (1) traditional bird roosts, (2) poultry farms, (3) enclosed buildings where birds or bats have roosted, and (4) natural
or organic fertilizers. In addition, the fungus can grow in various natural soils, with or without droppings.
Infection by only a few spores generally produces a mild case in humans and people are often unaware that they have contracted the disease (unless it is detected later through a skin reactivity test or lung X ray that reveals healed lesions). A more severe infection may result in an
acute respiratory illness with flu-like symptoms (in fact, histoplasmosis is often misdiagnosed as flu). The most serious infections, usually resulting from massive spore inhalation, may involve a dissemination of the fungus through the blood stream. Such cases may become chronic, recurring at later times, and affect organs other than the lungs. Treatment with an antifungal agent such as
amphotericin B or imidazole ketoconazole may be prescribed in more severe cases.
Not all blackbird or starling roosts pose immediate public health problems related to histoplasmosis. The histoplasmosis fungus grows readily in the soil beneath bird roosts, but it cannot form spores under the acidic conditions of fresh droppings. An active, undisturbed roost may only give off a few spores. Old or abandoned roosts, however, can pose a significant threat
to human health. After the droppings have dried out or been leached by the rain, the right
conditions develop for spore release. If the soil is stirred up under dusty conditions, as may be
the case in land clearing or bulldozing, massive amounts of spores may be released. Severe
epidemics have occurred in association with bird roosts under such conditions.
Birds in large roosts can be dispersed by the use of various frightening devices or by roost thinning or clearing. Precautions should be taken when working around an old or abandoned roost site. It is wise to test for the presence of histoplasmosis before beginning any work. Wear a self-contained breathing apparatus or face mask with a dust filter (less than 2 microns) to prevent inhalation of the spores. Wear protective clothing, gloves, and boots that can be removed and disinfected with formalin and washed. If an area that was once a bird roost is going to be cleared or bulldozed, the area should be dampened with water or work should be done when the weather is wet or cold or both. Avoid working under dry, dusty conditions in late summer. A roost may be decontaminated by spraying it with a 3% to 5% solution of formaldehyde before clearing, but this option is very expensive.
Ornithosis (Psittacosis)
Ornithosis is an infectious respiratory disease caused by Chlamydia psittaci, a viruslike organism that affects humans, pets, and livestock. It usually leads to a mild pneumonia-or flu-like infection, but it can be a rapidly fatal disease (less than 1% of the cases reported in the
United States). In humans many cases occur that are undetected or incorrectly diagnosed.
Pigeons are most commonly associated with the transmission of ornithosis to humans. Birds have adapted to the disease and show no symptoms, but act as healthy carriers, shedding the organism in their feces, which later may become airborne as dust. The disease may also be contracted from parakeets, farm poultry, or waterfowl.
People working in dry, dusty areas where bird droppings are present, should wear face
masks or respirators to avoid inhaling airborne avian fecal material. Spray work areas with water and/or disinfectants to minimize the potential for airborne infections particles. Medical attention,including antibiotic treatments are recommended for disease treatment.
Salmonellosis
The Salmonella group of bacteria can also be transmitted by birds. Refer to Commensal Rodent-borne Diseases (above) for additional information.
Other Bird-borne Diseases
Pigeons, starlings, sparrows, blackbirds, and other types of birds have been implicated in the transmission of various diseases of significance to humans or livestock. Starlings have been shown to be vectors of transmissible gastroenteritis (TGE) of swine. The virus can be carried in an infective state in the birds’ intestines or on their feet for up to 30 hours. It is generally fatal to baby pigs and causes weight loss in adults. Starlings may also be involved in the transmission of
hog cholera. Cryptococcosis is a fungal disease spread by pigeons and starlings that result in chronic, usually fatal, meningitis. Various species of birds may also play a part in the
transmission of encephalitis, Newcastle disease, aspergillosis, toxoplasmosis,
pseudotuberculosis, avian tuberculosis, and coccidiosis.
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