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Lyme Disease Of Pet Birds

Infectious Diseases: Lyme Disease Of Pet Birds

Lyme disease is a tick-borne, multi-system disorder of human and animals and it is characterized by swelling of joints, pain, lameness, fever, lethargy, anorexia, nephropathy with renal failure, myocarditis, cardiac arrest and CNS involvement.
The etiological agent is maintained in tick and several birds and animals. Clinical description of Lyme disease was first documented by Arvid Afzelius, a Swedish dermatologist. The disease was first identified in 1975 (or 1976), among the people suffering with suspected juvenile rheumatoid arthritis in the area of Lyme, Connecticut,  United States. Hence it is known as ‘Lyme disease’ or ‘Lyme Borreliosis’. The causative agent, Borrelia burgdorferi sensu lato (s.l.) was identified in 1982.

Etiology:

Borrelia spirochete is a gram negative, spiral organism with linear chromosome.
The life cycle of Borrelia requires arthropod vectors and mammalian hosts. It belongs to the family Spirochetaceae under the order Spirochaetales. Borrelia spirochetes comprise three distinct species groups i.e. Lyme borreliosis group.

Host Susceptibility:

Borrelia burgdorferi is maintained in nature through a cycle. In the cycle, hard ticks (Ixodes spp, Haemaphysalis spp.) and small mammals (birds, rodents) act as vector and reservoir host, respectively (Table 2.2). The serum complement of the reservoir hosts determines host preference of B. burgdorferi. The bird associated genospecies are resistant to the bird complement but susceptible to the rodent complement.
 Ixodes scapularis and I. pacificus in USA and Canada, I. ricinus in Europe and I. persulcatus in Asia (Japan) act as major vectors of Borrelia burgdorferi s.l. Occasionally, other species of ticks such as I. uriae, I. affinis, I. dammini, I. frontalis, I. angustus Neumann, I. spinipalpis Hadwen and Nuttall, I. auritulus Neumann, I. pacificus Cooley and Kohls are also associated. All of these ticks cannot parasitize human to transmit the spirochete, but, they can act as maintenance host (e.g. I. affinis, I. dentatus). Ixodes persulcatus in Japan and I. scapularis in USA was detected to act as vector of Borrelia miyamotoi.
 Different stages of Ixodes ticks (larva, nymph and adult) can attach with three different hosts to take the blood meal and after engorgement they drop off the host in the environment. Immatured ticks (larva or nymph) prefer to stay in moist areas such as vegetative mat of the forest floor or meadow. Ground-feeding birds (passerines, game birds, sea birds), rodents, lizards act as preferred hosts of the imamatured ticks (Table 2.3). Although, in comparison to rodents, tick infestation in migratory passerine birds is 20–30 times less, but the birds can transmit the infection for long distances. Sometimes, reservoir birds generate mutant and more virulent strains of Borrelia. Passerine birds in mixed coniferous (evergreen) forest were more infected with B. burgdorferi s.l. than the birds in alder swamp forest. Experimentally, Mallard ducks (Anas platyrhynchos platyrhynchos) are susceptible to B. burgdorferi infection and the ducks shed the organism in the droppings. They may transmit the infection without the help of tick vectors. The study indicated that psittacine birds such as yellow naped amazon parrots (Amazona auropalliata) are generally not infected with B. burgdorferi s.l. More studies are needed to explore their resistance status against Borrelia infection. The ticks normally attach with eyelid, head, neck and ventral feather of passerine birds during blood meal (Fig. 2.8). The immature ticks take a blood meal for 2–4 days from their preferred hosts. In adult stage, the ticks attach with the tip of the grasses to get adhere with a large mammalian host. The adult ticks take a blood meal for 5–6 days. The ticks itself have less mobility but they can be carried by their hosts specially the migratory passerine birds across the countries. The seabird tick (I. uriae) is observed to disseminate Borrelia burgdorferi s.l. from one hemisphere to another (trans-hemispheric transmission). In Canada, passerine birds move northward during spring for breeding and nesting and they disseminate ticks with the pathogens. B. burgdorferi is transmitted to immatured ticks from infected birds, rodents and lizards along with the blood meal. The spirochete after transmission multiplies in the gut of the ticks. When the immature ticks molt into adult stage, the numbers of Borrelia spirochete is decreased. During attachment of adult tick with large mammalian hosts, the multiplication of spirochete restarts and the number is increased. The expression of B. burgdorferi outer surface protein (osp) is also changed from ospA to ospC. The ospC helps in transmission of Borrelia from the mid gut to the salivary glands of ticks. Thus, B. burgdorferi is transmitted transstadially from larva to nymph and from nymph to adult. Rarely, within the tick population, B. burgdorferi is transmitted transovarially. When the adult ticks bite a new host, the spirochetes are transmitted from the salivary glands. Possibility of B. burgdorferi transmission by the adult ticks is more than the nymph and larvae, because the adult ticks have two blood meals in different hosts. Sometimes, a single species of tick is infected with more than one numbers of Borrelia genospecies (e.g. B. garinii and B. valaisiana) due to superinfection of the already infected ticks during their consecutive blood meals. Occasionally, two different species of ticks (I. scapularis and I. affinis) may attach with the same Borrelia burgdorferi infected host.

Transmission:

Migratory birds help in spreading Borrelia infected ticks in distant places, from which the infection can be further transmitted to human or other mammals. The migratory birds can act as carrier of previously infected tick or transovarially infected larvae. Occasionally, transmission of Borrelia occurs from the infected ticks to uninfected ticks during their co-feeding from the same birds. The migratory birds not only import the infected ticks in a locality, but also, there is a possibility that local ticks get the infection during attachment with the birds. After a long journey, the birds prefer to take rest in some places for a few days. Recently, role of cottontail rabbit in this transmission cycle is also explored.

Clinical Symptoms:

During carriage of B. burgdorferi most of the birds do not show any clinical symptom or lesion. Experimental inoculation of B. burgdorferi in Canary finches (Serinus canaria) produced only a brief episode of diarrhoea. Natural infestation of B burgdorferi infected tick (Ixodes auritulus) results gasping, lameness and death in fledgling American robin (Turdus migratorius).

Diagnosis:

Clinical Specimens:

For collection of suspected ticks from the migratory birds, the birds are caught by mist nets and are observed carefully for the presence of ticks in head, neck, and beak by magnifying glasses. The ticks are collected by a blunt forcep and are placed in 70% ethanol. They should be labelled properly indicating species of bird and tick, and date of collection. For identification of bird and ticks up to the species level, expertise is needed. From the birds, suspected for B. burgdorferi infection, heparinized blood and tissues from liver, spleen, kidneys can be collected after post mortem.

Diagnostic Techniques:

(a) Direct Examination:

Dark field Microscopy or Giemsa stain can directly demonstrate the Borrelia spirochete in the blood film, liver/spleen smears. FAT can be used for direct examination of the smears.

(b) Isolation of bacteria from clinical samples:

Isolation of Borrelia is difficult due to its slow and fastidious growth and microaerophilic requirements. Modified BSK (Barbour-Stoenner-Kelly) medium is used for isolation of B. burgdorferi s.l. It is an enriched serum broth containing the antibiotics like kanamycin and 5-flurouracil. The media after inoculation is incubated at 33– 34 °C for 3 weeks. The collected heparinized blood sample (0.02 ml) or triturated tissue sample (0.1 ml) can be added in BSK medium (7–8 ml).

(c) Serological tests:

ELISA based kits for detection of total immunoglobulin, Ig G, Ig M against B. burgdorferi s.l is available for human. However, studies in animals (dogs), indicated that results of serological tests are inconclusive. The antibodies may be produced due to earlier exposure specially in those areas where infected tick bite is a common phenomenon. Such kind of serological studies are not conducted in birds probably due to this uncertainty.

(d) Molecular biology:

The whole blood samples collected from the birds can be used for DNA extraction. Whereas, from the ticks, DNA is extracted by spin column technique. PCR for consensus flaB gene of Borrelia and the spacer region between the 5S and 23S rRNA genes can be carried out to confirm Borrelia burgdorferi s.l.

Zoonosis:

Zoonotic transmission of Borrelia burgdorferi s.l. occurs from the bites of infected ticks. The persons during outdoor recreation, professionals such as wildlife and forest caretakers are at high risk. Migratory birds passively maintain the infection in nature. No direct transmission of Borrelia burgdorferi s.l. from the birds to human is evidenced. The infection in human initiates with a red coloured allergic pimple (erythema migrans), and it is followed by fever, headache, fatigue, muscle and joint pain. In severe cases, meningitis, unilateral facial nerve palsy and renal failure occur.

Control Strategy:

Products that kill or repel ticks (e.g. permethrin) can be used in the habitat to reduce the tick density. However, these acaricides may cause environmental hazard and they are only recommended during epidemic situation.

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