Juvenile, female bronze-winged Parrot (Pionus chalcopterus).Numerous birds of a flock with various parrots died spontaneously or after a short episode of unspecific symptoms.
Necropsy revealed hepatomegaly and multifocal randomly distributed white foci in the liver. Spleen and kidneys were swollen and moderate numbers of adult Ascaridae were present in the duodenum.
Liver: The liver architecture is multifocally disrupted by randomly distributed areas up to 0.1 cm in diameter characterized by loss of cellular detail, karyorrhexis, karyolysis, and deposition of cellular debris (necrosis). Foci are surrounded by moderate numbers of degenerated and viable heterophils and macrophages. Occasionally hepatocytes and Kupffer cells contain intracytoplasmic grey indistinct granular structures. Increased numbers of aforementioned cells are also present within the sinusoids. Multifocally, most often surrounding bile ducts are moderate numbers of mainly lymphocytes, plasma cells, and fewer macrophages. Multifocally, bile ducts are minimal hyperplastic and occasionally ectatic. Additionally, the liver is diffusely congested.
Giemsa staining revealed multifocal dark purple cytoplasmic inclusions in both hepatocytes and macrophages.
Liver: Hepatitis, chronic-active, multifocal, random, necrotizing and granulomatous, moderate to severe, with intracellular bacteria consistent with Chlamydophila psittaci, bronze-winged parrot (Pionus chalcopterus), avian.
PCR tested negative for avian bornavirus. Ziehl-Nielsen staining of a liver imprint failed to identify acid-fast bacteria.
Chlamydia psittaci, parrot
The members of the order Chlamydiales are obligate intracellular, gram-negative bacteria depending on the host cells energy resources (ATP). They have a biphasic life cycle with the infectious form that enters the cell (elementary body, EB), the intracellular, metabolic active, replicating form (reticulate body, RB) and the intermediate body (IB) with morphologic characteristics between EB and RB.
Infection with C. psittaci occurs primarily via inhalation, ingestion or conjunctival exposure to contaminated feather dust or faeces. The bacteria spread to lung, air sacs and pericardial sac within few hours. EBs attach to microvilli of the host cell membrane and are internalized via invagination.(4) Bacteria-containing endocytic vesicles are called inclusions. They proceed to the nuclear area where EBs differentiate into RBs. A role of snapin (a part of the SNARE complex) connecting chlamydial inclusions with the microtubule network by interacting with both IncB and dynein has been proposed.(1) RBs replicate via binary fission and reorganize, through IBs, into new EBs. New EBs are released from host cell via cell lysis or exocytosis. In high pathogenic serotypes the inclusion membrane degrades mainly during the active multiplication, releasing the bacteria into the cytoplasm, leading to cell lysis.(7) The rapid multiplication leads to bacteraemia within 48 hours. Infectious EBs are spread via cloaca and/or nasal turbinates into the environment.
Typical clinical findings include diarrhoea and excretion of green to yellow-green urate. Severely affected birds may become anorectic and produce sparse, dark green droppings, followed by emaciation, dehydration and death.
Typical gross findings are hepatomegaly and splenomegaly with or without necrotic foci, often accompanied by fibrinous airsacculitis, pericarpditis and peritonitis and serous to purulent conjunctival exudate.
The genus Chlamydophila contains six species: C. abortus (ruminants), C. caviae (guinea pigs), C. felis (felidae), C. pecorum (ruminants, swine, koalas), C. pneumonia (humans, marsupialia and amphibia) and C. psittaci (birds). Chlamydophila spp. are known to infect at least 469 domestic, free-living or pet bird species in 30 orders.(3) Of the nine known outer membrane protein A (ompA) subtypes of C. psittaci, seven are known to naturally infect birds (A F and E/B) and two to infect mammals (M56 muskrat and snowshoe hare, WC cattle). Each avian serotype seems to be associated with a different group or order of birds.(2) Furthermore, strains of C. psittaci fall into two general categories: highly or less virulent strains. Highly virulent strains or toxigenic strains (e.g. serotype D) are isolated most often from turkeys and occasionally from clinically inapparent wild birds. In natural and experimental hosts, they are responsible for a rapid and fatal disease progression characterized by extensive vascular congestion and inflammation of vital organs. Veterinarians and poultry workers are especially at risk of becoming infected with serovar D strains. Strains of low virulence (e.g. serotype B and E) cause slowly-progressing epidemics with a mortality rate of less than 5% and neither develop severe vascular damage nor severe clinical signs.(6) They are routinely isolated from pigeons and ducks. Chlamydiosis may be accompanied by concurrent infection with Salmonella spp, especially in pigeons, ducks and some psittacine birds. Avian strains can infect humans and may lead to severe pneumonia. However, cases of human-to-human transmission rarely occur. Immunity to chlamydia is generally poor and short-lived. Older birds are often more susceptible to clinical signs than younger ones.
Liver: Hepatitis, necrotizing, random, multifocal, moderate with diffuse hepatocellular degeneration.
Multifocal and random foci of coagulative and lytic necrosis effacing hepatic parenchyma were the predominant histologic features observed by conference participants. In less affected/non-necrotic parenchyma, changes indicative of hepatocellular degeneration including hepatocyte swelling, pallor, and centrilobular to midzonal vacuolar change were also described. Bile ducts containing blood and inflammatory cells were noted; however, this finding was deemed incidental and, in this case, unrelated to the pathogenesis of C. psittaci. Conference participants rarely identified 1-2um, pale basophilic to amphophilic, intracellular organisms in macrophages and hepatocytes, most consistent with C. psittaci organisms. Slide variation regarding presence of organisms, was noted amongst conference participants. Although not available for this conference, participants discussed various histochemical stains including Macchiovello and Gimenez stains, to identify and/or better highlight organisms in C. psittaci suspect tissues. Common postmortem findings in C. psittaci infected birds include hepatomegaly and splenomegaly, both which were observed grossly in this case. Histologically, the spleen is another primary organ to identify lesions and organisms. This infection is very common in Amazon parrots, which will demonstrate clinical illness. Pigeons and doves are common carriers, but do not become ill; however, they may facilitate zoonosis.
All genotypes / subtypes of C. psittaci can be transmitted to people and cause psittacosis (i.e. parrot fever), a disease originally named when infection was thought to be only transmitted from psittacine birds. Most cases of human psittacosis are related to contact with psittaciformes; however, it is also an occupational hazard for those working in the poultry industry and others in close contact with different avian species.(8) Infection in humans can result in a wide range of disease from asymptomatic infections to mild influenza-like symptoms, to severe disease with pulmonary and extrapulmonary involvement including gastrointestinal, hepatic, cardiac and neurologic signs.
C. psittaci infection in poultry production operations is most commonly associated with turkey or duck farms, but has also been documented in chickens, more commonly broilers. In chickens, both the ompA genotypes B and the more pathogenic D can cause clinical infection consisting of respiratory symptoms. However, as described above for other avian species, respiratory symptoms are generally more severe in genotype D infected chickens and it may also result in anorexia and mortality. Additionally, genotype D shows significantly higher bacterial replication in infected tissues and may demonstrate systemic dissemination. It is found to be excreted in the cloaca and from the pharynx in infected chickens as seen in other avian species.(9)
Atherosclerosis is frequently seen in captive psittacine birds and is considered the most common vascular disease of birds. Interestingly, it has been associated with the presence of C. psittaci antigen in blood vessels indicating infection may be a risk factor for development of atherosclerosis.(5) However, the exact role of C. psittaci infection in the pathogenesis of atherosclerosis, regarding severity and strain, is unclear.
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9. Yin L, Lagae S, Kalmar I, et al. Pathogenicity of low and highly virulent Chlamydia psittaci isolates for specific-pathogen-free chickens. Avian Diseases. 2013;57(2):242-247.