Novel aspects of Chlamydophila psittaci pathogenesis in turkeys
A. Lublin*, S. Mechani
Division of Avian & Fish Diseases, Kimron Veterinary Institute
POB 12 Bet Dagan 50250, Israel
*lublina@int.gov.il
H. Yuval
Private poultry practitioner, Herzelia, Israel
Several novel characteristics of Chlamydophila psittaci, formerly named Chlamydia
psittaci, have been found in the recent years in turkeys in a survey that have been
conducted in our laboratory. These findings have not been reported by other
researchers in other places.
Leg arthritis caused by Chlamydophila psittaci. Arthritis caused by Chlamydophila
psittaci was found in a survey on Chlamydophila psittaci in turkeys that was carried
in the last few years in Israel (by using immunofluorescence technique with
fluorescein-labeled monoclonal antibodies against chlamydial LPS, Chlamydia-Cel
Vet IF Test, Cellabs Diagnostics, Australia). Confirmation of immunofluorescence
was conducted in most of the cases by yolk sac inoculation of 6-8-days-old specific
pathogen free embryonated chicken eggs. Infected birds had respiratory system
infections with involvement of pericardium, lungs and air sacs, but also involvement
of joints, therefore lameness is observed as well. In a survey of 52 turkey flocks with
leg problems (including condemnations in slaughter houses), the agent was detected
in joint fluid samples of 44 flocks (85%). In 31% of affected flocks the infection was
limited to joints and in the rest it was systemic and included also internal organs. Joint
isolates were more virulent than the others when test-inoculated into chicken embryos
(47% embryonic mortality vs. 21% from organs other than joints). The predominant
joints with Chlamydophila infection are hock joints but also tarsal joints may be
found infected. In many of the cases the only cause of infection was Chlamydophila
psittaci, but in some of them it was mixed with other common causes of arthritis like
Mycoplasma (Mycoplasma synoviae) and staphylococci (Staphylococcus aureus), the
latter as secondary infection. It may be speculated that the locomotive system is
involved in some of Chlamydophila psittaci infections in turkeys.
Vertical transmission of Chlamydophila psittaci. Finding Chlamydophila psittaci in
turkey embryos and 1-day-old poults in our laboratory suggested that egg
transmission of Chlamydophila psittaci may take place in turkeys, as was reported in
1972 by Wilt et al. in snow geese and few other species (ducks, sea gulls and
parakeets), and in 1993 by Wittenbrick et al. as sporadic cases in chickens.
In turkey breeders surveyed for vertical transmission of Chlamydophila psittaci from
mother to chick, high prevalence of the pathogen was demonstrated in genital organs
of laying females (ovaries, oviducts) and in male genital system (testes) including
semen, as in embryos and 1-day-old chicks. Almost all the examined breeding flocks
were also sero-positive to the agent.
Scores of immunofluorescence test in infected 1-day-old chicks were higher than
those of the embryos before hatching, probably due to the stress of hatching process.
Passive maternal antibodies of Chlamydophila psittaci passing from mother to chick
have been detected in blood and yolk sacs of chicks but declined in blood by the age
of 3 weeks.
In young chicks (up to 5-day-old) the agent have been detected usually in the extraembryonic membranes (mostly the chorioallantoic membrane but in elder embryos
also in yolk sac). In embryos elder than 2 weeks the agent was found also in internal
organs (heart, lungs, liver, spleen). In comparison to infected adult birds with
histopathological changes in various tissues, infected embryos were histologically
normal, probably because most of the changes happen in chronic and not in acute
cases.
Ischemia in head region probably caused by Chlamydophila psittaci. Ischemia in the
head region of meat-type turkeys have been occurred in Israel since 1995. The
syndrome is characterized by necrotic areas, initially in the head skin and wattles and
later in the thoracic region and on toe skin in a few cases, with a color changing from
reddish to blue or black, together with atrophic changes of pectoral muscles. Clinical
signs include severe depression, anorexia, apathy, leg weakness and diminishing of
movement ability, mild to severe cyanosis, signs of shock, and in some of the cases
dyspnea and respiratory disturbances. Morbidity rate may reach 20-40% within 3-5
days, and mortality rate may stay low or increase gradually from less than 0.5% per
day to 1.5% per day.
Within a few days the infected birds develop the necrotic areas on the wattles and
head skin. Post mortem examination reveal lesions such as white streaks in the
superficial pectoral muscles and necrotic regions in the internal pectoral muscles, pale
swollen kidneys and a small-sized spleen in most birds but splenomegaly in a few of
them. Blood smears reveal acute heterophilia within a few days after the appearance
of clinical signs in the flock, and an increase in young white blood cells. Clinical
signs usually last for at least 10 days.
The disease could usually be cured within 24-48 hrs after oxytetracycline treatment.
However, in some of the cases its curative efficacy as was observed, diminished with
every new presentation of the syndrome.
None of the “ordinary” viral, bacterial or fungal pathogens were isolated from these
birds, and all PCR tests of various viral agents including lymphoproliferative agents
were also negative.
The syndrome could be reproduced by parenteral administration of tissue
homogenates (liver, spleen, kidneys and brain) from affected turkeys or whole blood
with EDTA from these, taken at early stage of the syndrome, into 8-10-wk-old naive
turkeys. High numbers of Chlamydophila psittaci inclusions were observed in the
tissue homogenates and in the blood. Blood samples taken 2 wks post inoculation,
most of them from birds with signs of ischemia, were sero-positive to Chlamydophila
psittaci antibodies (Immunocomb ELISA kit, biogal Galed Labs., Israel) in
comparison to sero-negative blood samples taken prior to the inoculation.
Some of the affected skin regions in the early stage of the syndrome (before the skin
dried) were full of Chlamydophila psittaci inclusions inside erythrocytes as tested by
immunofluorescence. The agent had been isolated in embryos after administration of
organ homogenates from affected turkeys.
In contrast to inoculated turkeys, no clinical signs or any pathological changes could
be observed in mice after inoculation with the same tissue homogenate or with bloodEDTA from affected turkeys that could reproduce the ischemic syndrome in turkeys.
The described phenomenon of necrotic regions in non-feathered skin areas has not
been recognized and no reports of it have yet been published anywhere other than in
Israel. According to the clinical and pathological progress of the disease in the
described cases, and especially the skin lesions, two kinds of bacterial candidates have
been considered, Rickettsiae and Chlamydophila psittaci, both of which are obligate
intracellular parasites. The cutaneous lesions are typical to both pathogens that infect
mainly endothelial cells of small blood vessels and sometimes epithelial cells
(especially Chlamydophila), causing hyperplasia and localized formation of thrombi
that leads to obstruction of blood flow (ischemia) and accumulation of inflammatory
cells near the affected blood vessels, probably with involvement of endotoxins.
Additional arguments in favor of Chlamydophila include the positive sero-conversion
in the disease-reproducible turkeys and identification of Chlamydophila inclusions in
the infective materials as in the blood and organs of the affected birds. Also, we could
not reproduce any clinico-pathological effects in mice, similarly to our previous
findings in concerning Chlamydophila isolates from turkeys. All these additional
arguments cannot be claimed for Rickettsiae.
To summarize, a toxic effect probably caused by Chlamydophila psittaci may be
responsible for the superficial cutaneous effects that have been observed together with
respiratory distress in several meat-type turkey farms in Israel in the last decade.
These signs have not hitherto been associated with Chlamydophila psittaci and the
mechanism of the apparent pathogenesis still remains to be elucidated.
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