Chlamydophila psittaci – IgM, IgG and total antibodies; Molecular diagnosis (PCR and sequencing)
The family Chlamydiaceae includes two genera Chlamydia and Chlamydophila. The species of these genera, pathogenic for animals and man, and of clinical importance are: Chlamydia trachomatis, Chlamydophila pneumoniae and Chlamydophila psittaci.
Chlamydophila psittaci, is a strict intracellular bacterium known throughout the world for causing avian chlamydiosis. This disease was initially called psittacosis, but later the term ornithosis was introduced to differentiate the disease in domestic birds from that of psittacine birds. Outbreaks of avian chlamydiosis in psittacines and poultry farms cause considerable economic losses.
The infection of birds by Chlamydophila psittaci, can lead to a systemic and sometimes fatal disease, common throughout the world that has been found in more than 500 species of birds belonging to more than 30 genera. Clinical signs are generally nonspecific and highly variable in severity and depend on the species and age of the bird, as well as on the infecting strain. The primary reservoir is birds, particularly parrots and parakeets, but several recent studies suggest a significant prevalence of Chlamydophila psittaci in chickens from the food industries and wild pigeons.
Avian chlamydiosis can produce lethargy, hyperthermia, abnormal secretions, rhinorrhea and tearing, and a decrease in egg laying. Mortality is very variable. In domestic birds, the most frequent clinical signs are conjunctivitis, anorexia and weight loss, diarrhea, yellowish deposits, sinusitis, biliverdinuria, rhinorrhea, sneezing, tearing and respiratory distress. In many birds, especially in the elderly psittacidae, it can present without clinical signs, although, nevertheless, they eliminate the agent for long periods of time. Necropsy of affected birds is frequently observed splenomegaly and hepatomegaly, fibrinous inflammation of the air sacs, pericarditis and peritonitis. The histological lesions point to the presence of the infection, but they are not pathognomonic unless they are accompanied by the identification of chlamydia.
The transmission between birds is mainly through the inhalation of aerosols containing dried infectious particles from the faeces of contaminated birds. Transmission to humans is closely related to contact, sporadic or permanent, with companion birds such as parrots, or domestic birds present in zoos or farms, so it should not be considered only a professional zoonosis, although the risk of psittacosis is more elevated in individuals in direct contact with birds. Transmission in humans is also related to the inhalation of contaminated aerosols, generated from the excretions of the avian respiratory tract and excrement, and may cause a mainly respiratory disease, which can lead to severe atypical pneumonia with death in the most severe cases.
Interhuman transmission is possible, but it is considered rare. Human psittacosis tends to affect young males more, although this fact may be biased for occupational reasons of exposure. Before the introduction of antibiotics, mortality in humans due to psittacosis was 10 to 20% but decreased to 1% since the use of antibiotics.
Since the beginning of the twentieth century there have been pandemic outbreaks, which have been linked on numerous occasions with the importation of psittacine birds from South America to Europe or North America. The measures of isolation of imported birds and the treatment with tetracyclines drastically reduced the cases of human psittacosis (~50 cases/year). However, in recent years several cases of human infections associated with outbreaks of avian chlamydiosis have been reported in several European countries, especially in turkey and duck farms.
The clinical manifestation of human psittacosis varies from a flu-like illness to severe atypical pneumonia. Recent studies demonstrated the ability of Chlamydophila psittaci to infect bovines with the same tissue tropism as in humans, the respiratory tract and the same result, the respiratory tract infection.
Genotyping of Chlamydophila psittaci
Until recently, nine different genotypes have been clearly differentiated according to the ompA gene that encodes the main outer membrane protein (MOMP). Seven of these "classic serovarieties" are considered to occur mainly in a specific order or class of birds and two in non-avian hosts:
1. Genotype A in psittacine birds.
2. Genotype B in pigeons.
3. Genotype C in ducks and geese.
4. Genotype D in turkeys.
5. Genotype E in pigeons, ducks and other birds.
6. Genotype E / B in ducks, turkeys and pigeons.
7. Genotype F in parakeets.
8. Genotype WC in cattle.
9. Genotype M56 in rodents.
Most avian genotypes have also been identified sporadically in strains of cases of zoonotic transmission to humans, especially A, B and E / B. Meanwhile, subgroups have been introduced for three of the most heterogeneous genotypes, which would correspond to the following: A-VS1, A-6BC, A-8455, EB-E30, EB-859, EB-KKCP, D-NJ1 and D -9N In addition, six new provisional genotypes have been suggested to include strains that were previously not typable: 1V, 6N, Mat116, R54, YP84, and CPX0308, in such a way that the total number of genotypes would amount to 15.
Currently, antibiotics are the only means of control. Chlamydophila psittaci is sensitive to several antibiotics, which must penetrate inside the cells since it is inside where it develops the cell cycle of this bacterium. Of these, the most commonly used are chlorotetracycline, doxycycline and other tetracyclines. The treatment requires staying for a long period of time.
Diagnosis of Chlamydophila psittaci
Serological methods are the basis of the diagnosis of psittacosis. EIA techniques are less sensitive than complement fixation (CF) and indirect micro-immunofluorescence (MIF). MIF or indirect immunofluorescence (IFI) are probably the most sensitive and specific methods. However, it can cross-react with other Chlamydia species.
During the last years, the molecular PCR test has become the method of choice in diagnostic laboratories because it is a technique with high specificity and sensitivity and has the advantages of being simple, fast, easy to standardize and more appropriate, and safe than the culture.
Current PCR tests for the detection of Chlamydophila psittaci target the ompA gene or the intergenic regions of 16S-23S rDNA. Real-time PCR methods that amplify the ompA or envB genes have also been described, using specific probes or SYBR-green staining with different types of samples. These techniques allow detection of infections quickly, starting on the third day of symptoms, which is an advantage over serology. However, they are not commercially available, which requires optimization and prior validation in each laboratory.
The bacterium can be detected in both environmental DNA samples and/or surfaces as well as from cloacal swabs, including embryonic tissues, feces, nasal secretions, fluids, the blood of infected birds, as well as blood, sputum or biopsies of infected human tissues.
Tests carried out in IVAMI:
- Molecular diagnosis (PCR).
- Molecular identification of the species of Chlamydophila psittaci (PCR and sequencing).
- Respiratory samples from both birds, infected humans, feces or blood.
- Environmental and / or surface samples.
Conservation and shipment of the sample:
- Refrigerated: less than 48 hours.
Delivery of results:
- Molecular diagnosis: 24 to 48 hours
- Molecular identification of the Chlamydophila psittaci species: 48 to 72 hours.
Cost of the test:
- Molecular detection of Chlamydophila DNA (PCR): Consult to firstname.lastname@example.org.
- Sequencing of the coding region of the 16S-23S rDNA gene: Consult to email@example.com.