Analysis of seroprevalence against Coxiella burnetii in a sample of farm workers in Western Sicily
Verso MG¹, Vesco G², Villari S², Galluzzo P², Gargano V², Matranga D³, De Marchis P¹, Picciotto D¹
¹ Department of Sciences for Health Promotion and Mother-Child Care “G. D’Alessandro”, Occupational Health Section, University of Palermo, Italy
² Istituto Zooprofilattico Sperimentale della Sicilia, Via Gino Marinuzzi, 3, 90129 Palermo, Italy.
³ Department of Sciences for Health Promotion and Mother-Child Care “G. D’Alessandro”, Hygiene Section, University of Palermo, Italy
INTRODUCTION AND OBJECTIVE:
Little is known about the development of chronic Q fever caused by Coxiella burnetii in occupational risk groups and in the general population in Italy, as well as in many countries in the world. The aim of this study was to highlight the presence of the infection in a sample of workers operating outdoors (but not directly in contact with animals), in three provinces of western Sicily, in order to detect the human seroprevalence and compare the obtained data with those found in animals raised in the same territory.
MATERIALS AND METHODS:
The study included 126 generic seasonal agricultural workers (labourers), 84 male and 42 female; none of whom were aware of any previous contact with Coxiella burnetii. Their immunologic status against Coxiella burnetii was tested through research and titration of both phases I and II specific antibodies (IgG) with an indirect immunofluorescence assay, using anti-antibodies labeled with fluorescein isothiocyanate. All data were statistically analyzed, comparing all positive results from the three provinces through variance analysis, and then comparing human results with those obtained from animals raised in the considered areas, specifically, 1,511 cows, 46 of which were found positive (3.04%), and 3,391 sheep, 548 of which were found positive (16.16%).
Anti-Coxiella antibodies were found in nine of 42 females sampled (21.4%; 95%CI=[9.0-33.8]) and 21 of 84 males sampled (25.0%; 95%CI=[15.7-34.3]). 60% (18 of 30; 95%CI=[42.5-77.5]) of seropositive samples were positive either for Phase I antigen or for both Phase I and II antigens, representing cases of chronic infection. Applying Spearman’s rank correlation, the percentage of seropositive humans was significantly correlated with that observed for sheep (r=1.00; p<0.001), but not for cows (r=-0.5; p=0.667).
The results obtained, although based on a small sample, suggest that the disease is present in the territory of Western Sicily, both in animals and in humans. A closer collaboration between doctors and veterinarians is therefore necessary to fight against the spread of the infection.
- PMID: 27007520; DOI:10.5604/12321966.1196855
Q fever is an infectious disease caused by Coxiella burnetii, an obligate intracellular pathogen infecting different animals, especially cows, sheep and goats, usually through ticks that act as carriers. Sometimes also humans can be infected through inhalation of dust coming from infected stables, slaughterhouses, or animal derivatives (skins, wool), and they show symptoms similar to the influenza and in severe cases also pneumonia.
The disease, present throughout the world, is an occupational hazard for those who work in rural settings and in contact with animals, especially the operators of livestock industry (farmers, veterinarians, tanners, and wool carders).
Diagnosis is based on clinical signs and a specific serodiagnosis, using methods such as indirect immunofluorescence (IFA), ELISA and complement fixation test (CFT) for the detection of phase I (corresponding to the chronic form) and phase II antibodies (corresponding to the acute form of the disease), specific against the two different antigenic phases of C. burnetii. Molecular diagnosis through the research of bacterial DNA is increasingly being used.
Q fever is very often asymptomatic, so that the available data often underestimate the size of the phenomenon in a lot of Countries, both in general population and in workers. At the present time, in Italy and in other European countries the exact number of humans and ruminants with Q fever infection is unknown, often because people with antibodies against Coxiella burnetii show no obvious signs of the disease.
Through our study, we wanted to highlight the spreading of the infection with Coxiella burnetii in a sample of outdoors workers (not directly in contact with animals), in three provinces of western Sicily (Palermo, Trapani and Agrigento), in order to detect the human seroprevalence and compare the obtained data with those found in animals raised in the same territory.
The study included 126 generic seasonal agricultural workers (laborers), 84 male and 42 female, without personal history of the disease and without actual symptoms.
We tested their immunologic status against Coxiella burnetii through research and titration of phase I and II specific antibodies (IgG), using anti-antibodies labeled with fluorescein isothiocyanate. The blood sera determining elementary bodies visible and fluorescent when diluted 1:16 were assessed as positive. All data were statistically analyzed.
Anti-Coxiella antibodies were found in nine of 42 females sampled (21.4%) and twenty-one of 84 males sampled (25%). Sixty percent (18 out of 30) of seropositive samples were positive either for Phase I antigen or for both Phase I and II antigens, representing cases of chronic infection.
To study the spread of the infection in cows and sheep raised in the same provinces, we analyzed data collected from surveys carried out by Istituto Zooprofilattico Sperimentale of Sicily in various farms of the three provinces. The percentage of seropositive humans was statistically correlated with that one observed for sheeps, but not for cows.
This study suggests that this disease is present in the territory of Western Sicily, infecting asymptomatic people found seropositive even if not in direct contact with animals, neither clinically diagnosed for Q fever, and it represents a job related risk in outdoors workers.
It’s hard to estimate the true prevalence of the human disease, due to the lack of sufficient similar data for the exposed population in Italy as well as in other Countries, because data are fragmentary and scientific studies are not always updated, oppositely to other zoonosis such as brucellosis, rickettsiosis or leishmaniasis. So exists the tangible risk to underestimate the cases in the population, with missing or incorrect diagnosis in both acute events and chronic infections, along with resulting organ damages. The rarity of current disease reports could also be related to the several infections being completely asymptomatic or accompanied by atypical symptoms, hardly distinguishable from those caused by other diseases.
In this study all subjects showed no signs or symptoms of respiratory disease, and did not report any suggestive episode attributable to the time of infection. We will expand the study in the next future, enrolling subjects with other work tasks not at direct risk of infection, to compare with those farmers, in order to help assessing the related risk with this profession in the Sicilian region, where the disease has been described many decades ago.
It would be desirable and very helpful if there were greater collaborations between doctors and veterinarians, because the strategy to combat the spread of Q fever infection in humans can only be related to a better control of the pathogen in animals.
This work was supported by grant IZS SI 05/12 RC from the Italian Health Ministry.