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Tick Borne Crimean-Congo Haemorrhagic Fever in Fars Province, Southern Iran: Epidemiologic Characteristics and Vector Surveillance



Fakoorziba , M.R. , M. Neghab, H. Alipour and M.D.Moemenbellah-Fard
 
ABSTRACT

Crimean Congo Haemorrhagic Fever (CCHF) is an acute fatal viral infection caused by a virus from Bunyaviridae family, genus Nairovirus. The virus has been isolated from at least 31 species of ticks: among them Hyalomma species are the most important vectors. Geographically, CCHF is a widespread viral infection. Its mortality rate in Iran has been estimated to be 29.6 and 11.9% in 1999 and 2000, respectively. The majority of CCHF cases could be prevented. However, in order to identify and prioritize areas for prevention, to the best of authors` knowledge to date, no systematic study has been carried out in Fars province, Iran, to assess the extent, frequency and major outcomes of this fatal infection. The current descriptive retrospective case series study was, therefore, undertaken to address some of these issues. Data on CCHF cases for a period of four years (2001-4) were collected from different official sources in Iran. Data were categorized and analyzed by SPSS software, version 13/5. Gender, age, occupation, seasonal distribution and outcome of the disease were considered in data analysis. A total of 45 cases had been registered during the study period of which 29 were suspected and 16 were confirmed cases. CCHF was more common in men (85.5%) than in women (14.5%). Similarly, the disease was more prevalent in the 20-29 years old age group (37.5%). Nineteen cases (42%) resulted in death. Seasonal distribution of the infection revealed that it was more common in spring (37.5%). Additionally, 38% of the CCHF cases occurred among butchers, slaughterhouse workers, farmers and shepherds. The case fatality rates for the suspected and confirmed cases were 55.1 and 18.75%, respectively. Data gathered from different areas of Fars province showed that out of the 18 species identified to be the potential vectors of CCHF, 13 exist in this geographical area. In conclusion, the observation that butchers, slaughterhouse workers, farmers and shepherds form the most commonly affected occupations, indicate areas where preventive interventions, in particular health education efforts, might be usefully targeted.

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  How to cite this article:

Fakoorziba , M.R. , M. Neghab, H. Alipour and M.D.Moemenbellah-Fard , 2006. Tick Borne Crimean-Congo Haemorrhagic Fever in Fars Province, Southern Iran: Epidemiologic Characteristics and Vector Surveillance. Pakistan Journal of Biological Sciences, 9: 2681-2684.

DOI: 10.3923/pjbs.2006.2681.2684

URL: https://scialert.net/abstract/?doi=pjbs.2006.2681.2684

INTRODUCTION

Crimean-Congo Haemorrhagic Fever (CCHF), an acute potentially fatal arboviral human disease, is caused by a zoonotic tick-borne virus which is the type species of the Nairovirus genus within the family Bunyaviridae (Hoogstral, 1979). This CCHF arbovirus is an enveloped, single-stranded negative-sense RNA virus with tripartite circular genomic segments (Nuttall, 2001). It infects mammals like rodents, leporids and ungulates and/or birds to different extent. Birds, in particular, play an important role not only as a source of blood but also as phoretic hosts in disseminating ticks. Although hard (Ixodidae, mainly Hyalomma genus) and soft (Argasidae) ticks transmit CCHF virus to a vast variety of animals, the severe pathogenesis only affects humans (Nuttall, 2001). The human disease is, however, sporadic but a cause of concern due to high mortality and transmissibility through contact with patients. Viral control thus requires the highest level of laboratory containment, which is maintained at biosafety level 4 conditions (Karti et al., 2004). CCHF occurs sporadically in regions of Africa, Asia and Eastern Europe (Hoogstral, 1979: Fisher-Hoch et al., 1995). It is characterized by Disseminated Intravascular Coagulation (DIC) with capillary fragility, frequent extensive ecchymoses, severe bleeding and hepatic dysfunction with case fatality rates ranging from 8% to 90% (Altaf et al., 1998; Williams et al., 2000) and an average mortality rate of about 30% (Nuttall, 2001).

CCHF virus is usually transmitted to humans by direct infected tick bites, dermal contact with viremic domestic livestock or its freshly slaughtered tissues, contaminated blood or other body fluids of human and animal, viremic blood transfusion and direct nosocomial exposure to patients. The main objective of this study was to assess the epidemiological characteristics and vector surveillance of CCHF in Fars province and to propose precautionary measures to reduce future disease outbreaks in this region.

MATERIALS AND METHODS

This survey was conducted on CCHF cases for a period of four years (2001-04) in Fars province, southern Iran. It was a retrospective case series study and the data were gathered from the Iranian Pasteur Institute and the center for Communicable Diseases Control (CDC) in Fars. Table 1 shows a set of screening evaluations for CCHF cases involving a series of historical, physical and routine laboratory measures. All suspected, probable and confirmed (definite) cases were covered.

A probable case was defined as an acutely ill person with clinically observed signs and symptoms of sudden onset of fever, headache, myalgia and bleeding: epidemiological risk factors (e.g., history of tick bite, contact with suspected cases of CCHF, contact with domesticated animals and their products and travel to, or residence in, an endemic area for CCHF).

A suspected case was defined as one with above-named features as well as laboratory data including a platelet count of <150000 cells mm3 and a leucocyte (WBC) count of <4000 mm3.

Table 1: Screening evaluations for CCHF cases
*WBC = White Blood Cell; **Hb = Hemoglobin; ***AST = Aspartate aminotransferase; ****ALT = Alanine amino transferase

The case definition for confirmed (definite) persons with CCHF was rescheduled as individuals who met the criteria for a probable case and positive serological test results for Enzyme-linked Immunosorbent Assay (ELISA) of IgM and/or rising titers of IgG antibodies or with a positive test for reverse transcription polymerase chain reaction (RT-PCR).

The epidemiologic data on such variables as age, gender, job, season, nationality, etc. were retrospectively collected for all cases. These were analyzed using SPSS version 13/5 software and statistical inferences were performed.

RESULTS

In general, a total of 45 cases were reportedly registered during the four years study period. Twenty nine patients (64.5%) were suspected and 16 cases (35.5%) were confirmed to be CCHF-positive. Sixteen people (55%) from suspected cases and three patients from confirmed cases passed away, which gave a Case Fatality Rate (CFR) of 18.75% in the latter case (Table 2). Among all these cases, 71% were male and 29% were female. The most frequent suspected cases were among housekeepers (38%) and additionally the highest CFR(12.5%) were found in men.

The highest positively confirmed cases were among abattoir workers and butchers (37.5%) and farmers (31.25%) (Table 3). Moreover, the most frequent IgM positive cases (37.5%) and suspected cases (51.7%) were observed in the spring season, while in the winter, the lowest IgM-positive cases (12.5%) and suspected cases (10.3%) were reported.

Table 2: General statistics for CCHF cases
*CFR: Case Fatality Rate

Table 3: Occupation–related data of CCHF cases.

Table 4: Epidemiological data related to CCHF cases

Table 5: Scientific names of tick vectors of CCHF virus found in Fars province.

The most frequent suspected cases (41.4%) and positively confirmed cases (37.5%) were in the 20-29 years old age group. The confirmed cases of CCHF occurred in the 10-69 years old age group. Additionally, the most frequent suspected cases (62%) and positively confirmed cases (87.5%) were seen in males (Table 4).

From a total of 31 different soft and hard tick species and subspecies recognized to be the vectors of CCHF virus worldwide, 13 species were identified to be prevalent in Fars province that two of these were argasid (soft) ticks (Table 5). The two-host hard ticks, Hyalomma species, were the most prevalent (54%) of all species in this region.

DISCUSSION

CCHF virus is a microparasite of engorging hard and soft ticks. It is a polythetic zoonotic arbovirus with wide spectrum host specificity. The viral agent can be transmitted trans-stadially and transovarially in ticks (Fisher-Hoch et al., 1995). Direct transmission through contact with infected blood and body fluids and possibly crushed ticks is an important route of human infection. The Iranian CCHF viral clade (GenBank Accession No. AY366373-9) (Karti et al., 2004) is clearly distinct from Turkish clade, but shows some phylogenetic affinity with Pakistani clade. This linkage could reinforce the idea that illegal cross-border livestock movements are presumably responsible for sporadic CCHF outbreaks in Iran. Nevertheless, epidemics of CCHF are usually focal and due to the close proximity of people to domesticated livestock and their associated viremic ticks, even in urban areas, the disease has a peridomestic nature (McCormick and Fisher-Hoch, 2000). In fact, raised anti-CCHF viral antibody titers in humans and domesticated livestock emphasize the facility of transmission.

Of the viral haemorrhagic fevers, CCHF has the most florid haemorrhage and highest frequency of large ecchymoses. It is a disease that develops quickly following infection. Viral antigenic variation, mode and dose of inoculation may all be critical in determining the severity of disease. Man is the final accidental dead-end host for CCHF virus, and astonishingly, seems to be the only species in which CCHF virus generates severe disease.

The Case Fatality Rate (CFR) varies from one place to another reflecting to some extent the strain differences in virulence, variable access to medical and diagnostic services, variable exposure level to viremic vectors, mode of transmission, etc. In southern Russia, CFR varies thus from 5 to 10% (McCormick and Fisher-Hoch, 2000). In Turkey, Iran, Mauritania, Bulgaria, Senegal, Iraq, Dubai, and Pakistan: the CFR values were 11.0: 11.6, 19.2, 24.1: 28.6: 21.8: 30.0 and 22%, respectively (Karti et al., 2004; Mardani et al., 2003; Alavi-Naini et al., 2006; Sharifi et al., 2006; Nabeth et al., 2004a; Papa et al., 2004; Nabeth et al., 2004b; Al-Tikriti et al., 1981; Suleiman et al., 1980; Burney et al., 1980). In the present study, The CFR was 18.75% which is consistent with other reports.

The seasonal distribution of CCHF cases to a large extent is dependent on climatic conditions as well as the local tick host populations. In Iran, the disease is common in the spring months of April to June, as found also in this study. Any sex difference in CCHF cases is mainly due to gender disparities in agricultural and farming practices. Sheep handlers appear to be mostly at risk. As abattoir workers, butchers, shepherds and other similar occupations are mostly male-oriented: it is not unexpected to find that, as in this study, males are mainly infected with CCHF viruses.

Some two-or three-host species of hard ticks have developed the ability for each postembryonic stage to feed on a larger-sized wandering mammal. Under natural conditions, it is seldom so if ever absolutely established. Rather, each stage may feed on the larger-sized host but under other conditions immature stages parasitize smaller sized hosts. The potential for this type of host dichotomy, which is more frequent in some species of Hyalomma than in other genera, has numerous epidemiological implications. Innumerable immature stages of the Hyalomma marginatum complex are carried intercontinentally by a large number and variety of northward and south migrating birds (Desch et al., 1984).

ACKNOWLEDGMENTS

The authors wish to thank Mr. Vahid Khatemi Fard research student of college of health for gathering data, the authoritiesat the center for Communicable Diseases Control (CDC) and the Pasteur Institute of Iran, Tehran, for permitting the author use their facilities. This study was in part funded under the auspices of research department of Shiraz University of Medical Sciences by the research project authentication number 84-2453 dated on 15th Aug. 2005.

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