Crimean-Congo Haemorrhagic Fever: Case study analysis of a sporadic outbreak from Chakwal, Pakistan

Geographical epidemiology of Hyalomma anatolicum and Rhipicephalus microplus in Pakistan: A systematic review

The livestock sector contributes almost 11% of Pakistan's GDP and is crucial to 35 million people's livelihoods. Ticks are a major economic threat, as over 80% of livestock, such as bovines, are tick-infested with Hyalomma and Rhipicephalus tick species. Hyalomma anatolicum and Rhipicephalus microplus are the most common tick species collected from livestock, transmitting primarily anaplasmosis, babesiosis, and theileriosis. We aimed to identify the geographical distribution of these two tick species and hot spot areas where the risk of these diseases being transmitted by these ticks is high. Following the PRISMA guideline, two authors conducted an independent review of literature sourced from various databases. We screened 326 research articles published between January 1, 1990, and December 31, 2023, focused on identifying the tick species at the district level. Thirty studies from 75 districts, representing 49.3% of the country's total area, detected at least one tick species through collection from animals. R. microplus was present in 81% (n = 61) and H. anatolicum in 82% (n = 62) of these sampled districts. We employed spatial and conventional statistical methods with Geographic Information Systems (GIS) after mapping the weighted distribution of both ticks (the number of ticks per standard unit of sampling effort). We identified northwestern and northcentral regions of the country as hotspots with the highest tick distribution, which aligned with the documented high prevalence of anaplasmosis, babesiosis, Crimean-Congo hemorrhagic fever (CCHF), and theileriosis in these regions. This underscores the urgent need for robust tick control measures in these districts to safeguard animal health and boost the livestock economy.

Prevalence of crimean Congo hemorrhagic fever in Khyber Pakhtunkhwa, Pakistan

BACKGROUND

CCHFV is well recognized as a major public health threat and its prevalence and epidemiological distribution in Pakistan and specifically in KP province is not well documented.

METHODS

We used a gold-standard PCR-based diagnostic assay for confirmation of CCHFV among suspected patients. A total of 150 patients were enrolled from June 2022 to September 2022 and their blood samples were collected for PCR confirmation.

RESULTS

The overall positivity rate for CCHFV was 26.67 %, with the virus mostly prevalent in the middle-aged group (21-40 years). In the July of 2022, a significant spike in the prevalence of CCHFV was observed in provincial capital Peshawar with the highest burden (31.57 %).

CONCLUSION

Our findings indicate the necessity of strengthening CCHFV monitoring programs and intensifying efforts to identify hotspot regions for effective surveillance and control of CCHFV. The months before the Eid-ul-Adha are crucial in the context of CCHFV control.

Systematic Review on Crimean-Congo Hemorrhagic Fever Enzootic Cycle and Factors Favoring Virus Transmission: Special Focus on France, an Apparently Free-Disease Area in Europe

Crimean-Congo hemorrhagic fever (CCHF) is a viral zoonotic disease resulting in hemorrhagic syndrome in humans. Its causative agent is naturally transmitted by ticks to non-human vertebrate hosts within an enzootic sylvatic cycle. Ticks are considered biological vectors, as well as reservoirs for CCHF virus (CCHFV), as they are able to maintain the virus for several months or even years and to transmit CCHFV to other ticks. Although animals are not symptomatic, some of them can sufficiently replicate the virus, becoming a source of infection for ticks as well as humans through direct contact with contaminated body fluids. The recent emergence of CCHF in Spain indicates that tick-human interaction rates promoting virus transmission are changing and lead to the emergence of CCHF. In other European countries such as France, the presence of one of its main tick vectors and the detection of antibodies targeting CCHFV in animals, at least in Corsica and in the absence of human cases, suggest that CCHFV could be spreading silently. In this review, we study the CCHFV epidemiological cycle as hypothesized in the French local context and select the most likely parameters that may influence virus transmission among tick vectors and non-human vertebrate hosts. For this, a total of 1,035 articles dating from 1957 to 2021 were selected for data extraction. This study made it possible to identify the tick species that seem to be the best candidate vectors of CCHFV in France, but also to highlight the importance of the abundance and composition of local host communities on vectors' infection prevalence. Regarding the presumed transmission cycle involving Hyalomma marginatum, as it might exist in France, at least in Corsica, it is assumed that tick vectors are still weakly infected and the probability of disease emergence in humans remains low. The likelihood of factors that may modify this equilibrium is discussed.

Immunobiology of Crimean-Congo hemorrhagic fever

Human infection with Crimean-Congo hemorrhagic fever virus (CCHFV), a tick-borne pathogen in the family Nairoviridae, can result in a spectrum of outcomes, ranging from asymptomatic infection through mild clinical signs to severe or fatal disease. Studies of CCHFV immunobiology have investigated the relationship between innate and adaptive immune responses with disease severity, attempting to elucidate factors associated with differential outcomes. In this article, we begin by highlighting unanswered questions, then review current efforts to answer them. We discuss in detail current clinical studies and research in laboratory animals on CCHF, including immune targets of infection and adaptive and innate immune responses. We summarize data about the role of the immune response in natural infections of animals and humans and experimental studies in vitro and in vivo and from evaluating immune-based therapies and vaccines, and present recommendations for future research.

Ticks and tick-borne diseases of bovines in a smallholder livestock context: The Pakistani example

Ticks and tick-borne diseases (TTBDs) substantially affect the health and production of ruminants, particularly in resource-poor, small-scale farming systems worldwide. However, to date, there has been no critical appraisal of the current state of knowledge of TTBDs in such farming systems. In this article, we systematically reviewed the situation in Pakistan-as an example of a country that is highly reliant on agriculture to sustain its economy, particularly smallholder livestock farms, which are continually faced with challenges associated with TTBDs. The main aims of this review were to gain improved insights into the current status of TTBDs in small-scale farming systems, and to identify knowledge gaps, through the systematic evaluation of published literature on this topic from Pakistan, and to recommend future research directions. We searched publicly available literature from three databases (i.e. Web of Science, Google Scholar, and PubMed) on bovine TTBDs in Pakistan. Of 11,224 published studies identified, 185 were eligible for inclusion; these studies were published between August 1947 and June 2021. A critical analysis of these 185 studies revealed that the diagnosis of ticks and tick-borne pathogens (TBPs) in Pakistan has been based largely on the use of traditional methods (i.e. 'morpho-taxonomy'). At least 54 species of tick have been recorded, most of which belong to the genera Haemaphysalis, Hyalomma and Rhipicephalus. The prevalence of ticks was higher, particularly in young, exotic and crossbred female cattle, during the summer season. Major TBPs include species of Anaplasma, Babesia and Theileria, with prevalences being higher in cattle than buffaloes. Additionally, pathogens of zoonotic potential, including species of Anaplasma, Borrelia, the Crimean-Congo haemorrhagic fever virus, Coxiella, Ehrlichia and Rickettsia, have been recorded in both tick and bovine populations. Information on risk factors, spatial-temporal distribution, genetic diversity, and control of ticks and TBPs is limited, the vector potential of ticks and the distribution patterns of ticks and TBPs in relation to climate remains largely unexplored. Future research should focus on addressing these knowledge gaps and the key challenges of poverty, food security and disease outbreaks in a small-scale livestock farming context in order to provide sustainable, environment-friendly control measures for TTBDs.

Prevalence and phylogenetic analysis of Crimean-Congo hemorrhagic fever virus in ticks collected from Punjab province of Pakistan

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne zoonotic disease of human that caused by CCHF virus. To study the epidemiological distribution of CCHFV, 2183 tick samples were collected from sheep, goats, cattle and buffalo of different livestock farms of ten districts of Punjab province of Pakistan. Detection of CCHFV was done using enzyme link immunosorbent assay (ELISA) after proper identification of tick samples. The partial S-segment of CCHFV from ELISA positive tick samples was amplified by PCR and sequenced to determine the genotype of CCHFV. Out of2183 collected tick samples, 1913 ticks belonged to 5 species of genus Hyalomma as H. antolicum (48%), H. marginatum (30.2%), H. rufipes (10.82%), H. impressum (5.43%) and H. dromedarii (5.27%). While 270 ticks belonged to 3 species of genus Rhipicephalus as R. microplus (44.8%), R. sanguineus (32.22%) and R. turanicus (24.8%). The overall antigenic prevalence of CCHFV was found to be 12.13% in collected tick samples and 21 tick pools were sequenced for partial S-segment of CCHFV. All of the 21 tick pools were clustered in genotype IV (Asia-1). The highest prevalence of CCHFV was found in district Chakwal (24.13%) followed by Mianwali (23.68%), Rawalpindi (23.07%), Attock (20.0%), Rajanpur (10.52%) and Lahore (8.33%). In positive tick pools, the highest prevalence of CCHFV antigen was found in H. antolicum (39.6%) followed by H. marginatum (30.18%), H. rufipes (13.2%), H. impressum (3.77%), H. dromedarii (1.88%), R. microplus (5.66%) and R. sanguineus (5.66%). The current study confirms the presence of CCHFV in the ticks population of Punjab. The CCHF virus present in Punjab belongs to Asia-1 genotype. It is important to control the tick infestation of the animals present in these areas. So that the transmission cycle of CCHF can be inhibited.

Exploring the prevalence and diversity of bovine ticks in five agro-ecological zones of Pakistan using phenetic and genetic tools

Tick infestation is a leading cause of tick-worry and tick-borne diseases in livestock and associated economic losses in tropical and subtropical regions of the world. The cattle and buffalo populations in Pakistan are exposed to tick infestation throughout the year, but very little is known about the biology, diversity and distribution of tick species across different agro-ecological zones (AEZ) of the country. The present study aimed to investigate the prevalence (number of bovines infested with ticks out of the investigated population) and diversity of hard ticks infesting bovines in 30 villages located in five distinct AEZs (i.e. Arid, Indus delta, Northern irrigated plain, Sandy desert and Southern irrigated plain). We collected a total of 774 ticks (adult and nymphs) from cattle (n = 116) and water buffaloes (n = 88) on small-holder dairy farms (with <10 bovids per establishment) from September to November 2017. The overall tick prevalence was 46.1% (cattle: 47.9%; buffaloes: 44%), which varied significantly from 22.2% in the Indus delta to 70.5% in the Sandy desert. Tick prevalence was slightly higher in female (46.5%) than male animals (45%), and higher in calves (i.e. ≤ 1 year of age) (55%) than in young animals (i.e. up to 3 years of age) (39%) and adults (48%). Five tick species - Hyalomma anatolicum, Hyalomma hussaini, Hyalomma scupense, Rhipicephalus microplus and Rhipicephalus annulatus - were identified morphologically and then genetically. Genetic identification, achieved using the sequences of two mitochondrial (cytochrome c oxidase subunit 1 and 16S) and one nuclear ribosomal (second internal transcribed spacer) regions, was consistent with the morphological findings. Phylogenetic analyses of the DNA sequence data sets showed that the five species of tick identified here were closely related to the same species or closely related species from within and outside of Pakistan. Of five presently recognised taxa within the R. microplus complex, two were identified herein, including the R. microplus clade C and R. annulatus. This investigation provides the first genetic evidence of the occurrence of R. annulatus in Pakistan as well as Hy. hussaini and Hy. scupense in bovines specifically in the provinces of Sindh and Punjab, respectively. The present findings emphasise the importance of combining morphological and molecular approaches to study the diversity of ticks. Further longitudinal studies are required to establish seasonal variations in the prevalence and distribution of bovine ticks in different AEZs of Pakistan.

Seroprevalence of Crimean-Congo haemorrhagic fever among three selected risk human groups in disease-endemic region of Pakistan

The occurrence of Crimean-Congo haemorrhagic fever (CCHF) in humans is linked with animals living in close vicinity, and information on the incidence of CCHF at the human-animal interface is scarce. Therefore, the current study was designed to identify the high-risk groups of individuals linked with animals in the Chakwal district of Pakistan having a history of CCHF cases in humans. In subject matter, coupled with risk factor analysis, we performed a sero-based CCHF surveillance in three selected risk groups of humans including abattoir workers (n = 137), milkmen (n = 169) and animal handlers (n = 147). Sera samples and questionnaire-based data were collected from each of the participants and screened for anti-CCHFV IgG antibodies using enzyme-linked immunosorbent assay. The highest seroprevalence was observed in animal handlers (n = 14, 9.52%, 95% CI: 4.68-13.99) followed by abattoir workers (n = 9, 6.57%, 95% CI: 2.42-10.72) and milkmen (n = 3, 1.78%, 95% CI: 0.24-4.24). The risk of seropositivity was significantly associated with humans linked with tick-infested animals (OR: 11.0, 95% CI: 1.5-83.0, p = .002), old age >40 years (OR: 6.6, 95% CI: 2.7-16.0, p < .0001), illiteracy (OR: 4.3, 95% CI: 1.5-13.0, p = .004) and humans without knowledge about CCHF (OR: 7.6, 95% CI: 1.8-33.0, p = .0009). The findings of the current study highlighted the seroprevalence of CCHF in high-risk groups of humans living in a disease-endemic area of Pakistan and highlight the need for well-integrated disease surveillance in the future to better comprehend disease control interventions.