Tick-borne encephalitis transmitted by unpasteurised cow milk in western Hungary, September to October 2011

In October 2011, a cluster of four tick-borne encephalitis (TBE) cases was identified in Hungary. Initial investigations revealed a possible link with consumption of unpasteurised cow milk sold by a farmer without authorisation. We performed a cohort study including all regular customers of the farmer. Overall, eleven cases (seven confirmed and four suspected) were identified. Customers who had consumed the farmer’s unpasteurised cow milk had more than a two-fold increased risk for being a TBE case, although not at statistically significant level.

Differential salivary gland transcript expression profile in Ixodes scapularis nymphs upon feeding or flavivirus infection

Ixodid ticks are vectors of human diseases such as Lyme disease, babesiosis, anaplasmosis, and tick-borne encephalitis. These diseases cause significant morbidity and mortality worldwide and are transmitted to humans during tick feeding. The tick-host-pathogen interface is a complex environment where host responses are modulated by the molecules in tick saliva to enable the acquisition of a blood meal. Disruption of host responses at the site of the tick bite may also provide an advantage for pathogens to survive and replicate. Thus, the molecules in tick saliva not only aid the tick in securing a nutrient-rich blood meal, but can also enhance the transmission and acquisition of pathogens. To investigate the effect of feeding and flavivirus infection on the salivary gland transcript expression profile in ticks, a first-generation microarray was developed using ESTs from a cDNA library derived from Ixodes scapularis salivary glands. When the salivary gland transcript profile in ticks feeding over the course of 3 days was compared to that in unfed ticks, a dramatic increase in transcripts related to metabolism was observed. Specifically, 578 transcripts were up-regulated compared to 151 down-regulated transcripts in response to feeding. When specific time points post attachment were analyzed, a temporal pattern of gene expression was observed. When Langat virus-infected ticks were compared to mock-infected ticks, transcript expression changes were observed at all 3 days of feeding. Differentially regulated transcripts include putative secreted proteins, lipocalins, Kunitz domain-containing proteins, anti-microbial peptides, and transcripts of unknown function. These studies identify salivary gland transcripts that are differentially regulated during feeding or in the context of flavivirus infection in Ixodes scapularis nymphs, a medically important disease vector. Further analysis of these transcripts may identify salivary factors that affect the transmission or replication of tick-borne flaviviruses.

Transmission of tick-borne pathogens between co-feeding ticks: Milan Labuda's enduring paradigm

During the 1990s, Milan Labuda's experimental results established a new paradigm for the study of tick-borne viruses that has since been strengthened by its demonstrated effectiveness in explaining the epidemiology of tick-borne encephalitis (TBE). This brief review summarizes the essential features of the transmission of tick-borne pathogens such as TBE virus. Leukocytes migrate between tick feeding sites, bearing infective virions and providing a transport route for the virus between co-feeding ticks independent of a systemic viraemia. Such tick-borne pathogens are thus transmitted from tick to tick via vertebrates; the ticks are the reservoirs as well as the vectors, while the vertebrate is the transient bridge. The aim is to bring the related but non-synonymous terms (co-feeding and non-systemic) to the attention of workers who use simple PCR screening to identify additional vertebrate reservoir hosts of vector-borne pathogens that are not in fact maintained in nature through systemic transmission.

[Prevention of tick-borne meningoencephalitis--summary report]

Tick-borne meningoencephalitis is a zoonosis that shows an upward trend. The causative agent is an RNA virus of the family Flaviviridae whose vector in Central Europe is the castor bean tick (Ixodes ricinus). The infection is most often transmitted via tick bite or, less commonly, by the alimentary route, through the consumption of unpasteurized milk of infected animals. Preventive measures consist in personal protection from ticks, exceptionally in blanket treatment with contact insecticides, in preventing consumption of unpasteurized milk and dairy products from areas with a high incidence of tick-borne encephalitis, and particularly in vaccination of the susceptible population.

Microclimate and the zoonotic cycle of tick-borne encephalitis virus in Switzerland

The focal distribution of tick-borne encephalitis virus (TBEV; Flaviviridae, Flavivirus) appears to depend mainly on cofeeding transmission between infected Ixodes ricinus L. nymphs and uninfected larvae. To better understand the role of cofeeding ticks in the transmission of TBEV, we investigated tick infestation of rodents and the influence of microclimate on the seasonality of questing I. ricinus ticks. A 3-yr study was carried out at four sites, including two confirmed TBEV foci. Free-living ticks and rodents were collected monthly, and microclimatic data were recorded. A decrease in questing nymph density was observed in 2007, associated with low relative humidity and high temperatures in spring. One site, Thun, did not show this decrease, probably because of microclimatic conditions in spring that favored the questing nymph population. During the same year, the proportion of rodents carrying cofeeding ticks was lower at sites where the questing nymph density decreased, although the proportion of infested hosts was similar among years. TBEV was detected in 0.1% of questing ticks, and in 8.6 and 50.0% of larval ticks feeding on two rodents. TBEV was detected at all but one site, where the proportion of hosts with cofeeding ticks was the lowest. The proportion of hosts with cofeeding ticks seemed to be one of the factors that distinguished a TBEV focus from a non-TBEV focus. The enzootic cycle of TBEV might be disrupted when dry and hot springs occur during consecutive years.

[The infection of ixodid ticks collected from humans with the tick-borne encephalitis virus in Tomsk city and its suburbs]

The ticks Ixodes persulcatus and I. pavlovskyi collected from people visited gardens and suburban forests have been examined by the IFA methods on the presence of tick-borne encephalitis virus (TEV). It was established, that the most part of ticks collected from humans belongs to I. persulcatus, despite the fact that I. pavlovskyi dominates on the territory of the city and its suburbs. TEV infection was registered more often in fed ticks, in comparison with those without signs of preceding feeding. Infected specimens constituted 9.4% of 53 I. persulcatus individuals examined. In I. pavlovskyi 3.7% of 27 examined specimens were infected. In fed ticks (41 specimens of I. persulcatus and 20 I. pavlovskvi) the rates of infected specimens were higher and constituted 48.8 and 35%, respectively. In suburban forests, as well as in the city, I. persulcatus was found to attack humans more often than I. pavlovskyi. TEV infection was recorded in 12.7% of 220 unfed I. persulcatus specimens examined and in 41.6% of 142 fed individuals. In I. pavlovskyi, 6.6% of unfed and 25% of fed specimens was infected (33 unfed and 24 fed specimens were examined). Thus, in all territories examined, percent of infected specimens was significantly lower in I. pavlovskyi, and in fed ticks of both species, TEV was recorded more often.

Persistence of pathogens with short infectious periods in seasonal tick populations: the relative importance of three transmission routes

Background

The flaviviruses causing tick-borne encephalitis (TBE) persist at low but consistent levels in tick populations, despite short infectious periods in their mammalian hosts and transmission periods constrained by distinctly seasonal tick life cycles. In addition to systemic and vertical transmission, cofeeding transmission has been proposed as an important route for the persistence of TBE-causing viruses. Because cofeeding transmission requires ticks to feed simultaneously, the timing of tick activity may be critical to pathogen persistence. Existing models of tick-borne diseases do not incorporate all transmission routes and tick seasonality. Our aim is to evaluate the influence of seasonality on the relative importance of different transmission routes by using a comprehensive mathematical model.

Methodology/Principal Findings

We developed a stage-structured population model that includes tick seasonality and evaluated the relative importance of the transmission routes for pathogens with short infectious periods, in particular Powassan virus (POWV) and the related “deer tick virus,” emergent encephalitis-causing flaviviruses in North America. We used the next generation matrix method to calculate the basic reproductive ratio and performed elasticity analyses. We confirmed that cofeeding transmission is critically important for such pathogens to persist in seasonal tick populations over the reasonable range of parameter values. At higher but still plausible rates of vertical transmission, our model suggests that vertical transmission can strongly enhance pathogen prevalence when it operates in combination with cofeeding transmission.

Conclusions/Significance

Our results demonstrate that the consistent prevalence of POWV observed in tick populations could be maintained by a combination of low vertical, intermediate cofeeding and high systemic transmission rates. When vertical transmission is weak, nymphal ticks support integral parts of the transmission cycle that are critical for maintaining the pathogen. We also extended the model to pathogens that cause chronic infections in hosts and found that cofeeding transmission could contribute to elevating prevalence even in these systems. Therefore, the common assumption that cofeeding transmission is not relevant in models of chronic host infection, such as Lyme disease, could lead to underestimating pathogen prevalence.

[Transmission and circulation of tick borne pathogens (TBE and Lyme borreliosis) and the role of changing environment]

Ixodes ricinus is regarded as a species with great medical and veterinary meaning. Transmission of tick borne pathogens in mammals depends not only on systemic infection. Transmission of B. burgdorferi and tick-borne encephalitis virus in an infected organism differs, because of different location in tick, the differences in dissemination of the virus and bacteria (own motility) as well as mechanisms supporting bacterial infection. The mechanisms governing the transmission of these pathogens in nature have epidemiological importance and are essential in understanding the pathogenesis of diseases. The increase in the incidence of tick-borne encephalitis in recent years, is a marker of tick borne diseases. In the 90s, the number of cases among humans in many European countries remains at a higher level compared to the eighties. Similar observations consider to Lyme borreliosis. Natural environmental changes, mainly related to climate, as well as regional and local changes in distribution of the small rodents species, wild animals, anthropogenic factors (reforestation, drainage of swamps, increasing the reservoir of animals), and social change (increased human activities in forests, vaccinations) may have a significant impact on rates of tick-borne diseases.

Alimentary transmission of tick-borne encephalitis in the Czech Republic (1997-2008)

OBJECTIVES

Analysis of cases of tick-borne encephalitis (TBE) with confirmed food-borne transmission in patients who were unaware of tick attachment prior to the onset of illness.

MATERIAL AND METHODS

Data on laboratory confirmed cases of TBE reported in the Czech Republic (CR) in 1997-2008 were obtained from the EPIDAT system. Patient interview data were recorded in a standardised questionnaire form with multiple choices for locality (GIS) and route of transmission to be exported on a weekly basis in electronic form to a protected database of the Ministry of Health of CR. Statistical processing was conducted by ANOVA using Epi-Info CDC Atlanta and STATCALC software.

RESULTS

TBE has been recognised in CR since 1948 when, for the first time ever in Europe, the TBE virus was isolated from patients and I. ricinus ticks in two Czech and Moravian areas simultaneously (and independently of one another). TBE cases in the Czech Republic have been reported since 1971. In 1997 - 2008 the incidence ranged between 422 cases (1998) to 1029 cases (2006). Food-borne transmission of TBE was first reported in Czechoslovakia in 1954. At that time, nothing was known of the possibilities of arbovirus transmission by the food-borne route; this was discovered following the TBE epidemic of 1951 in the east Slovak town of Roznava in which 660 persons were infected, and of these, 271 were hospitalised. The source of infection was contaminated goats' milk which had been mixed into dairy milk at the local dairy and distributed without pasteurization. The risk of TBE transmission by unpasteurized goats' milk is associated with the current trend of I. ricinus tick proliferation in foothills and mountainous areas. The shift of the line of their spread from 700 m above sea level to 1200 m means that to up to 8% of the area of the CR (6300 km2) have been newly colonized by ticks. In 1997 - 2008, 64 cases of TBE were recorded in patients who reported consumption of unpasteurized goats' and dairy milk or unpasteurized sheep's milk cheese. The majority of cases involved goats' milk (36 patients, i.e. 56.3%) and sheep's milk cheese (21 patients, i.e. 32.8%). Dairy milk-borne infection was responsible for 7 TBE cases (10.9%). Of the 64 patients with food-borne TBE, 33 were men (51.6%) and 31 women (48.4%). Thirty-three cases (51.6%) occurred in family outbreaks following purchase of cheese or milk from animal breeders. Twenty-two cases (34.4%) occurred in individual patients and for 9 cases (14.0%) the data are unavailable. The highest age-specific morbidity, i.e. 1.94/100 000, was observed amongst the 5 - 9 years age-group, while in the adult age-groups the rates ranged between 0.17/100 00 (75+ years) and 0.89/100 00 (35 - 44 years). The comparison of TBE cases in child and adult age groups revealed that children in the food-borne TBE group had a 2.5 fold risk of TBE infection over adults. None of the TBE patients was vaccinated against TBE.

CONCLUSION

In 1997 - 2008, a total of 7288 cases of TBE were reported. Sixty-four (0.9%) TBE cases were food-borne. In the majority of these cases, TBE virus was transmitted by unpasteurized goats' milk and caused family outbreaks. The deciding factor in these outbreaks was an attempt to provide healthy diet to offspring.

[Modern principles of prevention of human transmitted infections]

According to information about ecology of agents of parasitic diseases with lousy-flea mechanism of contamination, mite natural diseases and experience of battle with them, we can make a conclusion: elimination of spongers in their natural environment, lousies and fleas by washing and disinfection is not effective. Alternative is implementation of insectoacaricides of new class, based on permethrins. These insectoacaricides are secure for environment and very effective towards arthopods. Method of non-termal preventing suction of arthopods is probed in military practice and other treatment-prophylaxis institutes. It is proposed to implement new insectoacaricides in form of spray cans as part of individual contrebiological drug-locker of every service man, acting in difficult epidemiological situation, caused by virus threat of lousy or flea infection, or by beforehanded provision by impregnated uniform or clothes.

Arboviruses in Italy

A brief review of the arboviruses isolated In Italy is presented and discussed. Some of the Arboviruses considered in this paper are endemic in the country and are transmitted by arthropods that play actually a role of vectors, (sand flyes, hard ticks and mosquitoes); other arboviruses, sporadically isolated, are potential agents of emerging human or zoonotic diseases.

[Epidemiological assessment of morbidity and natural foci of TBE-CEE virus infection in Transylvania]

In Romania, anthropozoonoses, and in this nosological context, human viral neuro-infections with incidental transmission by active vectors with natural foci, may be considered infectious diseases with endemic emergence. Since 1996, the form of manifestation of the epidemiological process by viral meningitis and meningoencephalitis, the etiological structure of morbidity and the problem of natural foci have required the implementation of an effective epidemiological survey strategy. This paper includes the results of an epidemiological survey and the general population seroepidemiological evaluation of acute and historic infections, identified as arboviral TBE-CEE neuro-infections.

MATERIAL AND METHOD

In the interval 1999-2006, the following aspects were studied: an endemic episode of 37 cases of TBE-CEE neuro-virus infection in a rural population. The epidemiological inquiry was conclusive for the transmission of infection by goat milk from highly tick infested animals, in a habitat with identified natural sylvatic and peridomestic foci; an endemic-epidemic state with 17 cases of TBE-CEE neuro-virus infection, occurring within a short time interval, in a rural community. Recent history revealed tick infestation from a common natural area; the size and dynamics of territorial changes in natural foci by comparing the prevalence of historic TBE-CEE infections in 41 subjects at known occupational risk, 95 subjects from the domestic habitat of former patients with TBE-CEE neuro-infection, and 172 subjects from areas adjacent to natural foci.

RESULTS

Specific serology was positive in 41.5%, 11.6%, and 5.8% of the investigated subjects (chi2 = 38.98); the prevalence of historic TBE-CEE infection in the general population was estimated at 0.6% (0.3-1.1%, CI = 95%) by the seroepidemiological investigation of a representative sample of the Transylvanian population (1669 subjects); the TBE-CEE etiology of acute viral meningitis/meningoencephalitis in the interval 2001-2006 (862 cases in the area) with a prevalence of 14.1% (10.9-17.8%, CI = 95%) of the cases, evaluated based on the etiological investigation of representative samples from 2 counties and on request from the territory (in total 397 investigated cases). Seroepidemiological tests validated by external quality control were performed using the ELISA technique, with standardized immune reagents (IgM and/or IgG specific).

CONCLUSION

Based on the epidemiological survey performed, it may be concluded that the specific infection sources and the morbidity of human TBE-CEE virus neuro-infections have an endemic emergent course and natural foci are in full territorial expansion.

Climate change cannot explain the upsurge of tick-borne encephalitis in the Baltics

Background

Pathogens transmitted by ticks cause human disease on a greater scale than any other vector-borne infections in Europe, and have increased dramatically over the past 2–3 decades. Reliable records of tick-borne encephalitis (TBE) since 1970 show an especially sharp upsurge in cases in Eastern Europe coincident with the end of Soviet rule, including the three Baltic countries, Estonia, Latvia and Lithuania, where national incidence increased from 1992 to 1993 by 64, 175 and 1,065%, respectively. At the county level within each country, however, the timing and degree of increase showed marked heterogeneity. Climate has also changed over this period, prompting an almost universal assumption of causality. For the first time, we analyse climate and TBE epidemiology at sufficiently fine spatial and temporal resolution to question this assumption.

Methodology/Principal Finding

Detailed analysis of instrumental records of climate has revealed a significant step increase in spring-time daily maximum temperatures in 1989. The seasonal timing and precise level of this warming were indeed such as could promote the transmission of TBE virus between larval and nymphal ticks co-feeding on rodents. These changes in climate, however, are virtually uniform across the Baltic region and cannot therefore explain the marked spatio-temporal heterogeneity in TBE epidemiology.

Conclusions/Significance

Instead, it is proposed that climate is just one of many different types of factors, many arising from the socio-economic transition associated with the end of Soviet rule, that have acted synergistically to increase both the abundance of infected ticks and the exposure of humans to these ticks. Understanding the precise differential contribution of each factor as a cause of the observed epidemiological heterogeneity will help direct control strategies.

[Re-evaluation of the risk areas for tick-borne encephalitis in Germany]

In the view of the authors, the present map showing the distribution of the high-risk areas for tick-borne encephalitis is no longer compatible with state of the art information. They therefore call for a re-evaluation of present definitions and a new risk map. Detection of the virus in ticks with the aid of PCR should be given the same weight as an individual clinical case. In future, a differentiation into low-risk, risk and high-risk areas should be avoided.