Demonstration of regurgitation of gut content during blood meals of the tick Ornithodoros moubata. Possible role in the transmission of pathogenic agents

Mechanisms Affecting the Acquisition, Persistence and Transmission of Francisella tularensis in Ticks

Over 600,000 vector-borne disease cases were reported in the United States (U.S.) in the past 13 years, of which more than three-quarters were tick-borne diseases. Although Lyme disease accounts for the majority of tick-borne disease cases in the U.S., tularemia cases have been increasing over the past decade, with >220 cases reported yearly. However, when comparing Borrelia burgdorferi (causative agent of Lyme disease) and Francisella tularensis (causative agent of tularemia), the low infectious dose (<10 bacteria), high morbidity and mortality rates, and potential transmission of tularemia by multiple tick vectors have raised national concerns about future tularemia outbreaks. Despite these concerns, little is known about how F. tularensis is acquired by, persists in, or is transmitted by ticks. Moreover, the role of one or more tick vectors in transmitting F. tularensis to humans remains a major question. Finally, virtually no studies have examined how F. tularensis adapts to life in the tick (vs. the mammalian host), how tick endosymbionts affect F. tularensis infections, or whether other factors (e.g., tick immunity) impact the ability of F. tularensis to infect ticks. This review will assess our current understanding of each of these issues and will offer a framework for future studies, which could help us better understand tularemia and other tick-borne diseases.

The multiple roles of peroxiredoxins in tick blood feeding

Hydrogen peroxide (H₂O₂) and hydroxyl radicals (HO·) are generated through partial reduction of oxygen. The HO· are the most reactive and have a shorter half-life than H₂O₂, they are produced from comparatively stable H₂O₂ through Fenton reaction. Although controlling HO· is important and biologically advantageous for organisms, it may be difficult. Ticks are obligate hematophagous arthropods that need blood feeding for development. Ticks feed on vertebrate blood containing high levels of iron. Ticks also concentrate iron-containing host blood, leading to high levels of iron in ticks. Host-derived iron may react with oxygen in the tick body, resulting in high concentrations of H₂O₂. On the other hand, ticks have antioxidant enzymes, such as peroxiredoxins (Prxs), to scavenge H₂O₂. Gene silencing of Prxs in ticks affects their blood feeding, oviposition, and H₂O₂ concentration. Therefore, Prxs could play important roles in ticks' blood feeding and oviposition through the regulation of the H₂O₂ concentration. This review discusses the current knowledge of Prxs in hard ticks. Tick Prxs are also multifunctional molecules related to antioxidants and immunity like other organisms. In addition, tick Prxs play a role in regulating the host immune response for ticks' survival in the host body. Tick Prx also can induce Th2 immune response in the host. Thus, this review would contribute to the further understanding of the tick's antioxidant responses during blood feeding and the search for a candidate target for tick control.

Proteomic profiling of the midgut contents of Haemaphysalis flava

Scant information is available regarding the proteins involved in blood meal processing in ticks. Here, we aimed to highlight the midgut proteins involved in preventing blood meal coagulation, and in facilitating intracellular digestion in the tick Haemaphysalis flava. Proteins were extracted from the midgut contents of fully engorged and partially engorged ticks. We used liquid chromatography tandem-mass spectrometry (LC-MS/MS) analysis to identify 131 unique peptides, and 102 proteins. Of these, 15 proteins, each with at least two unique peptides, were recognized with high confidence. We also retrieved 18 unigenes from our previous published transcriptomic libraries of the midguts and salivary glands of H. flava, and inferred the primary structures of nine proteins and fragments of five proteins. There were 23 and 21 unique proteins in the midgut contents of fully engorged and partially engorged ticks, respectively. We detected 58 shared proteins in the midgut contents of both fully engorged and partially engorged ticks. Of these, seven were significantly differentially expressed between fully engorged and partially engorged ticks: actin, calmodulin, elongation factor-1α, hsp90, multifunctional chaperone, tubulin α, and tubulin β. Our results demonstrated that the proteome of the midgut contents, combined with the transcriptome of the midgut, was a viable method for the reinforcement of protein identification. This method will facilitate further study of blood meal processing by ticks, as well as the identification of clues for tick infestation control. The existence of numerous proteins detected in the midgut contents also highlight the complexity of blood digestion in ticks; this area is in need of further investigation.

Arbovirosis and potential transmission blocking vaccines

Infectious diseases caused by arboviruses (viruses transmitted by arthropods) are undergoing unprecedented epidemic activity and geographic expansion. With the recent introduction of West Nile virus (1999), chikungunya virus (2013) and Zika virus (2015) to the Americas, stopping or even preventing the expansion of viruses into susceptible populations is an increasing concern. With a few exceptions, available vaccines protecting against arboviral infections are nonexistent and current disease prevention relies on vector control interventions. However, due to the emergence of and rapidly spreading insecticide resistance, different disease control methods are needed. A feasible method of reducing emerging tropical diseases is the implementation of vaccines that prevent or decrease viral infection in the vector. These vaccines are designated ‘transmission blocking vaccines’, or TBVs. Here, we summarize previous TBV work, discuss current research on arboviral TBVs and present several promising TBV candidates.

Mechanical transfer of Theileria orientalis: possible roles of biting arthropods, colostrum and husbandry practices in disease transmission

Background

The intracellular protozoal parasite Theileria orientalis has rapidly spread across South-eastern Australia, substantially impacting local cattle industries since 2006. Haemaphysalis longicornis appears to be a biological vector in the endemic regions. Mechanical transfer of blood by biting arthropods, in colostrum or iatrogenic transmission though husbandry procedures is another possible mode of transmission. This study assesses the risk of these mechanical modes of transmission.

Methods

Blood was collected from a T. orientalis Ikeda positive Angus steer, and was inoculated into the jugular vein of 9 calves in 3 treatment groups, each with 3 animals. Calves in Group 1 received 10 ml of cryopreserved blood, while those in Groups 2 and 3 received 1 ml (fresh blood) and 0.1 ml (cryopreserved), respectively. An additional three animals remained as negative controls and the donor calf was also followed as a positive control. Blood was collected over 3 months, and analysed via qPCR for the presence of the parasite. Samples of the sucking louse Linognathus vituli were collected opportunistically from calves 5 months after inoculation and tested for T. orientalis. For the colostral transmission study, 30 samples of blood and colostrum were collected from cows at calving in an endemic herd. These samples along with blood from their calves were tested by qPCR for T. orientalis and for antibodies to the major piroplasm surface protein (MPSP).

Results

Eight of the nine inoculated calves became positive for T. orientalis. The prepatent period of these infections was inversely correlated with inoculation dose. All negative control calves remained negative and the positive control calf remained positive.

Samples of L. vituli tested positive for T. orientalis Ikeda, while some samples of colostrum were also shown to be qPCR and anti-MPSP positive. All calves in the colostral study tested qPCR negative although one was antibody-positive.

Conclusions

T. orientalis is capable of being mechanically transferred by intravenous inoculation with small volumes of blood and is detectable up to 5 months post-infection. Animals infected by this means may play a significant role in the transmission of the disease by acting as asymptomatic carriers. Other modes of blood transfer, including biting arthropods and colostral transfer are also possible modes of disease transmission.

Detection of lumpy skin disease virus in saliva of ticks fed on lumpy skin disease virus-infected cattle

Lumpy skin disease is an economically important disease of cattle that is caused by the lumpy skin disease virus (LSDV), which belongs to the genus Capripoxvirus. It is endemic in Africa and outbreaks have also been reported in the Middle-East. Transmission has mostly been associated with blood-feeding insects but recently, the authors have demonstrated mechanical transmission by Rhipicephalus appendiculatus as well as mechanical/intrastadial and transstadial transmission by Amblyomma hebraeum. Saliva is the medium of transmission of pathogens transmitted by biting arthropods and, simultaneously, it potentiates infection in the vertebrate host. This study aimed to detect LSDV in saliva of A. hebraeum and R. appendiculatus adult ticks fed, as nymphs or as adults, on LSDV-infected animals, thereby also demonstrating transstadial or mechanical/intrastadial passage of the virus in these ticks. Saliva samples were tested for LSDV by real-time PCR and virus isolation. Supernatants obtained from virus isolation were further tested by real-time PCR to confirm that the cytopathic effects observed were due to LSDV. Lumpy skin disease virus was detected, for the first time, in saliva samples of both A. hebraeum and R. appendiculatus ticks. At the same time, mechanical/intrastadial and transstadial passage of the virus was demonstrated and confirmed in R. appendiculatus and A. hebraeum.

Antigens from the midgut membranes of Ornithodoros erraticus induce lethal anti-tick immune responses in pigs and mice

Ornithodoros erraticus is an argasid tick that can transmit severe diseases such as human relapsing fever and African swine fever. In southern Europe O. erraticus lives in close association with swine on free-range pig farms. Application of acaricides for the eradication of O. erraticus from pig farms is inefficient. This is the reason why we tried to develop an anti-O. erraticus vaccine as alternative method of control. Accordingly, we were prompted to investigate the protective possibilities of a midgut membrane extract from the parasite (GME) that has not been studied hitherto. Administration of the GME with Freund's adjuvants (FAs) to pigs and mice induced a protective response able to kill 80% of the immature forms of the parasite in the first 72 h post-feeding and to reduce the fecundity of females by more than 50%. The action of the vaccine is the result of damage to the midgut wall of the argasid, and, in mice, it has been shown that this damage is mediated by activation of the complement system. In pigs, the administration of GME with alum, instead of with FAs, reduced the degree of protection. The protective antigens of the GME were expressed by all the developmental stages examined and are probably proteins from the luminal membrane of midgut epithelial cells. These antigens were seen to be more abundant in recently fed parasites than in fasting specimens, suggesting that their expression is induced after blood ingestion.