In vitro feeding of instars of the ixodid tick Amblyomma variegatum on skin membranes and its application to the transmission of Theileria mutans and Cowdria ruminatium

Artificial Feeding Systems for Vector-Borne Disease Studies

This review examines the advancements and methodologies of artificial feeding systems for the study of vector-borne diseases, offering a critical assessment of their development, advantages, and limitations relative to traditional live host models. It underscores the ethical considerations and practical benefits of such systems, including minimizing the use of live animals and enhancing experimental consistency. Various artificial feeding techniques are detailed, including membrane feeding, capillary feeding, and the utilization of engineered biocompatible materials, with their respective applications, efficacy, and the challenges encountered with their use also being outlined. This review also forecasts the integration of cutting-edge technologies like biomimicry, microfluidics, nanotechnology, and artificial intelligence to refine and expand the capabilities of artificial feeding systems. These innovations aim to more accurately simulate natural feeding conditions, thereby improving the reliability of studies on the transmission dynamics of vector-borne diseases. This comprehensive review serves as a foundational reference for researchers in the field, proposing a forward-looking perspective on the potential of artificial feeding systems to revolutionize vector-borne disease research.

In vitro feeding of all life stages of two-host Hyalomma excavatum and Hyalomma scupense and three-host Hyalomma dromedarii ticks

Ticks are blood-sucking ectoparasites and can transmit various pathogens of medical and veterinary relevance. The life cycle of ticks can be completed under laboratory conditions on experimental animals, but the artificial feeding of ticks has attracted increased interest as an alternative method. This study represents the first report on the successful in vitro feeding of all life stages of two-host tick species, Hyalomma scupense and Hyalomma excavatum, and the three-host tick Hyalomma dromedarii. The attachment and engorgement rates of adults were 84% (21/25) and 76% (19/25) for H. scupense females. For adult H. excavatum and H. dromedarii, 70% (21/30) and 34.4% (11/32) of the females attached and all attached females successfully fed to repletion. The oviposition rates of the artificially fed females were 36.4%, 57.1% and 63.1% for H. dromedarii, H. excavatum and H. scupense, respectively, with a reproductive efficiency index varying between 44.3 and 60.7%. For the larvae, the attachment and engorgement rates were 44.2% (313/708) and 42.8% (303/708) for H. dromedarii, 70.5% (129/183) and 56.8% (104/183) for H. excavatum and 92.6% (113/122) and 55.7% (68/122) for H. scupense. The attachment and engorgement rates for the nymphs were 90.2% (129/143) and 47.6% (68/143) for H. dromedarii, 66.7% (34/51) and 41.2% (21/51) for H. excavatum, and 44.1% (30/68) and 36.8% (25/68) for H. scupense. Molting rates of the immature stages varied between 71.3% (216/303) and 100% (68/68) for the larvae and between 61.9% (13/21) and 96% (24/25) for the nymphs. The successful in vitro feeding of all stages of the three Hyalomma species makes this method a valuable tool for tick research, with potential applications in studies on the pathogens transmitted by these tick species such as Theileria annulata.

Preliminary Study on Artificial versus Animal-Based Feeding Systems for Amblyomma Ticks (Acari: Ixodidae)

Hard ticks pose a threat to animal and human health. Active life stages need to feed on a vertebrate host in order to complete their life cycle. To study processes such as tick-pathogen interactions or drug efficacy and pharmacokinetics, it is necessary to maintain tick colonies under defined laboratory conditions, typically using laboratory animals. The aim of this study was to test a membrane-based artificial feeding system (AFS) applicable for Amblyomma ticks using Amblyomma tonelliae as a biological model. Adult ticks from a laboratory colony were fed in a membrane-based AFS. For comparison, other A. tonelliae adults were fed on calf and rabbit. The proportions of attached (AFS: 76%; calf/rabbit: 100%) and engorged females (AFS: 47.4%; calf/rabbit: 100%) in the AFS were significantly lower compared to animal-based feeding (p = 0.0265). The engorgement weight of in vitro fed ticks (x¯ = 658 mg; SD ± 259.80) did not significantly differ from that of ticks fed on animals (p = 0.3272, respectively 0.0947). The proportion of females that oviposited was 100% for all three feeding methods. However, the incubation period of eggs (x¯ = 54 days; SD ± 7) was longer in the AFS compared to conventional animal-based feeding (p = 0.0014); x¯ = 45 days; SD ± 2 in the rabbit and (p = 0.0144). x¯ = 48 days; SD ± 2 in the calf). Egg cluster hatching (x¯ = 41%; SD ± 44.82) was lower in the AFS than in the other feeding methods (rabbit: x¯ = 74%; SD ± 20; p = 0.0529; calf: x¯ = 81%; SD ± 22; p = 0.0256). Although the attachment, development, and the hatching of AFS ticks were below those from animal-based feeding, the method may be useful in future experiments. Nevertheless, further experiments with a higher number of tick specimens (including immature life stages) and different attractant stimuli are required to confirm the preliminary results of this study and to evaluate the applicability of AFS for Amblyomma ticks as an alternative to animal-based feeding methods.

Artificial feeding of Ornithodoros rostratus using a silicone membrane system

The in vitro feeding of ticks facilitates the conduction of studies involving the intrinsic vector-pathogen relationship, susceptibility tests, and resistance to acaricides, in addition to mimicking the use of experimental hosts. The objective of this study was to establish an in vitro feeding system using silicone membranes to supply various diets to the species Ornithodoros rostratus. Each experimental group included 130 first-instar O. rostratus nymphs. The groups were divided according to the diet provided: citrated rabbit blood, citrated bovine blood, bovine blood with antibiotics, and defibrinated bovine blood. The control group was fed directly on rabbits. Ticks were weighed before and after the feeding and monitored individually according to their biological parameters. The results of the experiment demonstrated that the proposed system was efficient in terms of fixation stimulus and satisfactory in terms of tick engorgement, which would allow the maintenance of O. rostratus colonies by using artificial feeding through silicone membranes. All diets provided were efficient for the maintenance of colonies, but the ticks that received citrated rabbit blood displayed similar biological parameters to those observed under in vivo feeding conditions.

Life History Metrics for Culex tarsalis (Diptera: Culicidae) and Culicoides sonorensis (Diptera: Ceratopogonidae) Are Not Impacted by Artificial Feeding on Defibrinated Versus EDTA-treated Blood

Artificial blood feeding is a common practice for the study and maintenance of blood-feeding arthropod colonies. Commercially purchased blood is often treated to prevent clot-formation using either mechanical or chemical means. For many hematophagous insects, the effect that different anticoagulation methods may have on life history metrics is unclear. In the current study, Culex tarsalis Coquillett and Culicoides sonorensis Wirth & Jones were fed blood treated with either mechanical (defibrination) or chemical (K2 EDTA) anticoagulation methods. Several blood feeding and life history metrics were evaluated between treatment groups including proportion blood feeding, fecundity, fertility, and mortality. No significant differences were found for any of the measured life history metrics for either species. For experiments measuring aspects of these blood feeding and life history traits, blood treated using either defibrination or K2 EDTA anticoagulants should not impact experimental outcomes.

Artificial Feeding of All Consecutive Life Stages of Ixodes ricinus

The hard tick Ixodes ricinus is an obligate hematophagous arthropod and the main vector for several zoonotic diseases. The life cycle of this three-host tick species was completed for the first time in vitro by feeding all consecutive life stages using an artificial tick feeding system (ATFS) on heparinized bovine blood supplemented with glucose, adenosine triphosphate, and gentamicin. Relevant physiological parameters were compared to ticks fed on cattle (in vivo). All in vitro feedings lasted significantly longer and the mean engorgement weight of F₀ adults and F₁ larvae and nymphs was significantly lower compared to ticks fed in vivo. The proportions of engorged ticks were significantly lower for in vitro fed adults and nymphs as well, but higher for in vitro fed larvae. F₁-females fed on blood supplemented with vitamin B had a higher detachment proportion and engorgement weight compared to F₁-females fed on blood without vitamin B, suggesting that vitamin B supplementation is essential in the artificial feeding of I. ricinus ticks previously exposed to gentamicin.

Applications of artificial membrane feeding for ixodid ticks

Ticks are obligatory hematophagous ectoparasites that feed on a large variety of vertebrates. In the laboratory, animals (mainly mice and rabbits) are used to maintain tick colonies. However, the use of animals to rear ticks can be expensive and requires dedicated animal facilities. In addition, research institutions are committed to the principle of 3Rs (Replacement, Reduction and Refinement), which encourages the use of alternatives to animals when possible. The development of artificial membrane systems has provided an alternative to animals, at least for some tick species. Over the years, different modifications in artificial feeding systems have led to new applications, including acaricide testing, tick-pathogen interaction, and novel approaches to study tick physiology. Although artificial membrane feeding still has some limitations, the method can provide numerous advantages, including the standardization of acaricide treatments under controlled conditions, an alternative to animals for tick rearing, and reduction of cost associated with animals and animal housing facilities. In this review, we summarized the evolution of tick feeding membranes and their applications over time, explaining the modifications incorporated to study tick physiology, tick-pathogen interactions, and acaricide testing.

First detection of Amblyomma variegatum and molecular finding of Rickettsia africae in Sardinia, Italy

Here we present the first detection of a male Amblyomma variegatum tick infesting a sheep on the island of Sardinia, as well as the detection of a pathogen, Rickettsia africae, in DNA extracted from this tick. The tick, the second individual of this species reported in Italy (the first one was reported in Sicily by Albanese in 1971) was collected in August 2018 from the inguinal region of an adult female sheep in a farm located near Sassari (North-West Sardinia). The tick was identified as an adult A. variegatum male under a stereomicroscope using morphological keys. A phylogenetic analysis showed that the 12S sequence clustered with that of African A. variegatum individuals and was embedded within the previously identified West African group. We tested the tick for the presence of microorganisms of the genera Ehrlichia, Rickettsia, Anaplasma, Theileria and Babesia, using published PCR protocols. The tick was found positive to Rickettsia and the obtained sequence matched at 100 % identity with R. africae. The area where the tick was detected was inspected on multiple occasions, looking for other specimens of A. variegatum, without any results. In the same period another male specimen of A. variegatum was found in Haute Corse in 2019. The authors' hypothesis is that the presence of the A. variegatum specimen is an occasional finding, probably linked to the migrating birds that cross Sardinia and Corsica from Africa during summer. Although this may have been an incidental finding, it must be considered that global warming could increase the risk of establishment of colonies of these ticks, that show a strong spreading capability. It is also important to emphasize that this tick species is a proven vector and reservoir of R. africae, an uncommon zoonotic pathogen in Italy, thus additional monitoring must be performed as the establishment of a stable population in Sardinia could represent a serious veterinary and public health issue.

Uptake and fecal excretion of Coxiella burnetii by Ixodes ricinus and Dermacentor marginatus ticks

Background

The bacterium Coxiella burnetii is the etiological agent of Q fever and is mainly transmitted via inhalation of infectious aerosols. DNA of C. burnetii is frequently detected in ticks, but the role of ticks as vectors in the epidemiology of this agent is still controversial. In this study, Ixodes ricinus and Dermacentor marginatus adults as well as I. ricinus nymphs were fed on blood spiked with C. burnetii in order to study the fate of the bacterium within putative tick vectors.

Methods

Blood-feeding experiments were performed in vitro in silicone-membrane based feeding units. The uptake, fecal excretion and transstadial transmission of C. burnetii was examined by quantitative real-time PCR as well as cultivation of feces and crushed tick filtrates in L-929 mouse fibroblast cells and cell-free culture medium.

Results

Ticks successfully fed in the feeding system with engorgement rates ranging from 29% (D. marginatus) to 64% (I. ricinus adults). Coxiella burnetii DNA was detected in the feces of both tick species during and after feeding on blood containing 10⁵ or 10⁶ genomic equivalents per ml blood (GE/ml), but not when fed on blood containing only 10⁴ GE/ml. Isolation and cultivation demonstrated the infectivity of C. burnetii in shed feces. In 25% of the I. ricinus nymphs feeding on inoculated blood, a transstadial transmission to the adult stage was detected. Females that molted from nymphs fed on inoculated blood excreted C. burnetii of up to 10⁶ genomic equivalents per mg of feces.

Conclusions

These findings show that transstadial transmission of C. burnetii occurs in I. ricinus and confirm that I. ricinus is a potential vector for Q fever. Transmission from both tick species might occur by inhalation of feces containing high amounts of viable C. burnetii rather than via tick bites.

Evaluating the effects of anticoagulants on Rhodnius prolixus artificial blood feeding

Blood-sucking insects are responsible for the transmission of several important disease-causing organisms such as viruses, bacteria, and protozoans. The hematophagous hemipteran Rhodnius prolixus is one of the most important vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. Due to the medical importance of this insect, it has been used as a study model in physiology and biochemistry since the 1930s. Artificial feeding has been recognized as a feasible and a more ethical alternative method of feeding these hematophagous insects. To prevent clotting after blood collection defibrination or treatment with anticoagulants are necessary. Although anticoagulants have been routinely used for stabilizing the collected blood, there is a gap in demonstration of the effects of using anticoagulants on the feeding and development of the hematophagous insect Rhodnius prolixus. In this study, we compared the survival rate, molting efficiency, fertility, and infection development between insects that were fed on blood containing three different anticoagulants (citrate, EDTA, and heparin). We observed that fifth instar nymphs that were fed on blood containing EDTA and citrate could not perform digestion properly, which resulted in molting inefficiency. Adult insects that were fed on EDTA-containing blood laid lower number of eggs, and also had a diminished egg hatch percentage. When we delivered T. cruzi parasites in blood containing citrate or EDTA to the insects, a lower number of parasites and metacyclic trypomastigotes was observed in the intestine compared to the group fed on heparin-containing blood. Since heparin could potentially inhibit DNA polymerase activity in DNA samples extracted from the intestine, we analyzed different heparin concentrations to determine which one is the best for use as an anticoagulant. Concentrations ranging between 2.5 and 5 U/mL were able to inhibit coagulation without severely impairing DNA polymerase activity, thus indicating that this should be considered as the range of use for feeding experiments. Our results suggest that among the three anticoagulants tested, heparin can be recommended as the anticoagulant of choice for R. prolixus feeding experiments.

Artificial blood feeders for mosquito and ticks-Where from, where to?

Mosquito and tick feeding activity represent a key threat for humans, livestock, pets and wildlife worldwide. Rearing these vectors in laboratory conditions is extremely important to investigate basic facets of their biology, vector competence, new control strategies, as well as mechanisms of pesticide resistance. However, the use of animals or humans to provide blood for hematophagous arthropod feeding poses a strict limit to these researches, due to the accidental transmission of diseases, ethical problems concerning animal welfare, as well as expensive and time-consuming animal rearing procedures. The use of devices to artificially feed arthropod vectors can importantly leverage progresses in parasitology and entomology. The aim of this review is to summarize current knowledge about artificial feeding of mosquitoes and ticks, focusing on key concepts and case studies about the design and fabrication of blood feeding devices. From a technical standpoint, the literature analyzed here showed little standardization of materials used for fabricating membrane interfaces, as well as in the strategy used to heat the "biomimetic host". In addition, a lack of uniform methods to design an architecture merging complex and realistic cues with an easy-to-assemble approach have been found. Some commercial products are available, but they are quite expensive, thus hard to reach for many laboratories, especially in developing countries. An important challenge for future research is represented by the introduction of automation and bioinspired engineered solutions in these devices, improving the effectiveness of blood-feeding systems by increasing their host-mimicking features. Automation can reduce labor costs and provide interesting solutions - in line with the 3R principle "reduce, replace and refine" - aimed to minimize the employ of experimental animals in research.

Evaluation of a semi-automated in vitro feeding system for Dermacentor reticulatus and Ixodes ricinus adults

The long feeding duration of ixodid ticks and need for regular blood changes turns the artificial feeding of ticks into a tedious process. To reduce the number of blood changes, a semi-automated system (SAS) for the artificial feeding of hard ticks was developed and evaluated. It consisted of a glass feeding reservoir that can accommodate six tick feeding chambers. A peristaltic pump was used to pump blood through the feeding reservoir, which was changed once daily. Groups of Dermacentor reticulatus and Ixodes ricinus adults were fed simultaneously in both the SAS and a conventional in vitro feeding system. In the conventional system, feeding chambers were hung inside a glass beaker filled with blood that was replaced twice daily. Dermacentor reticulatus adults fed in the SAS obtained significantly higher engorgement weights. Although engorgement rates between both systems were comparable, significantly more SAS-fed females laid fertile egg batches. The egg batch weight of SAS-fed females was also significantly higher. In contrast, the engorgement rate and fecundity of SAS-fed I. ricinus were significantly reduced in comparison to ticks fed in the conventional system. This reduction was likely to be caused by fungal infestation, which could spread between feeding chambers in the SAS. Although the SAS reduced the workload compared to the conventional feeding system and showed promising results for the in vitro feeding of D. reticulatus adults, measures to prevent fungal infestations in the SAS should be considered in future studies.

Transovarial persistence of Babesia ovata DNA in a hard tick, Haemaphysalis longicornis, in a semi-artificial mouse skin membrane feeding system

Bovine piroplasmosis, a tick-borne protozoan disease, is a major concern for the cattle industry worldwide due to its negative effects on livestock productivity. Toward the development of novel therapeutic and vaccine approaches, tick-parasite experimental models have been established to clarify the development of parasites in the ticks and the transmission of the parasites by ticks. A novel tick-Babesia experimental infection model recently revealed the time course of Babesia ovata migration in its vector Haemaphysalis longicornis, which is a dominant tick species in Japan. However, there has been no research on the transovarial persistence of B. ovata DNA using this experimental infection model. Here we assessed the presence of B. ovata DNA in eggs derived from parthenogenetic H. longicornis female ticks that had engorged after semi-artificial mouse skin membrane feeding of B. ovata-infected bovine red blood cells. The oviposition period of the engorged female ticks was 21-24 days in the semi-artificial feeding. Total egg weight measured daily reached a peak by day 3 in all female ticks. Nested PCR revealed that 3 of 10 female ticks laid B. ovata DNA-positive eggs after the semi-artificial feeding. In addition, B. ovata DNA was detected at the peak of egg weight during oviposition, indicating that B. ovata exist in the eggs laid a few days after the onset of oviposition in the tick. These findings will contribute to the establishment of B. ovata-infected H. longicornis colonies under laboratory conditions.

Rearing Ixodes scapularis, the Black-legged Tick: Feeding Immature Stages on Mice

Ixodes scapularis, the vector of Lyme disease, is one of the most important disease vectors in the eastern and Midwestern United States. This species is a three host tick that requires a blood meal from a vertebrate host for each development stage, and the adult females require a blood meal for reproduction. Larval ticks attach to their host for 3 - 5 days for feeding and drop off the host when fully engorged. This dependency on several different hosts and the lengthy attachment time for engorgement complicates tick rearing in the laboratory setting. However, to understand tick biology and tick-pathogen interactions, the production of healthy, laboratory-reared ticks is essential. Here, we demonstrate a simple, cost-effective protocol for immature tick feeding on mice. We modified the existing protocols for decreased stress on mice and increased tick feeding success and survival by using disposable cages without mesh bottoms to avoid contact of ticks with water contaminated with mice urine and feces.

Optimization of an artificial tick feeding assay for Dermacentor reticulatus

BACKGROUND

The development of standardized in vitro feeding methods for ixodid ticks has been hampered by their complex feeding behaviour and the long duration of their blood meal. In this study, we aimed to optimize several parameters for the in vitro feeding of adult Dermacentor reticulatus.

METHODS

Ticks were fed on heparinized bovine blood collected at a slaughterhouse, using a modified silicone membrane feeding assay. Effects on tick feeding and fecundity of different blood meal treatments (freezing, irradiation, addition of antibiotics), ambient conditions (increased CO₂ concentration) and phagostimulant use (addition of 2 g/l and 4 g/l glucose to the blood meal) were systematically evaluated.

RESULTS

Although fungal growth occurred more frequent in feeding units of ticks fed on defrosted blood, the attachment rate, engorgement mass and fecundity of females fed on defrosted blood did not significantly differ from that of ticks fed on fresh blood. A reduction in the fecundity of female D. reticulatus ticks was observed when ticks were fed with gamma-irradiated blood or untreated blood compared to blood treated with gentamycin. Both the engorgement mass and fecundity increased when ticks were fed at a 5% CO₂ level. A non-significant increase in the engorgement mass and engorgement rate of D. reticulatus was observed when blood was supplemented with 4 g glucose per litre compared to 2 g/l.

CONCLUSION

An artificial feeding method was adapted for the feeding of adult D. reticulatus ticks. Of all parameters tested, only the artificial feeding at 5% CO₂ levels resulted in a significant increase (P < 0.05) in the engorgement mass and fecundity of female D. reticulatus ticks. The supplementation of blood with antibiotics resulted in a significantly higher tick fecundity in comparison to ticks fed with untreated or irradiated blood.

Establishment of an Artificial Tick Feeding System to Study Theileria lestoquardi Infection

The establishment of good experimental models for Theileria sp. infection is important for theileriosis research. Routinely, infection of ticks is accomplished by feeding on parasite-infected animals (sheep, cows and horses), which raises practical and ethical problems, driving the search for alternative methods of tick infection. Artificial tick feeding systems are based mainly on rearing ticks on host-derived or hand-made artificial membranes. We developed a modified feeding assay for infecting nymphal stages of Hyalomma anatolicum ticks with Theileria lestoquardi, a highly pathogenic parasite of sheep. We compared two different membranes: an artificial silicone membrane and a natural alternative using mouse skin. We observed high attachment rates with mouse skin, whereas in vitro feeding of H. anatolicum nymphs on silicone membranes was unsuccessful. We could infect H. anatolicum nymphs with T. lestoquardi and the emerging adult ticks transmitted infective parasites to sheep. In contrast, similar infections with Rhipicephalus bursa, a representative tick with short mouth-parts that was proposed as a vector for T. lestoquardi, appeared not to be a competent vector tick species. This is the first report of an experimentally controlled infection of H. anatolicum with T. lestoquardi and opens avenues to explore tick-parasite dynamics in detail.

Infection of Immature Ixodes scapularis (Acari: Ixodidae) by Membrane Feeding

A reduction in the use of animals in infectious disease research is desirable for animal welfare as well as for simplification and standardization of experiments. An artificial silicone-based membrane-feeding system was adapted for complete engorgement of adult and nymphal Ixodes scapularis Say (Acari: Ixodidae), and for infecting nymphs with pathogenic, tick-borne bacteria. Six wild-type and genetically transformed strains of four species of bacteria were inoculated into sterile bovine blood and fed to ticks. Pathogens were consistently detected in replete nymphs by polymerase chain reaction. Adult ticks that ingested bacteria as nymphs were evaluated for transstadial transmission. Borrelia burgdorferi and Ehrlichia muris-like agent showed high rates of transstadial transmission to adult ticks, whereas Anaplasma phagocytophilum and Rickettsia monacensis demonstrated low rates of transstadial transmission/maintenance. Artificial membrane feeding can be used to routinely maintain nymphal and adult I. scapularis, and infect nymphs with tick-borne pathogens.

Effects of blood type and blood handling on feeding success, longevity and egg production in the body louse, Pediculus humanus humanus

The effects of feeding different types of human blood to human body lice, Pediculus humanus humanus L. (Phthiraptera: Pediculidae), on feeding success, longevity and numbers of eggs laid were investigated using an artificial blood-feeding system in the laboratory. No significant differences were found between lice fed on different human blood types for any of the parameters tested. However, when lice were fed on human blood of one blood type followed immediately by a different blood type, they took significantly smaller bloodmeals, their longevity was reduced and they laid fewer eggs per female than control lice that had been fed twice on the same human blood type. When lice were fed human blood that had been stored for 1-26 weeks, the quantity of blood taken, the proportion of lice that became fully engorged and lice longevity diminished gradually as the storage time of the blood increased, but there was no effect of storage time on the mean number of eggs laid per female. However, lice would not feed on 26-week-old blood. The type of anticoagulant used had a significant effect on the proportion fed, longevity and number of eggs laid per female. Generally, EDTA (ethylenediaminetetraacetic acid)-treated blood reduced longevity and the number of eggs laid per female to a greater degree than heparinized or citrated blood. Lice fed on rabbit blood took significantly larger amounts of blood, lived longer and laid a higher mean number of eggs per female than lice fed on human blood.

Quantification of Theileria parva in Rhipicephalus appendiculatus (Acari: Ixodidae) confirms differences in infection between selected tick strains

Theileria parva is the etiologic agent of East Coast fever, an economically important disease of cattle in sub-Saharan Africa. This protozoan parasite is biologically transmitted by Rhipicephalus appendiculatus (Neumann) (Acari: Ixodidae). An understanding of the vector-parasite interaction may aid the development of improved methods for controlling transmission. We developed quantitative polymerase chain reaction (qPCR) and nested PCR (nPCR) assays targeting the T. parva-specific p104 gene to study T. parva pathogenesis in two strains of R. appendiculatus that had previously been selected to be relatively more (Kiambu) or less (Muguga) susceptible to infection. Nymphs from both strains were fed simultaneously to repletion on acutely infected calves. Nymphs from the Kiambu strain showed significantly higher engorgement weights compared with Muguga strain nymphs. Immediately after engorgement qPCR confirmed that nymphal Kiambu ticks had significantly higher parasite loads at repletion than Muguga nymphs. By 12 d postengorgement, parasites were below quantifiable levels but could be detected by nPCR in 83-87% (Muguga and Kiambu, respectively) of nymphs. After the molt, adult feeding on naïve cattle stimulated parasite replication in the salivary glands. PCR detected significantly more infected ticks than microscopy, and there was a significant difference between the two tick strains both in the proportion of ticks that develop salivary gland infections, and in the number of parasites within infected salivary glands. These data confirm that although both tick strains were competent vectors, Kiambu is both a significantly more susceptible and a more efficient host for T. parva than Muguga. The mechanisms that contribute to the levels of susceptibility and efficiency are unknown; however, this study lays the groundwork for a comparison of the transcriptome of these tick strains, the next step toward discovering the genes involved in the tick-parasite interaction.

Transstadial and transovarial persistence of Babesia divergens DNA in Ixodes ricinus ticks fed on infected blood in a new skin-feeding technique

Although Babesia divergens is the the principal confirmed zoonotic Babesia sp. in Europe, there are gaps in our knowledge of its biology and transmission by the tick Ixodes ricinus. In order to reproduce the part of the parasite cycle that occurs in the vector, an in vitro animal skin feeding technique on blood containing in vitro cultivated B. divergens was developed. Parasite DNA was detected in all samples of salivary glands of nymphs and adults that had fed on parasitized blood as larvae and nymphs, respectively, indicating acquisition as well as a transtadial persistence of B. divergens. PCR performed on eggs and larvae produced by females that had fed on parasitized blood demonstrated the existence of a transovarial transmission of the parasite. Gorging B. divergens infected larvae on non-infected gerbils showed persistance of the parasite over moulting into the resulting nymphs. These results indicate that the parasitic stages infective for the vector (i.e. the sexual stages) can be produced in vitro. To our knowledge, this is the first report of artificial feeding of I. ricinus via membrane as well as in vitro transmission of B. divergens to its vector. The opportunities offered by the use of such a transmission model of a pathogen by I. ricinus are discussed.

Experimental infection of Ixodes scapularis larvae (Acari: Ixodidae) by immersion in low passage cultures of Borrelia burgdorferi

We describe a procedure for the introduction of Borrelia burgdorferi, the spirochetal agent of Lyme disease, into larvae of the tick vector Ixodes scapularis. Internalized spirochetes were observed in larvae examined after 15 or 45 min immersion at 32 degrees C in liquid culture suspensions of low passage B. burgdorferi strain B31. Larval ticks immersed in low passage strain B31 were able to feed to repletion on white-footed mice. Midguts of larvae contained many spirochetes 1 wk postengorgement, while larvae incubated with high passage strain B31 were free of detectable spirochetes at the same interval. Larvae incubated with low passage strain B31 were competent to transmit the pathogen to mice, as shown by serology, reisolation of B. burgdorferi from mice, and xenodiagnosis. Ticks maintained the infection transstadially to the nymphal stage and transmitted the infection to naive mice, replicating an essential aspect of natural infection. This method requires no special equipment and allows artificial infection of large numbers of ticks at the larval stage. It will facilitate studies of the contribution of specific B. burgdorferi genetic loci to tick colonization.

Infection and transovarial transmission of rickettsiae in Dermacentor variabilis ticks acquired by artificial feeding

In this study we examined the efficiency of an in vitro feeding technique using glass microcapillaries as a method of establishing rickettsiae-infected lines of ticks. To quantify the volume ingested by ticks during microcapillary feeding, the incorporation of radiolabeled amino acids in tick gut and hemolymph was calculated. Fifteen of 18 ticks consumed between 0.06 and 6.77 microl. However, ingestion of fluid was not correlated to weight gain during capillary feeding. Uninfected and partially fed laboratory-reared female Dermacentor variabilis ticks were exposed to either Rickettsia montana- or Rickettsia rhipicephali-infected Vero cells via microcapillary tubes, returned to rabbit hosts, and allowed to feed to repletion. All tissues collected from ticks allowed to feed overnight on rickettsiae-infected fluids were found to be infected when examined by IFA. When rickettsiae-infected and uninfected capillary-fed ticks were allowed to feed to repletion and lay eggs, no significant differences in mean engorgement weight or fecundity was observed. When we assessed the efficiency of transovarial transmission of rickettsiae by ticks that imbibed rickettsiae-infected cells by polymerase chain reaction (PCR) and IFA, infection was detected by PCR in the eggs from 85% of the ticks exposed to R. montana and 69% of the ticks exposed to R. rhipicephali. Rickettsial genes were not amplified in samples of the uninfected controls. Examination by IFA of egg samples from females exposed to rickettsiae-infected cells identified rickettsiae in 100% of the samples tested, while the uninfected controls were negative.

Infection of Ixodes scapularis (Acari: Ixodidae) with Borrelia burgdorferi using a new artificial feeding technique

To study interactions between Ixodes scapularis (Say) and Borrelia burgdorferi, an artificial feeding system was refined to allow controlled manipulation of single variables. The feeding system uses a mouse skin mounted on a water-jacketed glass membrane feeder. I. scapularis were infected using either BSK-H-cultured B. burgdorferi spirochetes or a B. burgdorferi-infected mouse skin as the source of spirochetes. Sixty-six percent of nymphs successfully fed to repletion using the artificial feeding systems with at least 75% of nymphs becoming infected with B. burgdorferi. Strain B31 B. burgdorferi spirochetes from passages 2-17 were equally infectious to nymphal ticks. At concentrations of one spirochete per microliter, 12% of nymphs acquired infection and 14 and 100 spirochetes per microliter resulted in 50 and 100% infection rates, respectively. Eighty-nine percent of nymphs fed by artificial feeding molted to the adult stage. When subsequently fed as adults, these I. scapularis successfully transmitted infectious B. burgdorferi spirochetes to mice.

Amblyomma americanum: specific uptake of immunoglobulins into tick hemolymph during feeding

The passage of immunoglobulins in the blood meal into hemolymph prompts development of vaccines against internal antigens of ticks, but little is known about kinetics and specificity of the immunoglobulin uptake. We used capillary feeding of adult Amblyomma americanum hard ticks to introduce compounds into the midgut and then examined the hemolymph after various times for their presence and concentration. Immunoglobulins of different sources, albumin, choramphenicol acetyltransferase, inulin, and mannitol were labeled with (125)I, (14)C, or biotin. With the exception of the carbohydrate inulin, all the compounds entered the hemolymph of tick during capillary feeding. The small molecule mannitol had the highest rate of entry at 9% after 6 h. Among proteins, the entry of immunoglobulin G (IgG) of different species into the hemolymph was greater at 6% after 6 h than for the smaller proteins albumin or choramphenicol acetyltransferase at 1 and 3%, respectively. The entry of denatured IgG was equal to that of nondenatured protein. There was no evidence of degradation of the IgG or of its binding to cells once it entered the hemolymph. A monoclonal IgG antibody labeled with biotin entered the hemolymph and retained its ability to bind to its specific antigen in an immunoassay. Although different proteins entered the hemolymph after capillary feeding, there was evidence of a specific mechanism for immunoglobulin uptake.

Attempts to feed Amblyomma variegatum ticks on artificial membranes

Feeding jars were used to feed nymphs of Amblyomma variegatum on blood of goats or cattle. Sterile blood was collected daily or weekly (kept at 4 degrees C or frozen until use), with addition either of heparin alone or of heparin and antibiotics/fungicide or of heparin, adenosine triphosphate and glutathione. Membranes were made of a thin (0.12-0.32 mm) film of silicone mastic. Blood in the jars was replaced twice a day, and reached a temperature of 39 degrees C in a waterbath before it became available to the ticks. Attachment of nymphs was stimulated by dropping on the membrane fresh goat hair and squamae collected close to prefed males, skin washing and natural pheromone extracts. Using these devices, attachment of nymphs is rapid and intense (68%). Their body mass when engorged and the molting success, were lower than that of naturally fed ticks. Furthermore, the proportion of engorging ticks was usually much less and the length of the blood meal was much longer than of naturally fed ticks. The best results were obtained with fresh goat blood or cattle blood with antibiotics. Further developments are needed before this method can be used routinely.

Establishment of Boophilus microplus infected with Babesia bigemina by using in vitro tube feeding technique

The in vitro tube feeding technique is used to establish a laboratory colony of Boophilus microplus infected with Babesia bigemina. Pre-fed engorged female ticks offered 2 x 10(4) and 2 x 10(5)/ml of B. bigemina infected bovine red blood cells (RBC) showed sporokinetes in the haemolymph smear sample, and positive signals for B. bigemina in polymerase chain reaction (PCR). Larvae laid from the ticks offered 2 x 10(5)/ml of B. bigemina infected RBC showed evidence for B. bigemina infection in microscopic method and PCR. While larvae laid from the ticks offered 2 x 10(4)/ml of B. bigemina infected RBC showed positive for B. bigemina in only PCR. The females offered 2 x 10(3)/ml B. bigemina infected RBC and their larvae did not show positive evidences for B. bigemina infection. It is thought that the in vitro tube feeding technique can be a convenient method to study the relationship between ticks and tick-borne pathogens. It is also suggested that the superior sensitivity of PCR compared to the microscopic method in detection of B. bigemina from the tick sample, especially in larvae.

Alternatives to animal experimentation in parasitology

In parasitology, several measures can contribute to the aims of 3R (Reduction, Refinement and Replacement of animal experimentation). These include legal regulations, international guidelines for evaluating antiparasitic drugs, the refinement of animal models for parasitic infections, cryopreservation and cultivation of parasites in vitro or in chicken eggs, the maintenance of arthropods by artificial feeding, and the use of immunological and molecular in vitro techniques (e.g. the production of recombinant antigens for vaccines). Considerable progress has been achieved in the development of alternative techniques but both their standardisation and validation are not far advanced. A wider acceptance and use of alternative methods will only be achieved if research can offer economic alternatives that are as effective and reliable as animal experiments. Great efforts are needed for further progress.

Artificial feeding of ixodid ticks

Ixodid ticks are economically important as they cause direct damage to livestock and are vectors of several pathogens that cause diseases in humans and animals. Some of the important tick-borne pathogens of livestock are Theileria parva, T. annulata, Babesia bigemina, B. bovis, Anaplasma marginale and Cowdria ruminantium. These pathogens are responsible for causing enormous losses in livestock. Identification of factors that influence transmission and development of these pathogens in ticks will greatly facilitate development of rational strategies for control of tick-borne diseases. This research has been hampered by the lack of suitable artificial feeding methods. In this paper, Sam Waladde, Aian Young and Subhash Morzaria review recent developments in the artificial feeding of ixodid ticks and evaluate how this method can potentially be exploited. They use an example the transmission of an important livestock pathogen, T. parva, by Rhipicephalus appendiculatus.

Optimization of the in vitro feeding of Rhipicephalus appendiculatus nymphae for the transmission of Theileria parva

An apparatus for artificial feeding of Rhipicephalus appendiculatus nymphae was modified to improve feeding performance. Heparinized blood was supplied above a treated artificial membrane while the ticks attached below on its undersurface. The feeding apparatus was incubated at 37 degrees C in an atmosphere of 3% CO2 concentration and a relative humidity of 75-80%. Under these conditions, 91% of the engorged nymphae attained a mean weight of 6-11 mg, and an average of 93% of those nymphae moulted into adults. When this system was used to feed nymphal ticks on blood infected with Theileria parva piroplasms, the mean prevalence of infection in the resultant female and male ticks was 86% and 54%, respectively. The feeding performance and T. parva infection levels were comparable to those of nymphal ticks fed on the blood donor cattle. The apparatus used in this study has potential for modification to suit the artificial feeding needs of other species of ixodid ticks and for use in investigations to examine other tick/pathogen relationships.

The life-cycle of the bont tick Amblyomma hebraeum in vitro

The life-cycle of the hard tick Amblyomma hebraeum was completed in vitro by feeding all life-stages of the tick through silicone membranes on bovine blood from an abattoir. Ticks were placed in a simple feeder membranes on bovine blood from an abattoir. Ticks were placed in a simple feeder consisting of a honey jar containing the blood with a glass tube insert (o.d. 42 mm) across the end of which the membrane was stretched. This feeding unit was held in a water bath (38 degrees C). Larvae and nymphs fed on a membrane (< 90 microns thick) made of silicone reinforced with Kodak lens cleaning paper, and adults on a silicone membrane (0.5 mm thick) reinforced with Terylene netting. To control microbial growth, gentamicin (5 micrograms/ml) and nystatin (100 i.u./ml) were added to the weekly open-collected blood, which was manually defibrinated. The blood was changed twice daily for nymphs and three times for adults and larvae. Attachment of ticks was induced with combinations of host hair, tick faeces, a bovine pelage extract and a synthetic aggregation-attachment pheromone mixture. The in vitro life-cycle started with unengorged "natural" adults, which had moulted from nymphs fed on steer. The life-cycle closed with unengorged, first in vitro generation adults which had moulted from nymphs fed in vitro. Although the feeding and development of larvae and nymphs were similar to in vivo controls, females fed and developed poorly in vitro. The toxicity of the systemic acaricide Ivermectin for nymphs of A. hebraeum was confirmed using the in vitro feeding method.

Transmission of Theileria parva to cattle by Rhipicephalus appendiculatus adults fed as nymphae in vitro on infected blood through an artificial membrane

A technique is described for the efficient feeding of Rhipicephalus appendiculatus nymphae on cattle blood through an artificial membrane bearing tactile and olfactory stimuli. The effect of four anticoagulation methods on the feeding of nymphae was compared and heparinized blood was found to be the most efficacious, followed by defibrinated blood. Blood treated with acid citrate dextrose (ACD) or ethylenediamine tetraacetate (EDTA) inhibited nymphal feeding. Nymphae fed on heparinized and defibrinated blood obtained engorgement weights within the range of ticks fed on mammalian hosts and they subsequently moulted and fed normally as adults and produced viable eggs. Nymphae fed on membranes using either defibrinated or heparinized blood infected with Theileria parva piroplasma developed salivary gland infections as adult ticks and transmitted East Coast fever (ECF) to susceptible cattle. There were indications that T. parva-infected defibrinated blood was not as infective to the feeding nymphae as the infected heparinized blood. When T. parva-infected heparinized blood was used to feed nymphae through membranes in two experiments, it was found that the infections in the resultant adult ticks could be comparable to those of nymphae fed on donor cattle, but were usually lower. The membrane feeding technique will enable the study of factors affecting the tick and T. parva transmission without the complication of host/T. parva interactions and could be useful for both tick maintenance and Theileria parasite isolation and maintenance.