Encapsulation of carvacrol and thymol with yeast cell wall and its repellent activity against Amblyomma sculptum and Rhipicephalus sanguineus (Sensu Lato).

The main way to avoid contact with ticks and consequently tick-borne disease is the use of synthetic repellents. The search of new repellent compounds to increase the possibilities of use in strategies controls are necessary. The present study evaluated the repellent activity of two natural terpenes carvacrol and thymol in each one two different formulation (encapsulated and nonencapsulated with yeast cell wall) against the ticks Amblyomma sculptum and Rhipicephalus sanguineus sensu lato nymphs. Nymphs of A. sculptum and R. sanguineus s.l. of a single generation were used. The vertical filter paper repellency assay were performed with different concentration of both terpenes encapsulated and nonencapsulated in yeast cell wall. The repellent concentration 50% (RC50) were calculated to each compound formulation. Both carvacrol and thymol (encapsulated and nonencapsulated), had a repellent activity against A. sculptum and R. sanguineus s.l nymphs. Amblyomma sculptum was more sensitive to nonencapsulated carvacrol (RC50 values: 0.0032 to 0.0082 mg/cm2 after 1 and 15 min) (P < 0.05), while R. sanguineus s.l. was more sensitive to encapsulated carvacrol (RC50 values: 0.00008 to 0.0035 mg/cm2 after 1 and 15 min) (P < 0.05). Among tick species, R. sanguineus s.l. was more sensitive for most compounds than A. sculptum (P < 0.05). Although with distinct repellent activities, carvacrol and thymol encapsulated can be a promising alternative to synthetic repellents against A. sculptum and R. sanguineus s.l.

Inhibition of vertebrate complement system by hematophagous arthropods: inhibitory molecules, mechanisms, physiological roles, and applications.

In arthropods, hematophagy has arisen several times throughout evolution. This specialized feeding behavior offered a highly nutritious diet obtained during blood feeds. On the other hand, blood-sucking arthropods must overcome problems brought on by blood intake and digestion. Host blood complement acts on the bite site and is still active after ingestion, so complement activation is a potential threat to the host's skin feeding environment and to the arthropod gut enterocytes. During evolution, blood-sucking arthropods have selected, either in their saliva or gut, anticomplement molecules that inactivate host blood complement. This review presents an overview of the complement system and discusses the arthropod's salivary and gut anticomplement molecules studied to date, exploring their mechanism of action and other aspects related to the arthropod-host-pathogen interface. The possible therapeutic applications of arthropod's anticomplement molecules are also discussed.

Efficacy of lotilaner against myiasis caused by Cochliomyia hominivorax (Diptera: Calliphoridae) in naturally infested dogs.

BACKGROUND: The New World screwworm fly, Cochliomyia hominivorax, is widely distributed across South America. This parasitic insect is a significant cause of primary myiasis in animals, including dogs. There is an urgent need for a rapid and efficient treatment to improve the recovery of affected animals. In the present study we evaluated the potential of lotilaner for the treatment of myiasis caused by C. hominivorax larvae in naturally infested dogs. Lotilaner belongs to the isoxazoline class of chemical compounds and is marketed as Credelio™ for use against ticks and fleas in dogs and cats. METHODS: Eleven dogs with naturally acquired myiasis were enrolled in this study based on the severity of lesions and the number of identified larvae. All animals received a single oral administration of lotilaner at a minimum dose of 20.5 mg/kg body weight. After treatment, the number of expelled larvae, live or dead, was determined at 2, 6 and 24 h, and the larval expulsion rate, larvicidal effect and overall efficacy were calculated. After 24 h, the remaining larvae were removed, counted and identified. The lesions were cleaned, and palliative treatment was administered when necessary, according to the animal's health status. RESULTS: All larvae were identified as C. hominivorax. The larval expulsion rate was 80.5% and 93.0% at 2 and 6 h post-treatment, respectively. Lotilaner showed an overall efficacy of 100% at 24 h post-treatment. CONCLUSIONS: Lotilaner demonstrated a rapid onset of action and a high efficacy against C. hominivorax. We therefore recommend lotilaner for the effective treatment of myiasis in dogs.

The gut anti-complement activity of Aedes aegypti: Investigating new ways to control the major human arboviruses vector in the Americas.

Aedes aegypti is the main urban vector of dengue virus, chikungunya virus and Zika virus due to its great dispersal capacity and virus susceptibility. A. aegypti feed on plant-derived sugars but females need a blood meal for egg maturation. Haematophagous arthropods need to overcome host haemostasis and local immune reactions in order to take a blood meal. In this context, molecules present in the saliva and/or intestinal contents of these arthropods must contain inhibitors of the complement system (CS). CS salivary and/or intestinal inhibitors are crucial to protect gut cells of haematophagous arthropods against complement attack. The present work aimed to investigate the anti-complement activity of A. aegypti intestinal contents on the alternative, classical and lectin pathways of the human complement system. Here we show that A. aegypti gut contents inhibited the human classical and the lectin pathways but not the alternative pathway. The A. aegypti gut content has a serine protease able to specifically cleave and inactivate human C4, which is a novel mechanism for human complement inactivation in haematophagous arthropods. The gut of female A. aegypti was capable of capturing human serum factor H (a negative complement modulator), unlike males. C3 molecules in recently blood-fed female A. aegypti remain in their original state, being inactivated to iC3b soon after a blood feed. A transmission-blocking vaccine using these complement inhibitory proteins as antigens has the potential to interfere with the insect's survival, reproductive fitness and block their infection by the arboviruses they transmit to humans.

Inhibition of the complement system by saliva of Anopheles (Nyssorhynchus) aquasalis.

Anopheline mosquitoes are vectors of malaria parasites. Their saliva contains anti-hemostatic and immune-modulator molecules that favor blood feeding and parasite transmission. In this study, we describe the inhibition of the alternative pathway of the complement system (AP) by Anopheles aquasalis salivary gland extracts (SGE). According to our results, the inhibitor present in SGE acts on the initial step of the AP blocking deposition of C3b on the activation surfaces. Properdin, which is a positive regulatory molecule of the AP, binds to SGE. When SGE was treated with an excess of properdin, it was unable to inhibit the AP. Through SDS-PAGE analysis, A. aquasalis presented a salivary protein with the same molecular weight as recombinant complement inhibitors belonging to the SG7 family described in the saliva of other anopheline species. At least some SG7 proteins bind to properdin and are AP inhibitors. Searching for SG7 proteins in the A. aquasalis genome, we retrieved a salivary protein that shared an 85% identity with albicin, which is the salivary alternative pathway inhibitor from A. albimanus. This A. aquasalis sequence was also very similar (81% ID) to the SG7 protein from A. darlingi, which is also an AP inhibitor. Our results suggest that the salivary complement inhibitor from A. aquasalis is an SG7 protein that can inhibit the AP by binding to properdin and abrogating its stabilizing activity. Albicin, which is the SG7 from A. albimanus, can directly inhibit AP convertase. Given the high similarity of SG7 proteins, the SG7 from A. aquasalis may also directly inhibit AP convertase in the absence of properdin.