Host feces, olfactory beacon guiding aggregation of intestinal parasites Gasterophilus pecorum (Diptera: Gasterophilidae).

The aim of this study was to identify the aggregation sites and transmission characteristics of Gasterophilus pecorum, the dominant pathogen of endangered equines in desert steppe. Therefore, we tested with a four-arm olfactometer the olfactory response of the G. pecorum adults to the odors that have a great impact on their life cycle, and also investigated the occurrence sites of the adults in the area where the Przewalski's horse (Equus przewalskii) roam frequently during the peak period of G. pecorum infection. The results of four-directional olfactory test showed that the fresh horse feces had a stronger attraction rate on both male (50.4%) and female flies (38.2%). Stipa caucasica, the only oviposition plant where G. pecorum lay eggs, had a better attraction effect on females than that on males. And the attraction rates of S. caucasica to G. pecorum females in the early growth stage (Stipa I) and mid-growth stage (Stipa II) were 32.8% and 36.8%, respectively. In addition, the two-directional olfactory test showed that the attraction rate of males to fresh horse feces (68.90%) was higher than that to Stipa II (31.10%), and females also showed similar olfactory responses. Moreover, in our field investigation, 68.29% of G. pecorum adults were collected from around the horse feces. The results of laboratory test and field investigation implied that the location mechanism of G. pecorum aggregation for mating is related to the orientation of horse feces. The horse feces and the vicinity are the key contamination areas of G. pecorum, and it is also the areas where horses are seriously infected with G. pecorum. Those fresh feces, which gather abundant information about the host, naturally had the greatest chance of contacting with the host; G. pecorum adults create the opportunity to enter directly into the host's mouth and infect the host by laying eggs on S. caucasica, which is the most favorite plant of the host in this area. These characteristics are one of the main reasons why G. pecorum has become the dominant species under the condition of sparse vegetation in desert steppe.

Laboratory transmission potential of British mosquitoes for equine arboviruses.

BACKGROUND: There has been no evidence of transmission of mosquito-borne arboviruses of equine or human health concern to date in the UK. However, in recent years there have been a number of outbreaks of viral diseases spread by vectors in Europe. These events, in conjunction with increasing rates of globalisation and climate change, have led to concern over the future risk of mosquito-borne viral disease outbreaks in northern Europe and have highlighted the importance of being prepared for potential disease outbreaks. Here we assess several UK mosquito species for their potential to transmit arboviruses important for both equine and human health, as measured by the presence of viral RNA in saliva at different time points after taking an infective blood meal. RESULTS: The following wild-caught British mosquitoes were evaluated for their potential as vectors of zoonotic equine arboviruses: Ochlerotatus detritus for Venezuelan equine encephalitis virus (VEEV) and Ross River virus (RRV), and Culiseta annulata and Culex pipiens for Japanese encephalitis virus (JEV). Production of RNA in saliva was demonstrated at varying efficiencies for all mosquito-virus pairs. Ochlerotatus detritus was more permissive for production of RRV RNA in saliva than VEEV RNA. For RRV, 27.3% of mosquitoes expectorated viral RNA at 7 days post-infection when incubated at 21 °C and 50% at 24 °C. Strikingly, 72% of Cx. pipiens produced JEV RNA in saliva after 21 days at 18 °C. For some mosquito-virus pairs, infection and salivary RNA titres reduced over time, suggesting unstable infection dynamics. CONCLUSIONS: This study adds to the number of Palaearctic mosquito species that demonstrate expectoration of viral RNA, for arboviruses of importance to human and equine health. This work adds to evidence that native mosquito species should be investigated further for their potential to vector zoonotic mosquito-borne arboviral disease of equines in northern Europe. The evidence that Cx. pipiens is potentially an efficient laboratory vector of JEV at temperatures as low as 18 °C warrants further investigation, as this mosquito is abundant in cooler regions of Europe and is considered an important vector for West Nile Virus, which has a comparable transmission ecology.

Transmission of some species of internal parasites in horses born in 1990, 1991, and 1992 in the same pasture on a farm in central Kentucky.

Studies were conducted on transmission of natural infections of several species of internal parasites in horses born and kept on the same pasture on a farm in central Kentucky. Data for the first year (1989) of a 4 year study on this farm have been published recently. The present research represents the second (1990), third (1991), and fourth (1992) years of the investigation. The number of animals (n = 28) examined varied from eight born in 1990 to ten each born in 1991 and 1992. For each year, examination was made of one horse per month, beginning in June of the year of birth and extending through January (1990) or March (1991 and 1992) the following year. Ages of the horses at necropsy ranged from 87 to 251 days. Major parasites present and months of recovery were: bots--Gasterophilus intestinalis in the mouth September-January and in the stomach August-March; stomach worms--Trichostrongylus axei in August and November, Habronema spp. (immature) in July-November and January, and Habronema muscae in October, January, and February; ascarids--Parascaris equorum in the small intestine and lungs all months; intestinal threadworms--Strongyloides westeri in all months except February; large strongyles--Strongylus vulgaris in the large intestine in all months except July and August and in the cranial mesenteric artery in all months, and Strongylus edentatus in the large intestine in January and in the ventral abdominal wall in all months; pinworms--Oxyuris equi in June and January-March; tapeworms--Anoplocephala perfoliata in August-October and December-March; and eyeworms--Thelazia lacrymalis August-February. Yearly differences and similarities of infections in the horses are discussed. The value of this type of research is mentioned.

In vitro detection of equine arteritis virus from seminal plasma for identification of carrier stallions.

Equine arteritis virus (EAV) was readily isolated in RK-13 cell monolayers by plaque assay from seminal plasma of experimental carrier stallions when they contained high titers of virus regardless of the presence of non-viral cytotoxicity in the seminal plasma. The cytotoxicity interfered with virus isolation from seminal plasma which contained virus at titers less than 10 PFU/ml. However, it was possible to detect the virus in seminal plasma pretreated with PEG (#6000). EAV was consistently identified by RT-PCR from crude seminal plasma which contained virus at titers of more than 10(2.7) PFU/ml. In vitro detection of EAV by virus isolation supplemented with RT-PCR using seminal plasma was proved to be an effective alternative to the standard test mating as a diagnostic method for carrier stallions.

Transmission studies of Hendra virus (equine morbillivirus) in fruit bats, horses and cats.

OBJECTIVE: To determine the infectivity and transmissibility of Hendra virus (HeV). DESIGN: A disease transmission study using fruit bats, horses and cats. PROCEDURE: Eight grey-headed fruit bats (Pteropus poliocephalus) were inoculated and housed in contact with three uninfected bats and two uninfected horses. In a second experiment, four horses were inoculated by subcutaneous injection and intranasal inoculation and housed in contact with three uninfected horses and six uninfected cats. In a third experiment, 12 cats were inoculated and housed in contact with three uninfected horses. Two surviving horses were inoculated at the conclusion of the third experiment: the first orally and the second by nasal swabbing. All animals were necropsied and examined by gross and microscopic pathological methods, immunoperoxidase to detect viral antigen in formalin-fixed tissues, virus isolation was attempted on tissues and SNT and ELISA methods were used to detect HeV-specific antibody. RESULTS: Clinical disease was not observed in the fruit bats, although six of eight inoculated bats developed antibody against HeV, and two of six developed vascular lesions which contained viral antigen. The in-contact bats and horses did not seroconvert. Three of four horses that were inoculated developed acute disease, but in-contact horses and cats were not infected. In the third experiment, one of three in-contact horses contracted disease. At the time of necropsy, high titres of HeV were detected in the kidneys of six acutely infected horses, in the urine of four horses and the mouth of two, but not in the nasal cavities or tracheas. CONCLUSIONS: Grey-headed fruit bats seroconvert and develop subclinical disease when inoculated with HeV. Horses can be infected by oronasal routes and can excrete HeV in urine and saliva. It is possible to transmit HeV from cats to horses. Transmission from P poliocephalus to horses could not be proven and neither could transmission from horses to horses or horses to cats. Under the experimental conditions of the study the virus is not highly contagious.

The distribution pattern of Halicephalobus gingivalis in a horse is suggestive of a haematogenous spread of the nematode.

The majority of Halicephalobus gingivalis-infections in horses have been fatal and are usually not diagnosed before necropsy. Therefore, knowledge about the nematode and the pathogenesis of infection in horses is limited. This has resulted in an on-going discussion about the port of entry and subsequent dissemination of H. gingivalis within the host. The present case of H. gingivalis-infection in a horse was diagnosed ante mortem. Post mortem findings, the distribution pattern of H. gingivalis nematodes in the brain, a high prevalence of inflammation in close relation to blood vessels, and the presence of the nematode in multiple organs with a disseminated pattern of distribution strongly suggested a haematogenous spread of the nematode in the horse.

Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies.

Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies. Am J Epidemiol 101:36-50, 1975.-In June 1971, epidemic Venezuelan equine encephalitis (VEE) invaded the lower Rio Grande Valley in south Texas. The Boca Chica area of Cameron County was selected as a study site to investigate vertebrate involvement in the natural cycle of epidemic VEE on the basis of considerable evidence of VEE virus activity there in equines, humans, and mosquito vectors. Only one VEE virus isolation was made from 4739 wild and domestic non-equine vertebrates, although numerous equine and human VEE virus isolations were made in concurrent studies. Serologic studies indicated that VEE virus activity was far greater in large domestic animals than in wild birds, wild mammals, or reptiles. Apparently epidemic VEE virus failed to establish itself in a wild vertebrate cycle in south Texas, since VEE antibody was found only in rabbits in 1972. Eventual cessation of VEE transmission in south Texas has been attributed 1) to the elimination of equines as a source of VEE virus by death, naturally acquired antibodies, or vaccination, 2) to quarantines, 3) to mosquito control, and 4) to the failure of epidemic VEE virus to become established in the wild vertebrate population. Equines emerge as the most important vertebrate host in the amplification and spread of virus during an epidemic of VEE.

Experimental infection of horses with West Nile virus.

A total of 12 horses of different breeds and ages were infected with West Nile virus (WNV) via the bites of infected Aedes albopictus mosquitoes. Half the horses were infected with a viral isolate from the brain of a horse (BC787), and half were infected with an isolate from crow brain (NY99-6625); both were NY99 isolates. Postinfection, uninfected female Ae. albopictus fed on eight of the infected horses. In the first trial, Nt antibody titers reached >1:320, 1:20, 1:160, and 1:80 for horses 1 to 4, respectively. In the second trial, the seven horses with subclinical infections developed Nt antibody titers >1:10 between days 7 and 11 post infection. The highest viremia level in horses fed upon by the recipient mosquitoes was approximately 460 Vero cell PFU/mL. All mosquitoes that fed upon viremic horses were negative for the virus. Horses infected with the NY99 strain of WNV develop low viremia levels of short duration; therefore, infected horses are unlikely to serve as important amplifying hosts for WNV in nature.