Onchocerca ochengi acquisition in zebu Gudali cattle exposed to natural transmission: parasite population dynamics and IgG antibody subclass responses to Ov10/Ov11 recombinant antigens

Ngaoundere Gudali zebu cattle naturally exposed to Simulium damnosum s.l. and Culicoides spp. bites were examined during 4 years for O. ochengi adult worm acquisition, Onchocerca ochengi and Onchocerca gutturosa skin microfilaria dynamics, and IgG1 and IgG2 antibody subclass responses. Eleven animals acquired a total of 465 O. ochengi nodules (average of 17 per female and 72 per male). The O. ochengi nodule load was highly variable in individual animals and exacerbated in mature male cattle. Three patterns of acquisition of O. ochengi (resistant to new infestation, early susceptibility and late susceptibility), not associated with Simulium biting intensity (P > 0.05), were distinguished. The minimum prepatent periods for O. ochengi nodules, O. ochengi microfilariae and O. gutturosa microfilariae were 10, 20 and 21 months, respectively. The O. ochengi microfilaria density significantly (P < 0.001) increased with age, was higher in young mature bulls than female animals (P < 0.001) and finally reached highest levels (P < 0.005) during the dry season. Antibody responses to Ov10/Ov11 recombinant O. volvulus antigens were predominantly of the IgG1 subclass. High levels of this subclass (not IgG2) observed in new born calves declined to almost zero levels at the age of 5-8 months but IgG1 levels significantly increased (P < 0.05) with age subsequently during patency. Put together the acquisition and accumulation of O. ochengi parasites in zebu cattle, apart from being season, sex (gender) and host age associated, may also suggest a density-dependent regulation of parasite establishment in a proportion of the exposed population.     

Simulium jenningsi Malloch (Diptera: Simuliidae): a vector of Onchocerca lienalis Stiles (Nematoda: Filarioidea) in New York

Biting flies were collected from the umbilical areas of Onchocerca lienalis-infected cattle in New York (state) from June through September of 1980. Of the 766 flies collected, 705 were Simulium jenningsi. Microfilariae were detected in the midguts of 37 (50%) of 73 females dissected immediately after the flies had fed. The mean number of larvae per positive fly (fly with microfilariae) was 15.2. Third-stage larvae were recovered from 25 (21.9%) of 114 S jenningsi dissected 8 to 13 days after they had fed on the infected cattle; the mean number of 3rd-stage larvae per positive fly was 3.5. Dissections of flies performed on days 1 through 7 after feeding yielded various numbers of 1st and 2nd-stage larvae from the thoracic muscles. Ovarian dissections performed on 304 S jenningsi attacking cattle indicated an overall parous rate of 58%. Naturally occurring infections with filarial larvae indistinguishable from O lienalis were found in 7.3% of the parous females. Three of these flies, or 1.7% of the parous collection, harbored 3rd-stage larvae. The onset of naturally occurring filarial infections in the population of S jenningsi coincided with a peak in the parous rate in late June. Thereafter, filarial infections were generally detected when the parous rate was above 50%.     

Seasonal prevalence of bovine trypanosomosis in a tsetse-infested zone and a tsetse-free zone of the Amhara Region, north-west Ethiopia

During a period of four consecutive years, trypanosomosis surveys were conducted in a tsetse-infested and tsetse-free area of the Amhara Region of north-west Ethiopia. In each study area randomly selected communal cattle were sampled and their blood was investigated using parasitological diagnostic methods. At the same time the population of biting flies was sampled. The monthly average prevalence of trypanosome infections in cattle did not differ significantly between study areas. In both study areas, the prevalence of trypanosome infections was highest during the long rainy season. Trypanosome infections were mainly due to Trypanosoma vivax and they significantly reduced the average packed cell volume and the body condition of the animals. The monthly prevalence of infection was correlated with the density of biting flies, such as Tabanidae and Stomoxys spp., in the preceding month suggesting an important role of mechanical transmission in the epidemiology of trypanosomosis in both areas.     

Biting flies and Trypanosoma vivax infection in three highland districts bordering lake Tana, Ethiopia

An epidemiological study was conducted to determine the prevalence of trypanosomosis in cattle, small ruminants and Equidae, and to identify biting flies; potential mechanical vectors of trypanosomes in the three districts of Bahir Dar Zuria, Dembia and Fogera, bordering lake Tana, Ethiopia. About 1509 cattle, 798 small ruminants and 749 Equidae were bled for the prevalence study using the buffy-coat method and the measurement of the hematocrit value. Sixty-six NGU and 20 monoconical traps were deployed for the fly survey. The results indicated the presence of trypanosomes in 6.1% (92/1509) of the cattle with a maximum during the late rainy season (9.6%) than the early dry season (3.6%) at Fogera district. Prevalence at the district level varied from 4% to 9.6%. Only one sheep (1/122) and one goat (1/676) were found positive for T. vivax-like trypanosomes and none of the Equidae was positive. All the trypanosomes encountered in cattle belong to the single species of T. vivax. The PCV was negatively associated with detection of T. vivax (21.6% in infected versus 25.4% in non-infected cattle). A total of 55,398 biting flies were caught of which 49,353 (89.08%) belong to Stomoxys, 4715 (8.51%) to horse flies and 1330 (2.4%) to Chrysops species. There was no tsetse fly. Species identification has indicated the presence of Atylotus agrestis, Chrysops streptobalia, Stomoxys calcitrans, S. nigra, S. pulla, S. pallida, S. sitiens, S. taeniata, S. uruma, Haematopota lasiops and Hippobosca variegata. The overall apparent density was 214.7flies/trap/day. Seasonal comparison showed higher fly catches in the late rainy season than the early dry season. This study indicated that T. vivax infections culminate in cattle at the same time as mechanical vectors such as Stomoxys sp. and Atylotus agrestis. Therefore, attention towards T. vivax infection in cattle is essential to control the impact of the disease on productivity. A further study on biting flies is recommended.     

Role of insects in the transmission of bovine leukosis virus: potential for transmission by stable flies, horn flies, and tabanids

The ability of stable flies (Stomoxys calcitrans), horn flies (Haematobia irritans), and tabanids (Diptera: Tabanidae) to transmit bovine leukosis virus (BLV) was investigated. Stable flies and horn flies were fed on blood collected from an infected cow, and the flies' mouthparts were immediately removed, placed in RPMI-1640 medium, ground, and inoculated into sheep and calves. Infection of sheep occurred with mouthparts from as few as 25 stable flies or 25 horn flies. However, sheep were not infected when removal of stable fly mouthparts was delayed greater than or equal to 1 hour after blood feeding. Infection of calves occurred after inoculation of mouthparts removed immediately after feeding from as few as 50 stable flies or 100 horn flies. Infected blood, applied by capillary action to the mouthparts (labella) of 15 deer flies (Chrysops sp) and a single horse fly (Tabanus atratus) caused infection in each of 2 sheep. Infection did not occur in 2 calves inoculated daily for 5 days with mouthparts from 50 horn flies collected after feeding on a BLV-infected steer. Four calves receiving bites from 75 stable flies interrupted from feeding on a BLV-positive cow also were not infected. Seronegative cattle held for 1 to 4 months in a screened enclosure with positive cattle in the presence of biting flies were not infected with BLV. The feeding behavior of each insect is discussed to assess their potential as vectors of BLV.     

Onchocerca gutturosa and Onchocerca lienalis in cattle: variation in length of microfilariae by site of recovery

Dermal microfilariae recovered from specimens obtained from umbilical and cervical sites of cattle infected with adult Onchocerca gutturosa alone or with adults of O gutturosa and O lienalis were measured and compared with uterine microfilariae obtained directly from gravid female worms of each species. Uterine microfilariae of O gutturosa were longer than dermal microfilariae obtained from cattle harboring only adults of O gutturosa. Dermal microfilariae were recovered from umbilical and cervical sites in these cattle. Those found at the cervical site had lengths equal to or greater than lengths of microfilariae recovered from the umbilical site. There was a significant (P less than 0.0001) shift in length across populations of microfilariae of O gutturosa from various sites in its bovine host, with a progressive decrease in length between microfilariae recovered from the worm's uterus, microfilariae from the cervical dermis, and microfilariae from the umbilical dermis, respectively. A similar direct comparison was not possible for microfilariae of O lienalis, because none of the cattle was infected with only adult worms of this species. In an indirect comparison, microfilariae of O lienalis were identified at the umbilicus, but their presence in the cervical region could not be determined unequivocally because of confounding of microfilariae length by concurrent infection with O gutturosa. Uterine microfilariae from O lienalis were longer than uterine microfilariae of O gutturosa, although a degree of overlap in the range of measurements existed between species.     

Distribution of microfilariae of Onchocerca lienalis and Onchocerca gutturosa in the skin of cattle in Germany and their development in Simulium ornatum and Culicoides nubeculosus following artificial infestation

Onchocerca microfilariae were isolated form the umbilicus and neck of 438 cow hides at the abattoir in Tübingen, F.R.G. The overall Onchocerca infection rate was 40.4%. The presence of Onchocerca lienalis and O. gutturosa microfilariae, which are difficult to distinguish by morphological criteria, was retrospectively demonstrated after artifically infesting Simulium ornatum and Culicoides nubeculosus and identifying the infective larvae recovered. Nine of 16 samples of umbilical microfilariae fed to C. nubeculosus through a latex membrane developed to O. gutturosa third stage larvae (L3). Six of seven umbilical samples injected into the thorax of S. ornatum yielded O. lienalis L3. In six infestation trials in which microfilariae were introduced both into S. ornatum and C. nubeculosus, O. lienalis L3 were recovered exclusively from simuliids, while O. gutturosa L3 developed only in midges. Of six umbilical skins tested by cross-infestation, one contained exclusively O. gutturosa microfilariae, four only O. lienalis microfilariae and one was infected with both species. Developmental success of O. lienalis microfilariae to L3 in S. ornatum following intrathoracic injection was 22% of the mean inoculum. O. gutturosa microfilariae, ingested by C. nubeculosus through a latex membrane, developed to L3 at a rate of 2.3% of the mean microfilarial uptake.     

An investigation for seasonal trends in bovine leukemia virus infection

Monthly incidence rates for the detection of bovine leukemia virus (BLV) infection were calculated for a 15-month period for cattle over 12 months of age in a 200-cow dairy herd. Detection of BLV infection was based on the presence of persisting antibodies as measured by agar-gel immunodiffusion using the glycoprotein-51 antigen. A non-parametric procedure was used to examine 6-month trends in cumulative monthly incidence rates. Over the 15-month study, 25 heifers were detected as becoming infected with BLV after 12 months of age. No differences were found between the 12 monthly incidence rates (p = 0.77). Cumulative incidence rates between June and September (the fly season) were not higher than those for any other 6-month period (p = 0.29). Similarly, there was no evidence that BLV infection was transmitted during artificial insemination (p = 0.18) or during routine vaccination procedures (p = 1.0). Cumulative rates for a period corresponding to exposure of heifers to the dry herd were excessively high (p = 0.01). These findings suggest that transmission of BLV infection in the cattle studied was associated with close physical contact between susceptible and infected cattle, and not with biting flies, artificial insemination, or vaccination procedures.     

Evaluation of transmission of bovine viral diarrhea virus (BVDV) between persistently infected and naive cattle by the horn fly <Emphasis Type="Italic">(Haematobia irritans)</Emphasis>

Identifying reservoirs and transmission routes for bovine viral diarrhea virus (BVDV) are important in developing biosecurity programs. The aim of this study was to evaluate BVDV transmission by the hematophagous horn fly (Haematobia irritans). Flies collected from four persistently infected cattle were placed in fly cages attached to principal (n?=?4) and control (n?=?4) BVDV-naïve calves housed individually in isolation rooms. Flies were able to feed on principal calves, but a barrier prevented fly feeding from control calves. Flies were tested for BVDV by RT-PCR and virus isolation at time of collection from PI cattle and after 48 h of exposure on BVDV-naïve calves. Blood samples were collected from calves and tested for BVDV infection. Virus was isolated from fly homogenates at collection from PI animals and at removal from control and principal calves. All calves remained negative for BVDV by virus isolation and serology throughout the study. Bovine viral diarrhea virus may be detected in horn flies collected from PI cattle, but horn flies do not appear to be an important vector for BVDV transmission.     

Evaluation of a mixture of trimethoprim and sulphaquinoxaline for the treatment of poultry: safety and palatability studies

Ear tags containing 8.5 per cent w/w cypermethrin gave almost complete control of the biting muscid, Haematobosca stimulans. Protection afforded against nuisance flies was more variable; generally a 70 to 80 per cent reduction of headfly, Hydrotaea irritans, and a 60 to 70 per cent reduction of Morellia simplex. Ear tags containing 8.5 per cent fenvalerate also gave significant protection against biting and nuisance flies. Spraying with 500 ppm cyhalothrin or 1000 ppm cypermethrin afforded complete protection against H stimulans and reduced the burden of H irritans by approximately 90 per cent and M simplex by 80 to 90 per cent. A two week interval between treatments is suggested although this could be extended where weather conditions were favourable to the retention of insecticide on the skin or fly challenge was low. No significant increase in liveweight gain was associated with fly control. Treated animals were less disturbed when grazing and were more easily handled, especially when milking.     

Seasonal differences in the incidence of infection with Fasciola gigantica in cambodian cattle

Farmer's cattle were treated with triclabendazole and used as tracer animals to detect new infections with Fasciola gigantica in three villages located on the bank of the Bassac River (a major tributary of the Mekong River) and in a fourth village located on farmland away from the river, from April 1999 until January 2001. The month of infection was estimated by subtracting 4 months from the date when eggs of F. gigantica were detected in faeces. Farmers were interviewed each month to record the nature of the agricultural and animal husbandry activities that occurred during the previous month, especially events that might have exposed cattle to infection with F. gigantica. Results support the conclusions that infection of cattle in riverbank villages acquired from about August or September until November originated from herbage and water in irrigation canals and dams on the riverbank, and that the progressively increasing monthly incidence from December until April (up to 87% per month in April 2000) was derived from herbage and water in recently harvested rice fields and lakes adjacent to the riverbank. The abrupt cessation of new infection in riverbank villages in May coincided with flooding of low-lying land, the movement of cattle to land above flood height on the riverbank, and a change of diet to dry-land crop residues, stored dry rice stalks, and herbage and water that were unlikely to contain metacercariae. It was concluded that snails in dams and canals on the riverbank became infected with F. gigantica after cattle were moved to the riverbank in May, and cercariae shed from these snails provided the new infections that occurred in cattle in August and September. In the village located away from the river, infection of cattle between September and March coincided with the rice harvest, supporting the conclusion that feeding of fresh rice stalks and stubble after the rice was harvested was the main source of infection. The low monthly incidence observed (up to 6.4% per month) was consistent with the hypothesis that snails did not survive in the dry rice fields between crops and that few snails would have been available from the small number of aquatic refuges that persisted through the dry season to recolonize rice fields during the wet season. Between April and August there was no opportunity for new infection because cattle were fed forage from around houses and headlands, and on dry-land crop residues and stored dry rice stalks. Control of fasciolosis was proposed using a single treatment of cattle with triclabendazole in riverbank villages in May when cattle were moved to the riverbank, and after harvest of the last rice field in villages located away from the river.     

Ocular onchocercosis in dogs: aberrant infection in an accidental host or lupi onchocercosis?

Four adult dogs that had spent their entire life in Hungary, were found to be infected with filaroid nematodes of the genus Onchocerca. The morphology and location of the parasites as well as pathological lesions were similar to those described earlier in the one Hungarian and five US dogs. Only moderate morphological differences were noted between the adults of Onchocerca sp. infecting dogs and O. volvulus of man or O. lienalis of cattle. Nevertheless, the morphology of microfilariae of Onchocerca from dogs is unique within the genus. Their length was less than half the length of microfilariae of other Onchocerca spp. known so far. In addition to size differences, several characteristic morphological features were observed. The unsuccessful attempt to infect dogs with O. lienalis, the absence of O. volvulus and O. lienalis in endemic regions of canine onchocercosis, the different size, morphology, and location of the adults in dogs and cattle, the exceptionally small size and unique morphology of microfilariae of Onchocerca of canids indicate that a distinct species might be responsible for canine onchocercosis. Since the larval concentration in the skin was high (50-3600 microfilariae g(-1)) in all affected dogs, the diagnosis prior to surgical removal of worm nodules can be based on the examination of a small skin snip collected from the head or abdominal region. Infections in dogs may provide a model to study human onchocercosis, therefore, further studies are encouraged on the feasibility of experimental infection of dogs with this Onchocerca species.     

Epidemiology of wildebeest-derived malignant catarrhal fever in South Africa: inability to transfer the disease with an African face fly Musca xanthomelas (Diptera: Muscidae)

Under experimental conditions an African face fly (Musca xanthomelas) preferred to feed on cattle dung when provided with a choice of 3 different meals namely sucrose, cattle dung and blood. Flies starved overnight fed well on the eyes of cattle and rabbits, but were reluctant to feed again within 2 h after being allowed to feed on cell culture medium or on the eyes of wildebeest, and when they did feed, they preferred to feed on the external side of the eyelids and on the coagulated material in the medial canthus of the eye. Under field conditions flies were rarely seen to feed on the eyes of immobilized wildebeest. Although M. xanthomelas became infected with Alcelaphinae herpes virus 1 (AHV-1) when they fed on infective wildebeest tears or cell culture medium, they lost the virus within 5 h, and recovery of infective AHV-1 particles from regurgitated cell culture medium was limited to the first 30 min after feeding. AHV-1 could not be transmitted by flies to cattle or rabbits. The failure to transfer the virus with flies can be ascribed to their reluctance to feed on cattle or rabbits shortly after they have consumed a protein rich meal, the rapid inactivation of ingested virus and the relatively high titre of virus necessary to infect cattle via the ocular route. Furthermore, it is believed that under natural conditions flies that have emerged from cattle dung will be inclined to stay with cattle where food is freely available.(ABSTRACT TRUNCATED AT 250 WORDS)     

The transmission of mixed Trypanosoma brucei brucei/T. congolense infections by tsetse (Glossina morsitans morsitans)

Laboratory experiments and field observations clearly show that tsetse flies can be carriers of mixed trypanosome infections. Question remains how easy it is for the tsetse fly to acquire such a mixed infection during the first bloodmeal. This is of particular importance in the epidemiology of Trypanosoma brucei s.l., often a cryptic infection and difficult to transmit to non-teneral tsetse flies. To determine the transmission rate of T. brucei as part of a mixed infection, teneral Glossina morsitans morsitans were fed once on cattle with a mixed (Trypanosoma brucei brucei/Trypanosoma congolense) or single (T. brucei) infection. Of the 140 flies fed on animals with a mixed infection and examined 30 days later, 4 had a metacylic T. brucei infection, 29 a T. congolense infection and 13 a mixed T. brucei/T. congolense infection. There was no significant difference between the transmission rate of T. brucei as a single or as part of a mixed infection. The high proportion of mixed T.b. brucei/T. congolense infections was explained best by a model implying that if a fly is refractory to T. congolense, it is also refractory to T.b. brucei and vice versa. Hence, results suggest that the transmission of T.b. brucei is affected mainly by the vectorial capacity of flies and not by concurrent trypanosome infections in the host.     

Efficacy of doramectin 0.5% w/v Pour-On for control of the horn fly, Haematobia irritans

In 1998, three groups of cattle at three locations in Lousiana were treated with Dectomax^® (0.5% doramectin) Pour-On and horn fly populations were monitored. Acceptable levels (less than 50 flies per side) of horn fly control were observed from 4 to 8 weeks. Differences in the length of control among the three sites were most likely affected by immigration of adult flies from untreated groups. In 1999, acceptable horn fly control was obtained for 13 weeks by the use of two treatments of doramectin Pour-On.     

The control of Parafilaria bovicola transmission in South Africa

Ivermectin treatment of all cattle on a badly infected farm failed to interrupt the transmission of P. bovicola, even though ovipositional blood spots were drastically reduced in numbers for an entire summer season following treatment. Regular weekly to fortnightly dipping of all cattle in 50 ppm deltamethrin immediately reduced vector fly numbers to less than 1 fly per cow face. Sustained dipping for 9 months effectively reduced P. bovicola transmission from approximately 50% to less than 2%. However, cessation of fly control led to a return to predipping P. bovicola infection levels. Ovipositional blood spot counts and the ELISA technique for evaluating P. bovicola infection in a herd were compared and were both effective methods. Best results for the blood spot method, however, are obtained in spring at the peak of the bleeding season whereas the ELISA method does not have this limitation.     

The epidemiology of Parafilaria bovicola in the Transvaal Bushveld of South Africa

A total of 20 375 flies collected off cattle on 12 farms over 36 months were identified and examined for 3rd stage P. bovicola. The 3 vector species accounted for 64.1% of the flies collected and were the only fly species found to be infected. Musca lusoria was clearly the dominant vector fly, although large numbers of Musca sp. A appeared regularly between February and April each year. This phenomenon, coupled with high numbers of M. lusoria throughout most of the year, led to an increase in the numbers of vector flies from their lowest level in June to a peak in February-April. Of the 13 070 vector flies examined for 3rd stage larvae only 64 (0.52%) were positive; of these 41 were M. lusoria and 17 Musca sp. A. No positive male flies were found. Incubation of wild-caught flies for up to 13 days at 27 degrees C noticeably increased the larval recovery rate. Flies were found to be infected mainly from August-March. Infected M. lusoria were recorded from July-March and infected Musca sp. A from January-May. Only 6 infected M. xanthomelas were collected and this was during the period August-December, when most ovipositional blood spots occur on cattle. It is concluded that P. bovicola transmission in the Bushveld is not correlated with peak periods of bleeding but rather with high numbers of vector flies, the various species augmenting each other so that transmission may take place almost throughout the year.     

Role of horse flies in transmission of wquine infectious anemia from carrier ponies

Equine infectious anemia virus was transmitted from an acutely ill and an inapparently infected pony to uninfected ponies by the interrupted feeding of horse flies (tabanids). Transmission from acutely ill ponies was not accomplished following: (1) the interrupted feeding of a single horse fly, (2) bites of horse flies that had fed on an acutely affected pony 24 hours earlier, (3) bites of horse flies that had oviposited after feeding on an acutely affected pony, or (4) the inoculation of larval material derived from horse flies that had fed to repletion. It was concluded that horse fly transmission of equine infectious anemia virus is mechanical only and that infected horses that are free of clinical signs can be a source of virus for insect transmission.     

Exploratory trial to determine the efficacy of the PYthon and the PYthon Magnum slow-release insecticide ear tags for the control of midges (Culicoides spp.), attacking sheep and cattle and flies attacking cattle

This study investigated the prophylactic action of the chemical combination zeta-cypermethrin and piperonyl butoxide, administered by means of slow-release insecticide-impregnated ear tags, against biting midges (Culicoides spp) attacking sheep and against midges, horn flies (Haematobia irritant), stable flies (Stomoxys calcitrans), and houseflies (Musca domestica) attacking cattle. Treated sheep and cattle were protected 100 percent against blood-feeding midges for two months and there was a clear reduction in the number of midges collected from treated animals. Three days after the ear tags were attached to cattle, the number of horn flies on the cattle was reduced to practically zero and remained at a low level until the end of the trial (day 85). There was also a strong reduction in the numbers of stable flies and houseflies counted.     

Estimating the probability of effective transmission of trypanosomes using the poisson distribution

The trypanosome infection rate in cattle is determined by the probability of effective transmission (PET) of trypanosome from Glossina spp. to susceptible cattle. The PET in turn is a function of the rate of contact between cattle and Glossina spp. and was calculated using a Poisson probability distribution. Seven parameters determined the final form of the PET. These were: probability of at least one contact with Glossina spp. (PTC), probability that Glossina spp. will feed on the host (PFF), proportion of Glossina spp. which are non-tenerals (PNT), proportion of infected Glossina spp. (PTI), proportion of infected Glossina spp. which are infectious (PMTI), proportion of successful transmissions of the infective agent in inoculum of infectious Glossina spp. (PII), and finally, the probability for the presence of a susceptible host animal (PC). The product of these proportions provided an estimate of effective transmission of trypanosomes from infectious Glossina to susceptible cattle. The probability of this event varied between (0.0007 and 0.0009) or 7–9 infections per 10 000 susceptible cattle per year at a steady state.