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Zhang Y, Zhang K, Wang M, Wu X, Liu J, Chu H, Zhang D, Li K, Huang H. Studies on the embryonic development and larval infection potential of the stomach bot flies, Gasterophilus pecorum. Int J Parasitol Parasites Wildl 2024; 23:100917. [PMID: 38419737 PMCID: PMC10901080 DOI: 10.1016/j.ijppaw.2024.100917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 02/15/2024] [Accepted: 02/16/2024] [Indexed: 03/02/2024]
Abstract
Endangered Przewalski's horses have faced severe infections from Gasterophilus pecorum (Diptera, Gastrophilidae) in Xinjiang's Kalamaili Nature Reserve (KNR). This study examines G. pecorum's development and infection patterns in embryonic and larval stages, crucial for understanding horse botfly disease in desert grasslands. For the incubation of G. pecorum fertilized eggs, we established the six distinct temperature gradients: 16 °C, 20 °C, 24 °C, 28 °C, 30 °C, and 32 °C. Using the least squares method, we calculated the correlation between the developmental threshold temperature of the eggs and their cumulative effective temperature. Furthermore, we meticulously recorded the survival duration of the larvae across a spectrum of temperature gradients (-20 °C, -10 °C, 4 °C, 10 °C, 20 °C, and 30 °C) and under varying conditions (dark and light). This method allows us to analyze and interpret the impact of these environmental factors on larval survival durations. 1) The formula for predicting the embryonic development period of G. pecorum was N = (182.7 ± 12.03)/[T-(3.191 ± 1.48)], where the developmental threshold temperature was 3.191 ± 1.48 °C, and the effective accumulated temperature was 182.7 ± 12.03 d°C 2) The model describing the relationship between the embryonic development rate and temperature was: y = 0.0001x2+0.0007x+0.0378, demonstrating a positive correlation between the development rate and temperature (R-sq = 0.989, p < 0.001). 3) Larvae in the dark group exhibited a longer survival time, with the longest being 9 months at 4 °C. The adaptation of G. pecorum's embryonic development to cold temperature, combined with the extended survival period of larvae in the egg state, significantly increases the infection potential of G. pecorum in colder climates. This discovery offers essential insights into the predominance of G. pecorum in the KNR region and provides a crucial biological basis for the prevention of myiasis and the conservation of vulnerable species, such as Przewalski's horses.
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Affiliation(s)
- Yu Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing, China
| | - Ke Zhang
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Science, Xining, China
| | - Meng Wang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing, China
| | - Xiaojia Wu
- Department of Biology Lund University, Lund, Sweden
| | - Jiawei Liu
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing, China
| | - Hongjun Chu
- Institute of Forest Ecology, Xinjiang Academy of Forestry, Urumqi, China
| | - Dong Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing, China
| | - Kai Li
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing, China
| | - Heqing Huang
- Chongqing Academy of Environmental Science, Chongqing, China
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Zhang K, Ju Z, Zhang Y, Wang C, Mubalake S, Hu D, Zhang D, Li K, Chu H. Developmental dynamics and survival characteristics of the common horse bot flies (Diptera, Gasterophilidae, Gasterophilus) in desert steppe. Vet Parasitol 2023; 315:109870. [PMID: 36701942 DOI: 10.1016/j.vetpar.2023.109870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Revised: 01/01/2023] [Accepted: 01/04/2023] [Indexed: 01/07/2023]
Abstract
The genus Gasterophilus (Diptera, Gastrophilidae) is an obligate parasite of the equine family that causes widespread myiasis in desert steppe. Based on four common naturally excreted Gasterophilus larvae collected systematically in the Karamaili Ungulate Nature Reserve from March to September 2021, this paper studies the population dynamics and ontogenetic laws of horse flies, and discuss the coexistence pattern and population dynamics prediction of horse flies. The results showed that the Gasterophilus larvae had obvious concentrated development period, and the time of population peaks was different, the earliest was G. nigricornis (late March), followed by G. pecorum-Ⅰ (mid-April), G. nasalis (late April), G. intestinalis (early May), G. pecorum-Ⅱ (mid-August). The order of development threshold temperature "Cnigricornis < Cpecorum-Ⅰ ≤ Cpecorum-Ⅱ < Cnasalis < Cintestinalis" is consistent with the peak order of different larval populations. The life history survival rate (L) was as follows: Lnigricornis (83.97%) ≥ Lintestinalis (81.25%) > Lnasalis (72.42%) ≥ Lpecorum-Ⅱ (71.65%) > Lpecorum-Ⅰ (39.23%). This study combined indoor experiments and field surveys revealed the development of horse fly populations with different life strategies in desert grasslands. Based on the different development threshold temperatures of several horse flies, the staggered population dynamics of Gasterophilus form continuous infection stress on the host. In addition, G. pecorum exhibited a univoltine bimodal population distribution in this area and led to two high-intensity host infections, which is one of the important reasons why it has become the dominant species of myiasis in desert steppe.
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Affiliation(s)
- Ke Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing 100083, China; Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Science, Xining 810008, Qinghai, China
| | - Zhongrui Ju
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing 100083, China
| | - Yu Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing 100083, China
| | - Chen Wang
- Mt. Kalamaili Ungulate Nature Reserve, Changji 831100, Xinjiang, China
| | - Shalitanati Mubalake
- Xinjiang Research Centre for Breeding Przewalski's Horse, Urumqi 831700, Xinjiang, China
| | - Dini Hu
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing 100083, China
| | - Dong Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing 100083, China
| | - Kai Li
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing 100083, China.
| | - Hongjun Chu
- Institute of Forest Ecology, Xinjiang Academy of Forestry, Urumqi 830063, China.
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Zhang K, Zhou R, Huang H, Ma W, Qi Y, Li B, Zhang D, Li K, Chu H. Host feces, olfactory beacon guiding aggregation of intestinal parasites Gasterophilus pecorum (Diptera: Gasterophilidae). Parasitol Res 2022; 121:2601-2613. [PMID: 35788769 DOI: 10.1007/s00436-022-07577-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Accepted: 06/14/2022] [Indexed: 11/30/2022]
Abstract
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.
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Affiliation(s)
- Ke Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Science, Xining, 810001, China
| | - Ran Zhou
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China
| | - Heqing Huang
- Chongqing Academy of Environmental Science, Chongqing, 401147, China
| | - Wei Ma
- Mt. Kalamaili Ungulate Nature Reserve, Changji, Xinjiang, 831100, China
| | - Yingjie Qi
- Mt. Kalamaili Ungulate Nature Reserve, Changji, Xinjiang, 831100, China
| | - Boling Li
- China National Environment Monitoring Center, Beijing, 100012, China
| | - Dong Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China
| | - Kai Li
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China.
| | - Hongjun Chu
- Institute of Forest Ecology, Xinjiang Academy of Forestry, Urumqi, 830063, China.
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Zhang K, Huang H, Zhou R, Zhang B, Wang C, Ente M, Li B, Zhang D, Li K. The impact of temperature on the life cycle of Gasterophilus pecorum in northwest China. Parasit Vectors 2021; 14:129. [PMID: 33648570 PMCID: PMC7923332 DOI: 10.1186/s13071-021-04623-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2020] [Accepted: 02/03/2021] [Indexed: 11/22/2022] Open
Abstract
Background The departure of the mature larvae of the horse stomach bot fly from the host indicates the beginning of a new infection period. Gasterophilus pecorum is the dominant bot fly species in the desert steppe of the Kalamaili Nature Reserve (KNR) of northwest China as a result of its particular biological characteristics. The population dynamics of G. pecorum were studied to elucidate the population development of this species in the arid desert steppe. Methods Larvae in the freshly excreted feces of tracked Przewalski’s horses (Equus przewalskii) were collected and recorded. The larval pupation experiments were carried out under natural conditions. Results There was a positive correlation between the survival rate and the number of larvae expelled (r = 0.630, p < 0.01); the correlation indicated that the species had characteristic peaks of occurrence. The main periods during which mature larvae were expelled in the feces were from early April to early May (peak I) and from mid-August to early September (peak II); the larval population curve showed a sudden increase and gradual decrease at both peaks. Under the higher temperatures of peak II, the adults developing from the larvae had a higher survival rate, higher pupation rate, higher emergence rate and shorter eclosion period than those developing from peak I larvae. Although G. pecorum has only one generation per year, its occurrence peaked twice annually, i.e. the studied population has a bimodal distribution, which doubles parasitic pressure on the local host. This phenomenon is very rarely recorded in studies on insect life history, and especially in those on parasite epidemiology. Conclusion The period during which G. pecorum larvae are naturally expelled from the host exceeds 7 months in KNR, which indicates that there is potentially a long period during which hosts can become infected with this parasite. The phenomenon of two annual peaks of larvae expelled in feces is important as it provides one explanation for the high rate of equine myiasis in KNR. ![]()
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Affiliation(s)
- Ke Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China
| | - Heqing Huang
- Chongqing Academy of Environmental Science, Chongqing, 401147, China
| | - Ran Zhou
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China
| | - Boru Zhang
- Qinhuangdao Forestry Bureau, Qinhuangdao, 066004, Hebei, China
| | - Chen Wang
- Mt. Kalamaili Ungulate Nature Reserve, Changji, 381100, Xinjiang, China
| | - Make Ente
- Xinjiang Research Centre for Breeding Przewalski's Horse, Urumqi, 831700, Xinjiang, China
| | - Boling Li
- China National Environment Monitoring Centre, Beijing, 100012, China
| | - Dong Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China
| | - Kai Li
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, 100083, China.
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Huang H, Zhang B, Chu H, Zhang D, Li K. Gasterophilus (Diptera, Gasterophilidae) infestation of equids in the Kalamaili Nature Reserve, China. ACTA ACUST UNITED AC 2016; 23:36. [PMID: 27593434 PMCID: PMC5018932 DOI: 10.1051/parasite/2016036] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2016] [Accepted: 08/16/2016] [Indexed: 11/14/2022]
Abstract
We investigated infections with Gasterophilus spp. in three equids within the Kalamaili Nature Reserve (northern China). We conducted necropsies on 6 Przewalski's horses (Equus ferus przewalskii) and 6 Mongolian wild asses (Equus hemionus) and administered ivermectin to 10 overwintering domestic horses to expel parasites during winter periods. All 22 equids studied (100%) were infested with Gasterophilus spp. and a total of 17,225 larvae were collected. These included six species: G. haemorrhoidalis, G. inermis, G. intestinalis, G. nasalis, G. nigricornis, and G. pecorum. The mean intensity of Gasterophilus spp. larvae was 1904 in Przewalski's horses, 780 in Mongolian wild asses, and 113 in domestic horses. Gasterophilus pecorum was the most abundant species in all three equids. Przewalski's horses, a reintroduced species, had a significantly higher intensity of Gasterophilus spp. than the Mongolian wild ass, indicating greater susceptibility to parasites in its ancestral home.
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Affiliation(s)
- Heqing Huang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing 100083, PR China
| | - Boru Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing 100083, PR China
| | - Hongjun Chu
- Wildlife Conservation Office of Altay Prefecture, Altay 836599 Xinjiang, PR China
| | - Dong Zhang
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing 100083, PR China
| | - Kai Li
- Key Laboratory of Non-Invasive Research Technology for Endangered Species, College of Nature Conservation, Beijing Forestry University, Beijing 100083, PR China
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The incidence and species composition of Gasterophilus (Diptera, Gasterophilidae) causing equine myiasis in northern Xinjiang, China. Vet Parasitol 2016; 217:36-8. [DOI: 10.1016/j.vetpar.2015.12.028] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2015] [Revised: 12/26/2015] [Accepted: 12/28/2015] [Indexed: 11/18/2022]
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Ibrayev B, Lider L, Bauer C. Gasterophilus spp. infections in horses from northern and central Kazakhstan. Vet Parasitol 2014; 207:94-8. [PMID: 25522954 DOI: 10.1016/j.vetpar.2014.11.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Revised: 11/13/2014] [Accepted: 11/14/2014] [Indexed: 11/26/2022]
Abstract
A cross-sectional survey was performed to obtain current data on the gastrointestinal myiasis of horses in the provinces of Kostanay, Akmola and Karagandy, northern and central Kazakhstan. The stomach, small intestine and rectum of 148 slaughter horses were examined for Gasterophilus spp. larvae during a 26-month study period. All horses were infected with 2nd and 3rd stage larvae (mean intensity: 803±350), and 22% of them harboured >1000 Gasterophilus spp. larvae each. Four species were identified: G. intestinalis (prevalence: 100%; mean intensity: 361±240 larvae), G. haemorrhoidalis (100%; 353±191), G. nasalis (100%; 73±36) and G. pecorum (91.2%; 18±10). Horses aged<2 years were higher infected with Gasterophilus larvae than 2-4 years old animals. Both the prevalence and extremely high intensity of Gasterophilus infections of horses in these Kazakh regions suggest respective control measurements to improve the health and performance of the animals and to increase the economic income of horse owners.
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Affiliation(s)
- Baltabek Ibrayev
- S Seifullin Kazakh Agro Technical University, Faculty of Veterinary Medicine, 62 Prospect Pobedy, 010011 Astana, Kazakhstan
| | - Lyudmila Lider
- S Seifullin Kazakh Agro Technical University, Faculty of Veterinary Medicine, 62 Prospect Pobedy, 010011 Astana, Kazakhstan
| | - Christian Bauer
- S Seifullin Kazakh Agro Technical University, Faculty of Veterinary Medicine, 62 Prospect Pobedy, 010011 Astana, Kazakhstan; Institute of Parasitology, Justus Liebig University Giessen, Schubertstrasse 81, 35392 Giessen, Germany.
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Gasterophilosis: a major cause of rectal prolapse in working donkeys in Ethiopia. Trop Anim Health Prod 2011; 44:757-62. [DOI: 10.1007/s11250-011-9961-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/14/2011] [Indexed: 10/17/2022]
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Otranto D, Stevens JR, Brianti E, Dorchies P. Human and livestock migrations: a history of bot fly biodiversity in the Mediterranean region. Trends Parasitol 2006; 22:209-13. [PMID: 16563866 DOI: 10.1016/j.pt.2006.03.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2005] [Revised: 02/20/2006] [Accepted: 03/08/2006] [Indexed: 10/24/2022]
Abstract
The bot fly (oestrid) is responsible for myiasis in domestic animals. The presence in some regions of southern Europe of an unusually large number of different species of bot fly suggests a high degree of oestrid biodiversity in this area. The many factors that can influence parasitic species composition (e.g. host and parasite genetics, relationships with their hosts and environment, and animal management) include the movement of domestic animals in association with migrating human populations in southern Europe over thousands of years. From its geographical position, which was strategically important in controlling commercial trade routes in early Western civilization, the Mediterranean sea has for more than 3000 years constituted the hub of many different cultures, populations, genes and agricultural practices. The movement of animals and their associated parasites in this region can help to explain the evolution of parasitic biodiversity.
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Affiliation(s)
- Domenico Otranto
- Department of Animal Health and Welfare of the Faculty of Veterinary Medicine, University of Bari, PO Box 7, 70010 Valenzano (Bari), Italy.
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Otranto D, Milillo P, Capelli G, Colwell DD. Species composition of Gasterophilus spp. (Diptera, Oestridae) causing equine gastric myiasis in southern Italy: parasite biodiversity and risks for extinction. Vet Parasitol 2005; 133:111-8. [PMID: 15978726 DOI: 10.1016/j.vetpar.2005.05.015] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2004] [Revised: 04/21/2005] [Accepted: 05/13/2005] [Indexed: 11/26/2022]
Abstract
Horse gastrointestinal myiasis caused by larvae of Gasterophilus spp. (Diptera, Oestridae) flies has a worldwide distribution and, where present, it is primarily caused by larvae of Gasterophilus intestinalis and Gasterophilus nasalis. Other species, i.e., Gasterophilus inermis, Gasterophilus pecorum and Gasterophilus haemorrhoidalis, present in different or in the same regions of the gastrointestinal tract, were only occasionally reported in very limited areas of eastern European Countries and in central Italy. With the aim to contribute data on the species composition of Gasterophilus and on the seasonal variation of the infection pattern in southern Italy, 152 native horses were necropsied from January to December 2003 and Gasterophilus larvae were collected from the stomach, the small intestine and the rectum of each of them. On the whole, 125 (82.2%) horses were infected by larvae of Gasterophilus spp. and 214 second stage larvae (L2) and 13,342 third stage larvae (L3) collected. Five species of Gasterophilus were identified with the following prevalence: G. intestinalis=95.2%, G. nasalis=44.8%, G. inermis=15.2%, G. pecorum=2.6% and G. haemorrhoidalis=0.8%. L3 were retrieved throughout the observation period with the highest mean burdens from January to August 2003 while the lowest mean was registered from September to November 2003. L2 were collected in February-March 2003 and from September to December 2003. The majority of the animals (n=66, 43.4%) were infected with a single Gasterophilus species, however, 45 animals (29.6%) harboured 2 species, 12 animals (7.9%) 3 species and 2 animals (1.3%) 4 species. The trend of abundance in the L3 of G. intestinalis and G. nasalis, the most represented species, was highly concordant (r=0.5, p<0.001). A retrospective comparison of our results and of other data from four seasons of observation (1983-1986) in central Italy showed that the number of G. inermis, G. pecorum and G. haemorrhoidalis have been decreasing relative to G. intestinalis and G. nasalis which may suggest tendency toward the extinction of the three former species of Gasterophilus.
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Affiliation(s)
- Domenico Otranto
- Department of Animal Health and Welfare, Faculty of Veterinary Medicine, University of Bari, Valenzano, Bari, Italy.
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