EPIDEMIOLOGICAL STUDIES ON HELMINTHOSES IN GOATS AND SHEEP CAUSED BY PROTOSTRONGYLIDAE LEIPER , 1926

Studies on sheep, goats and terrestrial snails from a pasture in a north-eastern Bulgarian region have been carried out. Protostrongylids of 4 genera – Muellerius, Cystocaulus, Protostrongylus and Neostrongylus have been established. The infection extensity in goats is higher than that in sheep while the generic diversity is greater in sheep. In tracing the season dynamics in the parasitic infections of the end hosts it has been established that during the summer the infection extensity is permanently kept in its high values. In the autumn a drop in infection extensity is observed but the amount of the larvae released with faeces is augmented reaching its maximum in November-December. A relative increase in the infection extensity as well as in the larval output is observed in February and solely for the larval output such an increase is recorded in April. Season dynamics in the spread of the different protostrongylid genera in the end hosts and the influence of age and sex on larval output have been traced. The season dynamics of the extensity and intensity of the infection of the snails on the pasture has also been followed up. H. obvia is the intermediate host of greatest importance for the spread of protostrongylidoses in the region under study.


Materials and methods / Materijal i metode rada
Digital data were processed after the statistical methods of Sepetliev (1980).

Investigations on the end hosts:
The results from the monthly investigation of the faecal samples from arbitrarily chosen sheep and goats of the flock are given in Table 1.The infection extensity (IE) with protostrongylids of the goats is 88.09 percent.It is higher than the one established so far in Bulgaria (79.8 percent -Zurliiski and Russev, Š40¹; 71.2 percent -Halacheva et al.Š1¹) but is lower than the one reported for Morocco -100 percent Š3, 5¹ and Spain -98 % Š1¹.There are three genera established in the goats -Muellerius, Cystocaulus and Neostrongylus with IE being for these genera as follows: 88.09 percent, 34.92 percent and 0.79 percent respectively.In the sheep IE is 62.35 percent which is twice higher than the one reported for the sheep in Turkey -33.8 percent Š28¹.There are four genera established for the sheep: Muellerius -50 percent IE; Protostrongylus -14.12 percent IE; Neostrongylus -11.76 percent IE and Cystocaulus -11.28 percent IE.In the sheep and the goats 39 percent of the infections are mixed.Multigeneric protostrongylid infections have been also established in a previous study of ours in wild ruminants in Bulgaria Š29¹.
The dynamics of the infection in the end hosts during the different months of the survey is shown in Figure 1.In the sheep IE is relatively constant during the summer period -from 66.7 percent to 77.8 percent.During the greater remaining part of the year a monthly alternation of peaks and declines is observed, the maximum being recorded in February -100 percent.In the goats IE is high almost throughout the whole year, over 80 percent, the second half of the year being kept at 100 percent except for the months of July and October.During the first half of the year an alternation of peaks and declines in IE is also observed though not so marked as in the case of the sheep.The average IE for both species of end hosts displays peaks in February, April and December, while in the summer months it is permanently maintained as high.
The season dynamics in the spread of the different protostrongylid genera has been traced and graphically presented in Figure 2 and Figure 3. From Figure 2 it is clear that IE of the Cystocaulus genus in the goats displays monthly peaks and declines in the first half of the year and has greater values as compared to the second half.In the summer, after June, the IE with Cystocaulus starts to drop gradually and toward the end of autumn and in the winter it is gradually increased without reaching values over 36.4 percent.The rate of infection with the Muellerius genus is high throughout the whole year.Except for the weakly pressed   (Strazhitsa, Bulgaria, 2004-2005) Slika 3. Dinamika rasprostranjenosti rodova Protostrongylidae po godi{njim dobima kod ovaca (Stra`ica, Bugarska, 2004-2005)  drops in February and May, IE is steadily kept over 80 percent during the year being 100 percent for the better part of the months.It is quite clear from Figure 3 that the protostrongylid generic diversity in the sheep is different during the different months of the year.It is noteworthy that the Muellerius genus is every month present in the lung fauna, throughout all seasons the IE with this particular genus being rather higher than that with the rest of the protostrongylid genera.During the spring and summer the generic diversity is at its maximum, all four genera of helminths established in the sheep being present.During the autumn and winter (from September till February) Muellerius has mainly been registered.
For that period the genera Neostrongylus and Protostrongylus were recoreded only twice at a time and the Cystocaulus genus just once.The Muellerius genus is the most widespread one both among the goats and the sheep.This is most probably due to the high resistance, great longevity and the prolonged preservation of infection capacities of L1 in the environment Š31, 27, 14, 36¹.This makes it possible for a great number of animals to be infected for a longer period.For the Neostrongylus genus larvae the survival capacity according to Reguera-Feo et al.Š31¹ and Morrondo-Pelayo et al.Š27¹ is quite low.
The amount of protostrongylid larvae in 1 gramme of faeces (LPG) has been calculated every month for every one of the marked goats (Table 2).The mean monthly values of this parameter in the adult goats and cubs are compared and the results are shown in Figure 4.The graph clearly states that there are several peaks in the larval output in the adults.The first one is observed in February 2004 -a total of 1537 larvae and the next one is in April -2537.During the other months up till September, the larval output vacillates without surpassing 2000 LPG.During the months of autumn and winter, October, November and December, the larval output is abruptly increased reaching its maximum in December -6414 LPG.In the next two months it falls under 2000 and at the end of the winter it rises again over that level -2316.The increased larval output in February 2004 and February -March 2005 is accounted for by the so-called baby-delivery leap of the infection due to the lowered resistance of the organism as a result from the stress.Other authors have also observed this phenomenon in animals during the last months of gestation or around birth Š10, 32, 4¹.
The increase of the larval output in April may be due to several reasons: spring enhancement of the sexual production of the adult helminths, activation of the histotropic larvae latent during the winter and now reaching sexual maturation, and the attenuated immunity of the host caused by the lack of antigenic stimuli during the winter.The protostrongylid larval output augmentation during the autumn and winter is probably due to an increased sexual production of the helminths with which the animals have been infected during the spring and summer.This could also be brought about by the lowered resistance of the animals due to the impaired conditions of living -low temperatures, lack of green food, etc.These results are in accordance with those of Diez-Banos et al.Š32¹ according to whom IE with protostrongylids in sheep decreases during the warm  Protostrongylid larval output (PLO) in young goats has been established for the first time 5 to 6 months after their birth.This is the period of the encounter of the young animals with infectious larvae on the pasture, the overcoming of maternal immunity and development of the helminths to sexual maturity.The larval output in this age group is significantly augmented during the autumn and winter months but the peak is in November -1 month prior to that for the adult goats and the LPG amount is significantly greater -12960 which can be assigned to the fact that the cubs have been infected for the first time in the calendar year during which their immune system has also been under construction.After November the larval output in young goats decreases.
The influence of sex on PLO has been traced by interpreting the results from the investigations on the animals before 1 year of age (Figure 5).PLO is higher in the male cubs during all months of the study save for February that could be attributed to baby-delivery in the females.
A number of authors in Bulgaria have reported a protostrongylid IE growth with age Š12, 2, 30, 40, 25¹, others, however, have reported just the opposite or have established differences due to the protostrongylid species Š16, 7¹.Up till the present moment, however, the influence of the host's age on the amount of protostrongylid larvae released with the faeces has not been studied in our country.It is obvious from the present study (Fig. 6) that PLO also rises with age which is in accord with other authors reporting on this fact Š9, 32¹.

Investigations on the intermediate hosts:
The following snail species have been gathered during the entire field study on the pasture: Helicella obvia ŠMenke, 1828¹, Monacha cartusiana ŠMueller, 1774¹ and Bradybaena fruticum ŠMueller, 1774¹.H. obvia is the most common species with density in some places in the pasture of over 300 snails per square metre and a presence during the entire period from May to October.H. obvia is followed by M. cartusiana -with much lower density and found during three of the studied months.A total of 5 juvenile specimens of the B. fruticum species were found in September and October.The results from the snail studies are presented in Table 3.The degrees of parasitic infection of both major species on the pastures are compared in Table 4. IE is higher in H. obvia than that in M. cartusiana, which is in accordance with the data of Georgiev Š17¹ about the Stara Zagora region.As for the infection intensity (II) the opposite trend is valid which contradicts the above- quoted author.In one experimental studies we have also recorded a higher II in M. cartusiana as compared to the one found in H. obvia (unpublished data).Season dynamics of the infection intensity and extensity with protostrongylid larvae of the snails is presented in Figure 7.It is evident from it that IE is at its highest during the summer -between 30 percent and 35 percent, and it is comparatively high in spring -24 percent and lowest in the autumn -8.6 percent.Similar dynamics is also observed for II but in this case a peak month (August) is registered in the summer after which it shows a smooth decline.
According to authors from Europe, Joyeux and Gaud, 1946;Davtian, 1950;Zdarska, 1960, quoted by Sumnaliev Š33¹ the extensity of protostrongylid infection in the gastropods displays two peaks -a spring and an autumn one.The studies of Sumnaliev Š33¹ about the Sofia area confirm this tendency in relation to the species Neostrongylus lineatus and Cystocaulus ocreatus.In other species he observed one peak for each -in the summer for M. capillaris and in the autumn for the Protostrongylus sp.For the Shumen region the author observed the highest IE with protostrongylids in H. obvia at the end of spring -the beginning of summer, but not in all years of the studies.According to Zurliiski Š39¹ the extensity of protostrongylid infections in the gastropods in the Varna area displays a peak in the autumn and according to Georgiev and Georgiev Š18¹ this parameter for the Stara Zagora region is higher in the summer rather than in the autumn.The months June and July are found as peak ones for the protostrongylid infection of mollusks in Poland Š26¹ while Manga-Gonzalez and Morrondo-Pelayo Š24¹ have noted the months July, August, September and October as peak ones for Spain.In Tunisia, Lahmar et al.Š22¹ have established that the infection in the snails is high from February till April (at the end of the humid period) and later with the increase of the temperature and subsiding of the showers the infection in the snails decreases in size.From the above-presented we can draw the conclusion that the season dy-  (Strazhitsa, Bulgaria, 2004) Slika 7. Dinamika Protostrongylidae infekcija po godi{njim dobima kod pu`eva (Stra`ica, Bugarska, 2004) Ekstenzivnost infekcije % Intenzivnost infekcije namics in the infection of gastropods with protostrongylids depends on the climatic and geographical characteristics of the region under study, as well as on the concrete conditions during the research period.
In conclusion the epidemiology of the protostrongylidoses in the climate-geographical conditions of north-eastern Bulgarian can be summed up in the following manner.In spring being activated the intermediate hosts start progressively to contract infection.The peaks in IE and PLO in the end hosts are also favorable factors.II in the gastropods is gradually on the rise in the summer, reaching its peaks in August after which it starts to drop, while IE is permanently preserved around its highest values from June to September.The availability of a constant source of infection for the end hosts during these months quite logically explains the lasting maintenance of IE in them as well.In the autumn, together with the decrease of IE and II in the snails, a diminution of IE in the end hosts is observed while larval output starts to increase reaching its maximum in November-December.The augmentation of the IE and PLO values in the end hosts is also observed in February due to the conditions of the birth delivery period.
The higher IE in the goats and the greater generic diversity in the sheep render these two species of end host topical, each one in a specific way, for the epidemiology of protostrongylidoses.
Due to the high IE and the great density of the intermediate hosts H. obvia we consider the species to be of greatest importance for the spread of these helminthoses in the studied region.

Figure 3 .
Figure 3. Season dynamics of prevalence of protostrongylid genera in sheep(Strazhitsa, Bulgaria, 2004-2005) Slika 3. Dinamika rasprostranjenosti rodova Protostrongylidae po godi{njim dobima kod ovaca(Stra`ica, Bugarska, 2004-2005) number of larvae (under 100) have been established after the method of Vaida / mali broj larvi (manji od 100) ustanovljeno je po metodi Vaida NI -not investigated / nije ispitano N -sample, negative for protostrongylids / uzorak negativan na Protostrongylidae months and is on the rise during the cold ones.They are also consistent with the findings of Richard et al.Š32¹ who have established higher IE values and augmented quantitative larval excretion for Muellerius capillaris in lactating goats during the autumn as opposed to spring.

FigureFigure 5 .FigureFigure 4 .
Figure 5. Influence of sex on protostrongylid larval output in young goats