Relja Beck
Hrvatski veterinarski institut, Zagreb, Hrvatska
E-mail: relja.beck@gmail.com
Hrvatski veterinarski institut
Razvojem molekularnih metoda te njihova redovita primjena u istraživanjima i redovnoj dijagnostici značajno je doprinijela otkrivanju novih uzročnika i/ili novih izolata što je potaknulo detaljnija istraživanja vektorskog potencijala ponajprije komaraca, krpelja, komarčića (Culicoides) ali i ostalih člankonožaca. Procjenjuje se da gotovo 39 000 različitih vrsta artropoda može parazitirati na ljudima te domaćim i divljim životinjama što jasno ukazuje na njihov globalni značaj. Republiku Hrvatsku odlikuju velike razlike u reljefu, tlu i klimi pojedinih regija čemu su se prilagodile i brojne vrste člankonožaca.
Poznato je da su u Europi najzačajniji vektori krpelji, uspješni vektori uzročnika bolesti u ljudi i životinja. Danas je poznato 907 vrsta s različitim vektorskim potencijalom.
Najznačajnija vrsta Ixodes ricinus uspješno prenosi zoonotske uzročnike poput bakterije Borrelia burgdorferi sensu lato, virus krpeljnog encefalitisa, rikecije Anaplasma phagocytophilum, Rickettsia monacensis, kandidata vrste Neoehrlichia mikurensis te protozoe poput vrste Babesia microti i B. venatorum (EU 1). Morfološka determinacija vektora je zahtjevna i često subjektivna. Stoga se danas provode brojna istraživanja sa ciljem razvoja novih objektivnijih metoda za njihovo razlikovanje kao i istraživanja njihova vektorskog kapaciteta. Dokaz uzročnika u vektoru ili njegove DNA ne znači da ga može uspješno prenijeti stoga su neophodna pokusna istraživanja i objektivan dokaz mogućnosti prijenosa. Vrste komarčića unutar Pulicaris kompleksa nije moguće morfološki razlikovati, a samo pojedine vrste mogu prenijeti virus bolesti plavog jezika stoga je nužna primjena genskih metoda za razlikovanje vrsta. Na ovaj način je u RH dokazano najmanje 6 novih vrsta komarčića kao i nove genske varijante poznatih vrsta čija uloga u širenju i održavanju virusa je u potpunosti nepoznata. Komarac Aedes albopictus (azijski tigrasti komarac) predstavlja invazivnu vrstu, ali i uspješnog prijenosnika parazitarnih i virusnih bolesti. Ovaj komarac posjeduje podjednak afinitet za ubadanje životinja i ljudi čime omogućava uspješniji prijenos zoonotskih uzročnika poput oblića Dirofilaria repens.
Vektori za emergentne bolesti često i nisu poznati ili nisu istraživani stoga je teško procijeniti širenje, ali i prežiljavanje uzročnika u potencijalnim vektorima. Na primjeru bolesti kvrgave kože jasno je vidljivo da nepozavanje vektora otežava kontrolu i suzbijanje bolesti. Osnovni način prijenosa je mehanički, a postoji sve više dokaza da se virus može prenijeti i putem različitih stadija krpelja, odnosno da može perzistirati u populaciji krpelja. U krpelja Rhipicephalus appendiculatus i R. decoloratus dokazan je transstadijski i transovarijski prijenos, što znači da virus mogu prenijeti na novu generaciju ličinke krpelja (transovarijski), a zatim i na druge razvojne stadije krpelja (nimfe, adulte). Pokusno je dokazano da ličinke hranjene na viremičnim govedima, nakon presvlačenja u nimfe, mogu prenijeti virus na neificirana goveda koja su kasnije razvila klasičan oblik bolesti. Navedene vrste nisu prisutne u Europi no može se pretpostaviti da druge vrste krpelja iz roda Rhipicephalus mogu imati vektorski kapacitet. Sadašnjim istraživanjima roda Rhipicephalus otkrili smo postojanje potencijalno „nove“ vrste za koju se do sada smatralo da je R. sanguineus temeljem morfoloških analiza. Nalaz je značajan jer dovodi u pitanje prijenos novih uzročnika kao što su Anaplasma centrale, A. ovis i A. bovis.
Culicoides punctatus pripada skupini Culicoides pulicaris kompleks te predstavlja dominantnu skupinu komarčića u RH, a C. punctatus je jedna od najčešćih vrsta.
U 2015. godini bile su prisutne već u travnju u kontinentalnoj Hrvatskoj. DNA virusa bolesti kvrgave kože dokazana je u Turskoj tijekom epidemije iz 2015. godine u vrsti C. punctatus. Na primjeru emergentne bolesti kvrgave kože, jasno je vidljivo da nedostaju temeljne spoznaje o vektorima tog do sada nepoznatog uzročnika u Europi.
Vectors of emerging infectious diseases and their distribution in Croatia
Relja Beck, Croatian Veterinary Institue, Zagreb, Croatia, E-mail: relja.beck@gmail.com
D iseases transmitted by vectors are attracting increasing attention in recent years due to global changes that directly affect the ecology of pathogens and their spread.
Climate change promotes the spread of the vector in new areas, and at the same time globalization enables faster transmission of vectors and their animal hosts. The development of molecular methods and their use in research and routine diagnostics significantly contributed to discovery of new pathogens and/or new isolates which encouraged more detailed studies of the vector potential especially mosquitoes, ticks, biting midges (Culicoides) or other arthropods. It is estimated that almost 39,000 different species of arthropods parasite humans, domestic and wild animals, which clearly points their global importance. Croatia has large variations in relief, soil and climate of certain regions which allowed adaptation of numerous species of arthropods. In Europe the most important vectors are ticks, able to transmit successfully pathogens to humans and animals. Today it is known 907 species of ticks with different vector potential. The most significant species Ixodes ricinus transmit zoonotic pathogens such as bacteria Borrelia burgdorferi, the tick-borne encephalitis virus, rickettsial patthogens Anaplasma phagocytophilum, Rickettsia monacensis, candidate species Candidatus Neoehrlichia mikurensis and protozoa such as Babesia microti and B. venatorum (EU 1), thus has a significant potential for transmission of zoonotic pathogens. Morphological determination of vector species is demanding and often subjective, therefore, today researchers are focused to develop new more objective methods for their determination and to explore their vector capacity. Detection of pathogen’s DNA in the vectors does not mean that it can be transmit to new host therefore experimental studies are needed to evaluate vector capacity of each proposed vector. Culicoides within Pulicaris complex cannot be distinguished morphologically, but only certain species can transmit bluetongue virus, therefore is necessary to apply genetic methods to distinguish species. Using that approach in Croatia at least 6 new species and a new genetic variants of known species have been confirmed, whose role in the dissemination and maintenance of the virus is completely unknown. Mosquito Aedes albopictus (Asian tiger mosquito) is an invasive species but also an excellent vector of parasitic and viral diseases.
This mosquito has equal affinity for bitting animals and humans, which enables successful transmission of zoonotic pathogens such as nematode Dirofilaria repens.
Vectors for emerging diseases are often not known or have not been investigated thus is difficult to assess their spread and surviving. For example, in case of viral lumpy skin disease it is clear that without knowledge on vectors is difficult to control disease spreading. Main mode of transmission is mechanical, but there are evidences that the virus can be transmitted through different stages of ticks and can persist in the population of ticks. In Rhipicephalus appendiculatus and R. decoloratus trans-stadial and trans-ovarial transmission have been proven, indicating the virus can be transmitted to the new generation of larval ticks (trans-ovarian), and then to other developmental stages of ticks (nymphs, adults). Experimental studies has shown that the larvae fed on viremic cattle, after molting into nymphs can transmit the virus to non-infected cattle which later developed the classic form of the disease. These species are not present in Europe, but it is to assume that other ticks of the genus Rhipicephalus possess vector capacity. In the current research of the genus Rhipicephalus we discovered the existence of a potential “new” type which is so far considered to be R. sanguineus based on morphological analysis. The finding is significant prejudice to the transfer of new pathogens such as Anaplasma centrale, A. ovis and A. bovis.
Culicoides punctatus belongs to a Culicoides pulicaris complex and the dominant group of biting midges in Croatia, and C. punctatus is one of the most common species. In 2015, it was detected in April in continental Croatia and at the same time was the most common type in Slavonia. DNA of lumpy skin disease virus has been confirmed in C. punctatus during the 2015 outbreak in Turkey. On the example of emerging lumpy skin disease, it is clear that there is lack of basic knowledge of vectors for, so far unknown pathogen in Europe.