I gatti sono considerati il serbatoio primitivo del Toxoplasma gondii perchè nel loro intestino avviene il ciclo riproduttivo sessuale, o primario, del Toxoplasma. I gatti si infettano cibandosi delle carni di roditori, uccelli e piccoli animali. Negli ultimi anni si è ridimensionata l’attenzione nei confronti del gatto come portatore della malattia, in particolare se si tratta di un gatto domestico, alimentato con prodotti in scatola e la cui lettiera è cambiata tutti i giorni (le cisti del parassita si schiudono dopo tre giorni a temperatura ambiente e alta umidità). Il vero serbatoio primario della
toxoplasmosi è invece rappresentato dai gatti randagi, che si infettano cacciando uccelli e topi contaminati, e che possono defecare nel terreno rilasciando oocisti di Toxoplasma che contaminano acqua, erba, foraggio, verdure e frutta che vengono ingeriti da suini, bovini, ovini e uccelli. Questi ultimi rappresentano gli ospiti intermedi del toxoplasma. Anche l’uomo rientrare fra gli ospiti intermedi potendosi contaminare direttamente con l’ingestione di frutta e verdure contaminate o a contatto con gatti o altri animali contaminati. Ma più frequentemente la contaminazione dell’uomo avviene con l’ingestione di carne cruda o poco cotta contenente oocisti di toxoplasma (30-70%).
- test diagnostici diretti: coltura cellulare, amplificazione del genoma (PCR, Polymerase Chain Reaction);
- test diagnostici indiretti: IFA (immunofluorescenza indiretta), ELISA (IgA, IgM, IgG), ISAGA (immunoassorbimento per IgM), Western-blot, test di avidità per le IgG.
TERAPIA: Il trattamento di elezione nella toxoplasmosi congenita rimane l’associazione pirimetamina (Daraprim® cpr 25 mg) e sulfadiazina (Sulfadiazina® cpr 500 mg), prese individualmente o già confezionate in associazione (Metakelfin® cpr 25 mg + 500 mg). La terapia dovrebbe essere intrapresa con lo scopo di prevenire la notevole incidenza di sequele tardive segnalate nei bambini che ricevono trattamento inadeguato o nessun trattamento. Entrambi i farmaci sono efficaci sulla forma attiva del ciclo vitale del parassita (tachizoita); il razionale della terapia durante l’infezione acuta è appunto quello di distruggere i tachizoiti e prevenirne la trasformazione in nuove cisti, su cui questi farmaci non sono attivi. La pirimetamina e la sulfadiazina esercitano un effetto sinergico contro il T. gondii interferendo sul suo metabolismo dei folati in due punti diversi. L’attività combinata dei due farmaci è di otto volte superiore a quella ottenibile con la somma dei singoli effetti. Grazie a questa azione sinergica sulla via di sintesi dei folati, è possibile ridurre il dosaggio della pirimetamina e quindi moderarne gli effetti ematotossici. La sulfadiazina si somministra al dosaggio di 100 mg/kg/die in 2 somministrazioni giornaliere per 12 mesi di terapia. La tollerabilità di entrambi i farmaci è buona e non sono segnalati effetti di tossicità, né discrasie ematologiche o patologie maligne a insorgenza tardiva, nei neonati che siano stati trattati a lungo con pirimetamina e sulfadiazina. Posologia compresse (combinazione 25 mg di pirimetamina e 500 mg di sulfadiazina), per os, in monosomministrazione:
- <1 anno di età: 0,25 cp/die
- 1-3 anni: ½ cp/die
- 4-8 anni: 1 cp/die in
- 9-14 anni: 2 cp/die
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