The relative importance of different transmission routes of Toxoplasma gondii has been a matter for debate. This ubiquitous parasite is generally thought to be transmitted by infective oocysts excreted by the definitive host, the cat. Ingestion of undercooked meat has also been considered an important route of transmission in many mammals while congenital transmission has generally been considered relatively rare. Experimental studies demonstrate the ability of T. gondii to be transmitted congenitally, but few studies have investigated the frequency of this transmission route in natural populations. We use PCR amplification of the SAG1 gene to investigate the frequency of congenital transmission in a wild population of mice (Mus domesticus) and show that congenital transmission is occurring in 75% of pregnancies in this population. Furthermore, for infected pregnant mice, transmission occurs to at least one foetus in 100% of cases while variable penetrance of congenital infection is observed. These high levels of congenital transmission in this wild population of mice, taken together with other recent data on congenital transmission in sheep, suggests that this phenomenon might be more widespread than previously thought.

This parasite has been previously reported in the nasal passages of foxes in the UK (Lapage 1968), but the recent cases have been seen in imported stray dogs from Romania, where dogs are routinely fed on raw meat. There are reports, in Romanian journals, of a prevalence of infection with L serrata nymphs of 20 to 40 per cent in the mesenteric lymph nodes of slaughtered domestic ruminants (M. Ionita, Faculty of Veterinary Medicine of Bucharest, personal communication). The parasite is also potentially zoonotic with rare human infections reported (Acha and Szyfres 2003). These infections have included parasite localisation in the eye requiring surgical intervention (Koehsler and others 2011, Pal and others 2011). Therefore, where the parasite is confirmed or suspected, strict hygiene measures during pet handling should be observed by the owner and all those who have contact with the animal, as eggs could be expelled via the oral, nasal or faecal routes, or contaminate the animal's coat. Nasal flushing with warm salty water may help to detach the parasites in the dog. Screening of suspected infected animals by identification of eggs in nasal flushes could also be carried out. Surgical removal of the parasite may not be curative as they can attach to the sinuses. Macrocyclic lactones are used as a treatment in Romania. There is a report of parasite expulsion following milbemycin oxime treatment in a dog (Gjerde 2013) and also that injectable ivermectin was effective against a related species, Linguatula arctica, in reindeer (Haugerud and others 1993). There has been an incident of the related species, L arctica, being detected in the nasal cavity and distal bronchi of a three-year-old reindeer in Great Britain that died of an unrelated condition. This parasite is reported as being relatively common in semi-domesticated reindeer in northern Norway (Gjerde 2013).