**3. Clinical signs in animals and humans**

#### **3.1. Toxoplasmosis in humans**

The clinical spectrum of the disease varies widely and depends primarily on the immune status of the host and *Toxoplasma* lineage to which a person was exposed. In humans, toxoplasmosis may manifest basically in five ways: asymptomatic, acute infection, congenital, ocular and the immunocompromised patient. In immunocompetent persons toxoplasmosis is usually asymptomatic or develops mild symptoms that go unnoticed in 80–90% of cases [27]. The usual clinical manifestations, trend to be laterocervical lymphadenopathy which is often treated, less frequently supraclavicular nodes, occipital, inguinal, mediastinal lymph node or any other chain are affected; patients with lymphadenopathy also have other symptoms such as fever, malaise, arthralgia, asthenia, night sweats, sore throat or maculopapular rash, no itching, which usually spares the palms and soles. The clinical picture of acute toxoplasmosis is usually benign and self-limiting; in <1 month, progression to the severe form is rare in immunocom‐ petent hosts [27–30]. In immunocompromised subjects, acute toxoplasmosis usually occurs widely where the main sites of spread are the central nervous system, eyes, heart, liver and lungs, with preference in the tissues where the immune response is limited, causing injuries. In immunocompromised patients, such as AIDS patients with very low CD4 counts, patients under immunosuppression to prevent or treat transplant rejection and fetuses, a reactivation of an earlier infection, rather than a newly acquired one, is common. In these individuals the parasite can induce besides encephalitis and retinochoroiditis, carditis, pneumonia, and meningitis, among other manifestations [31]. Ocular toxoplasmosis is produced in most cases by breaking tissue cysts that are congenitally acquired; however, it can occur in acquired infections too. It manifests as uveitis or retinochoroiditis with exudate and decreased vision; the lesion can be observed by fundus evaluation. The ocular presentation is commonly characterized by necrotic lesions destroying retinal architecture, sometimes engaging and choroid (retinochoroiditis) [28,30]. CT is the most significant complication of active infection. When the infection is acquired during pregnancy, either by reactivation of latent-phase bradyzoites or by a primary infection, the parasites migrate to the placenta and from there to the fetus. The severity of the disease depends on the stage of pregnancy when the parasites cross the placenta. At the beginning of pregnancy, fetal infection is rare, but when it happens, it triggers severe injury or death of the fetus. As the pregnancy progresses, congenital infection is most common, but the damage tends to be lower [29,32]. When the disease occurs in utero, there may be consequences observed at birth. Most congenital infections are asymptomatic, although in some cases the child is born with acute illness, where cases of hydrocephalus, eye damage and visceral can be found. In other cases, the disease develops after birth or become dormant for a long time [29,32].

#### **3.2. Toxoplasmosis in animals**

Natural infection in non-pregnant animals usually elapses without symptoms, but primary infection during pregnancy can cause embryonic death, abortion, birth weak or clinically normal but infected animals. Globally, *T. gondii* is the cause of 11–14% of the abortions that occur in sheep and goats [33]. In cattle, by contrast, *T. gondii* infection is not considered a common cause of abortion and presented asymptomatic. *T. gondii* in dogs is considered an opportunistic pathogen and infection is usually subclinical, but under certain conditions clinical signs are present, predominantly respiratory and neuromuscular manifestations (Dubey, 2010). Cats even as definitive hosts usually enrolled asymptomatic infection, even during removal of oocysts; however, sometimes clinical signs are present, primarily associated with respiratory type interstitial pneumonia, dyspnea, lethargy and anorexia, ocular signs (uveitis, retinochoroiditis) or neuromuscular signs [34]. In cats it has also been described as intrauterine infection; thus, infected animals generally have more severe signs: encephalitis, hepatitis, ascites, respiratory signs and perinatal death or weaning [35]. In the pigs, the disease usually attends in subclinical and can be seen in some cases of weak animals born or stillborn; in adult animals weight loss, anorexia and fever have been observed, which usually disappear by the third week after infection regardless of variant of *T. gondii*. Pigs are considered an important source of infection for humans because of the high parasite loads encountered in their tissues compared to other productive animals [22,35].
