**2.1. Overview**

Protozoa and helminthes can affect the lung as a primary site, or a complication. Some para‐ sites have a migration cycle through the lung (larva migrans), inducing blood and tissue eo‐ sinophilia. Tissue and peripheral blood eosinophilia are elicited by chimiotactic activity of released inflammatory mediators, such as cytokines (IL-3, IL-5), which play a key role in ac‐ tivation and differentiation of eosinophils. Eosinophils secrete various substances, some with antiparasitis properties, others favoring tissue damage in targeted organs. Elevated IgE level observed in these conditions relay on the Th2-lymphocytes, stimulating antibodies production by B-lymphocytes (Om P Sharma, 1991; VijayanVK, 2008).

Clinical manifestations of the lung involvement could be acute: asthma –like syndrome, or Loeffler's syndrome, with dyspnea, wheezing, cough (Ford RM, 1996); or chronic such as he‐ moptysis or right heart failure signs. Acute manifestations depend on immunological reac‐ tion (hypersensitivity), and chronic feature relay on the mechanical action of pathogen on the vessels and tissues. (vg: schistosoma eggs in the pulmonary artery and pulmonary hy‐ pertension). (Santiago M et *al*., 2005).

Löeffler's syndrome represent transient clinical, immunological and radiological manifesta‐ tions due to parasites whose life cycle elicit a transit through the lung or not, and to drug reactions

Hypereosinophilia observed in this syndrome is antigen –induced, and circulating IL-5, is the key mechanism for the recruitment and differentiation of the eosinophils.

#### **2.2. Helminthic parasites**

The three classes of helminths (Cestoidea, Trematoda, and Nematoda) can affect the lung.

#### *2.2.1. Nematodes and the lung*

This group include: ascariasis, strongyloidiasis,ancylostomiasis, tropical pulmonary eosino‐ philia, pulmonary dirofilariasis, and pulmonary trichinellosis.

#### 2.2.1.1. Pulmonary ascariasis

Ascariasis is a round worm infection caused by Ascaris lumbricoides. This nematode dis‐ ease affects ± 25% of the world population whose 95% are in Africa (Crompton, 1999).
