Half a dozen students at Mountain View High School have contracted whooping cough since last month.Clark County Public Health has received reports of six cases of whooping cough, or pertussis, at the east Vancouver school since November. In response, school officials sent a letter home with students, alerting parents to the cases and the signs and symptoms of the disease.“Pertussis is just circulating in the community,” said Monica Czapla, infectious disease program manager at Clark County Public Health. “Because of the long incubation period and the long contagious period, it can be circulating for a while.”Whooping cough is an illness spread through respiratory secretions from coughing and sneezing. For the first few weeks, people with whooping cough can be contagious but only have seemingly harmless symptoms similar to those of a cold, such as runny nose, low-grade fever and mild cough.As the disease progresses, people with whooping cough may experience coughing fits, followed by a “whooping” noise, vomiting and difficulty catching their breath. The coughing fits can continue for 10 weeks or more, according to the Centers for Disease Control and Prevention.For infants, the illness is particularly dangerous — and potentially deadly. Babies who get whooping cough typically catch it from their older siblings or parents, according to health officials.