Ebola knows no borders—and frontline aid teams (and even one of their pets) remain in the direct line of contagion.

This reality has become increasingly evident in recent days after one case of Ebola developed in Texas, triggering a massive U.S. public health response, and yesterday a nurse’s assistant in Spain was confirmed as the first person in the current outbreak to have contracted Ebola outside of Africa. In Sierra Leone, meanwhile, a European staffer of one aid organization was reported yesterday as having contracted the disease.

The infection of health care and aid workers is not unexpected for an infectious illness that has already claimed 3,400 lives, among them 200 health workers. The midcourse of the epidemic, however, is not showing signs of infecting other countries in west Africa beyond the three where it has reached epidemic levels. Meanwhile, the U.S. and other governments are taking precautionary steps but avoiding major restrictions on travel and commerce—and global health authorities are trying to tamp down any urge to panic.

The Spanish patient is in stable condition, with no symptoms besides a fever. The announcement by Madrid is only the latest in a string of cases where healthcare workers contracted Ebola in the course of caring for patients, often to the astonishment of the workers themselves who wonder how they may have contracted the illness because, in some cases, they do not recall any close contact without adequate personal protective equipment.

Doctors Without Borders, a key aid organization leading the Ebola response in west Africa, reported yesterday that a Norwegian staffer in Sierra Leone contracted the virus and is being sent to Europe for treatment. So far, other than a freelance NBC camera operator receiving care in Nebraska after being transferred there for care, the Dallas patient remains the only Ebola patient in the U.S.

Ebola is not an airborne infection and the World Health Organization has taken pains to point out that “spread of the virus via coughing or sneezing is rare, if it happens at all.” The virus is transmitted via direct physical contact with infected bodily fluids, the most infectious being blood, feces and vomit. It has a 21-day incubation period although patients usually begin displaying symptoms earlier, around 10 days after exposure to the virus. There is no indication that the pathogen is mutating to become more harmful. Its genetic makeup has remained stable—changing by only a half of a percent—since the beginning of the outbreak, CDC Director Tom Friedman said today in a press conference.

The new Spanish patient was working as a nurse’s assistant at the Carlos III Hospital in Madrid, helping to treat a patient who had been infected in Sierra Leone and medically evacuated by Spain to its captial on September 22, only to die three days later, according to WHO. Outside of two laboratory accidents in Russia where individuals accidentally pricked themselves with Ebola-laden needles, this represents the first case of someone contracting Ebola outside Africa.

Reportedly, the Spanish patient’s pet dog will be euthanized as part of the effort to control spread of the infection, although evidence of Ebola transmission via dogs is not clear. “There is one article in the medical literature that discusses the presence of antibodies to Ebola in dogs. Whether that was an accurate test or relevant we don’t know but clearly we want to look at all possibilities,” Friedman said. “We have not identified this as a means of transmission.”

In Texas the Ebola patient is now stable but in critical condition and being treated with brincidofovir, an oral medicine developed by Durham, N.C.–based biopharmaceutical company, Chimerix. The patient is on a ventilator to support his breathing and is receiving kidney dialysis. His liver function, which declined over the weekend, has improved, the Dallas hospital said, but doctors there caution that his condition could vary during coming days. So far, none of the 10 people who came into close contact with the patient nor 38 others who may have had lesser exposure have developed any symptoms of the virus.

After a week of political agitation by Louisiana Gov. Bobby Jindal and others for new flight restrictions on travel out of Ebola-stricken countries in west Africa, Pres. Barack Obama on Monday announced that the U.S. government will be ramping up its screening for the virus at domestic airports and in west Africa, but details of those changes have yet to be disclosed. “We’re working very intensively on the screening process both in places of origin and on arrival to the U.S. and we’re looking at that entire process,” CDC’s Friedman said today, adding that the administration would make further announcements in coming days. Right now, patients in affected west African countries are screened with thermometers for fever and fill out questionnaires prior to boarding a flight.

In west Africa, there are some indiciations that the virus is being contained, at least in specific areas. Fewer Ebola cases have appeared in some communities that previously had high case loads in Liberia’s capital, Monrovia, which Friedman said could potentially be attributed to the increase in Ebola isolation units and better burial practice protocols—yet it is too early to say whether the tide has turned. “Globally this is going to be a long, hard fight,” Friedman said. “The enemy here is a virus.”