(DAR ES SAALAM, Tanzania) — Health officials are investigating a deadly outbreak of a mystery disease in southern Tanzania that has infected over a dozen people and killed at least three of them.

Tanzania’s chief medical officer, Dr. Aifelo Sichalwe, urged the public to “remain calm” as he gave a briefing Wednesday from the capital, Dodoma. So far, a total of 13 cases of the unknown illness have been reported in Mbekenyera village in the East African nation’s Lindi region, with patients exhibiting symptoms similar to Ebola or Marburg virus diseases — fever, headache, fatigue and bleeding, especially from the nose, according to Sichalwe.

However, Sichalwe said preliminary results from laboratory testing has ruled out the Ebola and Marburg viruses in these cases, and that the patients had also tested negative for COVID-19.

The first case was recorded at Mbekenyera Health Center on July 5 and within three days, the hospital had received a second case, according to Sichalwe.

While three of the 13 patients have since succumbed to the strange disease, two who were isolated at Mbekenyera Health Center have recovered and returned home. Five patients remain in isolation, Sichalwe said.

The Tanzanian Ministry of Health has dispatched a team of experts to Lindi region to investigate the outbreak and take measures to prevent further spread of the unknown illness, such as conducting contact tracing, identifying people with similar symptoms and isolating them. Anyone who has had contact with confirmed or suspected cases are being monitored for 21 days, according to Sichalwe, who advised anyone experiencing similar symptoms to seek medical attention immediately.

The Tanzanian health ministry did not immediately respond to ABC News’ request for comment or additional information.

Dr. Fiona Braka, team lead for emergency responses at the World Health Organization’s regional office for Africa, confirmed that “WHO teams in Tanzania are working closely with” teams from the Tanzanian health ministry (MoH) “to investigate the disease further and are monitoring the situation closely.”

“The Tanzania MoH released a statement on Wednesday indicating that they have done an initial assessment and all investigations so far are negative for Ebola and Marburg,” Braka told ABC News in a statement Friday. “WHO and MoH teams are working on getting further testing done to rule out other diseases, including conducting sequencing of the samples. Currently, there is no new information on the cause of this illness.”

On Thursday, the WHO warned that Africa is facing a growing risk of outbreaks caused by zoonotic pathogens that originate in non-human animals and then switch species and infect humans. There has been a 63% increase in the number of zoonotic outbreaks in the region in the decade from 2012 to 2022, compared with 2001 to 2011, according to a new analysis by the United Nation’s global health arm.

The analysis found that between 2001 and 2022, there were 1,843 substantiated public health events recorded in the WHO African region, of which 30% were zoonotic disease outbreaks. While these numbers have increased over the last two decades, the WHO noted, there was a particular spike in 2019 and 2020 when zoonotic pathogens represented around 50% of public health events. Ebola virus disease and other viral hemorrhagic fevers constitute nearly 70% of these outbreaks, while dengue fever, anthrax, plague, monkeypox and a range of other diseases make up the remaining 30%, according to the analysis.

“Infections originating in animals and then jumping to humans have been happening for centuries, but the risk of mass infections and deaths had been relatively limited in Africa. Poor transport infrastructure acted as a natural barrier,” Dr. Matshidiso Moeti, the WHO’s regional director for Africa, said in a statement Thursday. “However, with improved transportation in Africa, there is an increased threat of zoonotic pathogens traveling to large urban centers. We must act now to contain zoonotic diseases before they can cause widespread infections and stop Africa from becoming a hotspot for emerging infectious diseases.”

The WHO warned that there can be a devastating number of cases and deaths when zoonotic disease arrive in cities, as several West African countries saw with the 2014-2016 Ebola outbreak — the largest and deadliest on record.

“We need all hands on deck to prevent and control zoonotic diseases such as Ebola, monkeypox and even other coronaviruses,” Moeti added. “Zoonotic diseases are caused by spillover events from animals to humans. Only when we break down the walls between disciplines can we tackle all aspects of the response.”

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