The number of countries and territories confirming local Zika virus circulation continues to grow, with Trinidad and Tobago becoming the 29th such location in the Americas, while the Marshall Islands also reported its first locally acquired case.

In other developments, the World Health Organization (WHO) recently released a risk assessment for Africa, noting that its initial assessment shows some nations are at more risk than others.

Newest affected areas

Trinidad and Tobago's health ministry on Feb 17 announced the first lab-confirmed Zika virus infection in a 61-year-old woman who had recently traveled to New Zealand, but it said the case was probably locally acquired and that further investigation was under way.

Over the past few days the Pan American Health Organization (PAHO) added it to the list of nations or territories experiencing local spread.

In a related development, the WHO today shared more details about the first local cases reported in other recently affected Caribbean locations, the Dutch territories Aruba and Bonaire, both located in the southern Caribbean just north of Venezuela's coast. The WHO said Bonaire's case was confirmed on Feb 12 and that the Netherlands reported the first four cases from Aruba on Feb 16, three in residents and one in a tourist. In addition, island has also reported seven travel-linked cases in people who were infected in Brazil, Colombia, and Venezuela.

Elsewhere, the Marshall Islands recently reported its first locally acquired case, the European Centre for Disease Prevention and Control (ECDC) said Feb 20 in its weekly communicable disease report. The ECDC said that, according to the Pacific Public Health Surveillance Network, the first local Marshall Islands case was reported in a pregnant woman at 12 weeks gestation on Feb 14.

Risk assessment for Africa

The WHO said though no systematic surveillance has been in place for tracking Zika virus in Africa, sporadic cases have been reported on the continent for many years. The agency added that the virus may be endemic in many parts of the continent where Aedes aegypti, the main vector of the disease, is prevalent.

Though it's possible that some portion of the African population may have some immunity, the strain spreading rapidly in the Americas may not be known to African populations and could lead to a more acute disease, the WHO warned. "Vigilance must also be maintained."

In the current outbreak, Cape Verde is the only African nation to report cases, more than 7,000 of them from October through December 2015. However, the WHO said that, based on available data, the number of cases has been declining since December.

All countries in the African region are at risk for Zika virus transmission, because A aegypti mosquitoes are widely distributed and transmit several arboviruses on the continent. The WHO said the mosquito has adapted to and flourishes in urban settings found in many African cities, where poor water storage and drainage conditions can increase breeding sites for the mosquitoes.

African countries vary in their access to healthcare and disease detection and management, and ones with strong health systems are likely to cope better with a Zika outbreak, according to the WHO. The agency looked at the vulnerability of 47 countries in the region based on composite measures of hazards, vulnerabilities, and lack of coping capacity.

The WHO said all of the countries are at some risk, but it added that nearly half (20) of the countries were categorized as high risk, with Comoros, Guinea-Bissau, Central African Republic, Madagascar, and South Sudan in the top five. The five countries with the lowest risk were South Africa, Namibia, Swaziland, Mauritius, and Ghana.

The agency urged countries to take actions based on its risk assessment. For example, it said high-risk countries should be prioritized for health system support and vector control investments, and lower-risk countries should receive communication and general advisory support.

Other developments

Dutch clinicians, in a Feb 19 letter to The Lancet, described subcutaneous bleeding and thrombocytopenia in a 54-year-old woman with a confirmed Zika virus infection who returned to Amsterdam after visiting family in January in Suriname, where local circulation is under way. Her infection was confirmed in Suriname on the second day of her illness.

Ten days later she developed hematomas on her arms and legs, along with gastrointestinal symptoms, which were still apparent—along with some fresh ones—when she returned to the Netherlands and was seen at a travel medicine clinic on day 17 of her Zika infection. Lab studies were notable for slight microcytic anemia and profound thrombocytopenia—a deficiency of blood platelets.

On day 29 of her illness she developed gum bleeding, and her doctors treated her for presumed immune-mediated thrombocytopenia with intravenous immunoglobulins. They noted that mild thrombocytopenia has been described only once in the past with Zika infection and that unpublished reports suggest that moderate thrombocytopenia is relatively rare.

Brazil's health ministry also notified the WHO of a fatal Zika virus case, based on an atypical presentation of the disease, according to a Feb 17 epidemiologic update from PAHO. The information came from a retrospective investigation into the case by the Evandro Chagas Institute.

The 20-year-old woman from Rio Grande do Norte state got sick on Apr 11, 2015, and was admitted to an intensive care unit when her condition worsened, which included heavy bleeding, and she died. Blood samples on Apr 17 were negative for dengue virus, but samples from her liver, kidney, and lungs were positive for Zika virus. Autopsy revealed diffuse pulmonary infiltrate and bilateral pulmonary abscesses. The investigation into the woman's death is ongoing.

PAHO also noted four Zika-linked deaths from Suriname in a 2-week period. It said all were in men ages 61 to 75 years old who had underlying medical conditions. PAHO said all had a short period of diarrhea and vomiting, followed soon after by a worsening of their conditions and death.

Experts interviewed by the New York Times raised concerns that Zika virus could be among the infectious agents that trigger mental illnesses later in life such as autism, bipolar disorder, and schizophrenia.

The experts pointed out that the diseases arise from a combination of factors, but infections in utero, including viral ones, are thought to be a trigger. W Ian Lipkin, MD, director of the Center for Infection and Immunity at Columbia University's Mailman School of Public Health, told the Times, "The consequences of this go way beyond microcephaly."

Experts in fetal development told the paper that viral infections in early pregnancy can affect brain growth and lead to microcephaly, but infections later in pregnancy can cause less obvious but still significant damage.