Vaccine-preventable diseases: Poliomyelitis, measles, and an international wake-up call

The devastated health care infrastructure in Syria has hindered immunization programs, leaving millions of citizens vulnerable to vaccine-preventable diseases [14]. Vaccination coverage in Syria is estimated to have dropped from 91% in 2010 to as low as 45% in some regions by 2013, indicating rapid collapse of immunization systems in conditions of war [3]. Of the 1.8 million Syrian children born since the conflict, over 50% are unvaccinated [15]. Consequently, 36 cases of poliomyelitis have been officially reported in Syria after 15 years of eradication [16]. Although the opposition-held northeastern province of Deir Ez Zur has been the epicenter of the outbreak, cases have been encountered in rural areas of Damascus, Aleppo, and other regions [17].

The poliomyelitis virus lives in sewage, water, and contaminated food. In Syria, raw sewage is pumped directly into the Euphrates River, which provides drinking and washing water to villages and chlorination to decontaminate the water has been discontinued since 2012 [15]. The strain of poliomyelitis in Syria has been linked to the wild-type poliovirus 1 (WPV1) from Pakistan, which is suspected to have been introduced to Syria by Pakistani jihadist fighters [18], [19]. The same strain was detected in the sewage of Cairo in December 2012 and in sewage in Israel and the West Bank shortly thereafter, without any clinical cases thanks to high vaccination rates in these areas [20]. WPV1 can easily and undetectably spread, with only one in two hundred unvaccinated infected individuals developing acute flaccid paralysis [18]. WHO estimates that over 7,600 Syrians are currently infected, since poliomyelitis thrives in unsanitary, crowded conditions and among malnourished children [21].

In response to this outbreak, the biggest immunization campaign in the region's history led to the vaccination of over 2.7 million Syrian children and 23 million in neighboring countries [13]. The campaign employed the bivalent oral polio vaccine, which challenges a child's immune response with the two remaining types of virus and can be used in short intervals for acute outbreak responses [20], [22]. Nevertheless, the constantly migrating population, the lack of precise monitoring mechanisms, and besieged locations that remain out of reach to immunization threaten the success of this campaign. While cases are yet to be reported in Lebanon and Jordan, Iraq has confirmed the first case of poliomyelitis, after a 14-year hiatus, in northern Baghdad [23].

This poliomyelitis outbreak has helped focus international attention on the severity of the ongoing health crisis in Syria, as well as the importance of reinvigorating eradication campaigns in the endemic countries of Afghanistan, Pakistan, and Nigeria to prevent the recurrence of such outbreaks [17]. Polio in Syria has been declared a public health emergency that requires international efforts and solidarity to prevent a global epidemic.

The hampering of immunization efforts has also contributed to the spread of other vaccine-preventable diseases such as measles. Overcrowding, unsanitary conditions, and the efficient transmissibility of measles make the Syrian population highly susceptible to acquiring and spreading the infection. Measles has swept through Syria, including Aleppo and the northern regions, with over 7,000 confirmed cases [24]. This epidemic has not spared refugees in neighboring countries, even among highly vaccinated populations [14]. In Jordan, 24 cases of measles were reported in 2012, while over 200 cases were reported in 2013 [25]. In Lebanon, nine reported cases of measles in 2012 increased to 1,760 cases in 2013, only 13.2% of which were among Syrian refugees [26]. The growing rate of infection among Lebanese nationals reveals how conditions of unrest have exploited deficiencies in Lebanon's measles immunization coverage to contribute to a regional crisis. In response, the Lebanese Ministry of Public Health launched a national immunization campaign in April 2014 with over 4,200 trained volunteers administering vaccines for polio, measles, and rubella [27].

While ongoing vaccination campaigns have tried to address this epidemic, challenges continue to prevent adequate coverage. Unlike the poliomyelitis vaccine, which is relatively easy to transport and is administered orally, the measles vaccine must remain chilled and is administered by injection, posing a challenge for aid workers trying to reach vulnerable populations. Although immunization campaigns continue to deliver vaccines for measles and poliomyelitis to millions of adults and children in Syria and the surrounding region, the ongoing civil war restricts access to entire districts, threatens the lives of volunteers in the immunization campaign, and hinders efforts to quell the ongoing humanitarian crisis.

Leishmaniasis and a region at risk

The risk factors for cutaneous leishmaniasis, including malnutrition, poor housing, population displacement, and poverty, are unfortunately all met in the case of the Syrian crisis, transforming the national epidemic of cutaneous leishmaniasis into a regional threat [28]. Cutaneous leishmaniasis has been endemic in parts of Syria, mainly Aleppo, for decades [29]. However, the Syrian conflict and vast population displacement has significantly increased the incidence of the vector-borne disease within Syria and spread this epidemic into neighboring countries. Reported cases of cutaneous leishmaniasis in Syria continue to rise, with the last official figure reporting 52,982 confirmed cases in 2012 [30].

Lebanon had no cases of cutaneous leishmaniasis before 2008 and sporadic cases in the following years. By 2013, 1,033 cases were confirmed, 96.6% (998) of which were among Syrian refugees [26]. In recently published data on 1,275 patients from 213 displaced Syrian families in Lebanon, the average age among infected individuals was 17 years, with many patients presenting with multiple disfiguring lesions (Figure 1). 77% of the patients manifested the disease after being in Lebanon for more than eight weeks, which is the known incubation period for cutaneous leishmaniasis, suggesting that the sand fly vector was transported to Lebanon with the incoming refugees [31]. Speciation by PCR showed that 85% of cases were caused by Leishmania tropica, with 15% of cases as Leishmania major [31].

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Figure 1. Syrian child from a Lebanon refugee camp, presenting multiple lesions from cutaneous leishmaniasis, courtesy of Dr. Ibrahim Khalifeh

https://doi.org/10.1371/journal.ppat.1004438.g001

The dense concentration of refugees, the similar environmental conditions, and the limited health care access in rural areas contribute to the higher burden of leishmaniasis in Lebanon. This epidemic has raised concerns that the sand fly vector may find a permanent habitat in Lebanon, particularly in rural areas with a high density of Syrian refugees such as the Bekaa valley, which holds 70% of all reported cases [32]. This outbreak has been the first of its kind in more than a decade and will continue to grow within the upcoming summer months if left unaddressed [32]. The Lebanese Ministry of Public Health (MOPH) and relevant governmental departments are planning a coordinated campaign to contain the spread of the infection, which includes spraying pesticides to kill the vector, providing free treatment and diagnosis for emerging cases and monitoring disease activity [32]. In April 2013, the Lebanese MOPH, in conjunction with WHO, organized workshops to train doctors across Lebanon to recognize the condition. In addition to the growing threat of leishmaniasis, experts have warned against the emergence of other vector-borne diseases such as dengue fever and malaria [33].