In 2001, the WHO established a set of guidelines to assist onchocerciasis programs to determine whether interruption of transmission had occurred and MDA with ivermectin could be stopped [16
]. The process outlined by WHO involves four phases: (1) suppression of transmission, where new infective stage larvae are no longer introduced into the human population by the vectors, but the parasite population maintains the ability to recover if interventions are withdrawn; (2) interruption of transmission, when the parasite population is thought to be unable to recover and interventions (in this case, twice-yearly ivermectin treatment) can be halted; (3) precertification, during which time posttreatment surveillance is needed for three years with an in depth evaluation to take place during the second or third year, depending on the peak transmission season [20
]; (4) if this evaluation was negative, a declaration of elimination. When all foci within a country reach the final phase, the country may request certification of elimination of onchocerciasis from WHO [16
We conducted an assessment of the status of O. volvulus
transmission in the third onchocerciasis focus of Guatemala to be so evaluated by this process. Data from evaluations conducted by the MOPH in Huehuetenango in the 1990s indicated that the parasite had, at best, a tenuous hold when MDA was launched in 1996. Our results in 2007-2008 confirmed that transmission of onchocerciasis had been successfully interrupted in Huehuetenango after 22 rounds of MDA over 13 years. We found no evidence of ocular lesions attributed to O. volvulus
infection. Similarly, we found no serological evidence of recent exposure to the parasite among 6–12-year-old children residing in the endemic area, nor any entomological evidence of infected or infective black fly vectors. The maximum STP in this area was conservatively calculated at 1.2 infective larvae/person/season, which is not sufficient to sustain transmission in S. ochraceum
]. The expert steering committee of OEPA (the Program Coordinating Committee (PCC)) reviewed the results of this evaluation and formally recommended to the Guatemala MOPH that MDA with ivermectin be suspended in Huehuetenango, beginning in 2009. This recommendation was accepted, and Huehuetenango joined the Santa Rosa and Escuintla-Guatemala foci in the posttreatment surveillance period.
One challenge to maintaining the Huehuetenango focus free of onchocerciasis is its proximity to the border with Mexico () and, in particular, to the South Chiapas onchocerciasis focus [19
]. There has been conjecture that the two foci were linked through migrant coffee workers moving between the two countries and acquiring onchocerciasis in one or both foci. The unlikelihood of migrant workers being able to maintain onchocerciasis transmission in Guatemala and Mexico has been studied and discussed elsewhere [25
]. Of the two foci, South Chiapas historically had the highest levels of active onchocerciasis transmission in all of Mexico [19
] whereas the evidence from Huehuetenango during the same time period showed significant decreases in onchocerciasis prevalence even before the MDA program, suggesting that South Chiapas had little effect on transmission in Huehuetenango. An MDA program requiring treatment four times per year was required to interrupt transmission in the South Chiapas focus; at the beginning of 2012 MDA was suspended and post treatment surveillance initiated there [27
], thus it is unlikely that onchocerciasis could be reintroduced into Huehuetenango from Mexico.
Following PTS guidelines [20
], from December 2010 to April 2011 an entomological evaluation was conducted in Huehuetenango to verify that O. volvulus
transmission had not recrudesced. The results from this evaluation showed that O. volvulus
L3 are not circulating in the primary vector S. ochraceum
or in potentially a secondary vector, S. metallicum
. A conservative calculation of STP using upper 95% confidence interval values for S. ochraceum
was 1.1 infective larva/person/season, which is insufficient to maintain the parasite population. Thus we conclude that O. volvulus
transmission has been eliminated from the Huehuetenango focus. Currently in Guatemala the three hypoendemic foci (Santa Rosa, Escuintla-Guatemala and Huehuetenango) have demonstrated, through completion of PTS, elimination of transmission. The only focus that is currently under post treatment surveillance is the hyperendemic central endemic focus, which only stopped MDA at the beginning of 2012. When the Central Endemic focus successfully completes PTS and attains elimination status, then the entire country of Guatemala will be able to request WHO certification of elimination in 2015.
In May 2009, the US President Barack Obama announced a new Global Health Initiative (GHI) to improve health outcomes in partner countries. Neglected tropical diseases feature prominently in the GHI, and a key target is elimination of onchocerciasis from the Americas (http://www.america.gov/st/texttrans-english/2010/August/20100817134101su0.3731152.html
, accessed on September 1, 2010). As the elimination of onchocerciasis from the Americas by 2015 looks to be on target, this could be one of the early successes of the GHI and a significant public health success story that can help motivate and inform other elimination efforts.